LIBJXL: JPEG XL Encoder API

LIBJXL

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JPEG XL Encoder API
JPEG XL library (libjxl)
Collaboration diagram for JPEG XL Encoder API:

## Files
file | encode.h
| Encoding API for JPEG XL.
file | stats.h
| API to collect various statistics from JXL encoder.

## Classes
struct | JxlEncoderOutputProcessor
struct | JxlChunkedFrameInputSource

## Typedefs
typedef struct JxlEncoderStruct | JxlEncoder
typedef struct JxlEncoderFrameSettingsStruct | JxlEncoderFrameSettings
typedef void(* | JxlDebugImageCallback) (void *opaque, const char *label, size_t xsize, size_t ysize, const JxlColorEncoding *color, const uint16_t *pixels)
typedef struct JxlEncoderStatsStruct | JxlEncoderStats

## Enumerations
enum | JxlEncoderStatus { JXL_ENC_SUCCESS = 0 , JXL_ENC_ERROR = 1 , JXL_ENC_NEED_MORE_OUTPUT = 2 }
enum | JxlEncoderError { JXL_ENC_ERR_OK = 0 , JXL_ENC_ERR_GENERIC = 1 , JXL_ENC_ERR_OOM = 2 , JXL_ENC_ERR_JBRD = 3 , JXL_ENC_ERR_BAD_INPUT = 4 , JXL_ENC_ERR_NOT_SUPPORTED = 0x80 , JXL_ENC_ERR_API_USAGE = 0x81 }
enum | JxlEncoderFrameSettingId { JXL_ENC_FRAME_SETTING_EFFORT = 0 , JXL_ENC_FRAME_SETTING_DECODING_SPEED = 1 , JXL_ENC_FRAME_SETTING_RESAMPLING = 2 , JXL_ENC_FRAME_SETTING_EXTRA_CHANNEL_RESAMPLING = 3 , JXL_ENC_FRAME_SETTING_ALREADY_DOWNSAMPLED = 4 , JXL_ENC_FRAME_SETTING_PHOTON_NOISE = 5 , JXL_ENC_FRAME_SETTING_NOISE = 6 , JXL_ENC_FRAME_SETTING_DOTS = 7 , JXL_ENC_FRAME_SETTING_PATCHES = 8 , JXL_ENC_FRAME_SETTING_EPF = 9 , JXL_ENC_FRAME_SETTING_GABORISH = 10 , JXL_ENC_FRAME_SETTING_MODULAR = 11 , JXL_ENC_FRAME_SETTING_KEEP_INVISIBLE = 12 , JXL_ENC_FRAME_SETTING_GROUP_ORDER = 13 , JXL_ENC_FRAME_SETTING_GROUP_ORDER_CENTER_X = 14 , JXL_ENC_FRAME_SETTING_GROUP_ORDER_CENTER_Y = 15 , JXL_ENC_FRAME_SETTING_RESPONSIVE = 16 , JXL_ENC_FRAME_SETTING_PROGRESSIVE_AC = 17 , JXL_ENC_FRAME_SETTING_QPROGRESSIVE_AC = 18 , JXL_ENC_FRAME_SETTING_PROGRESSIVE_DC = 19 , JXL_ENC_FRAME_SETTING_CHANNEL_COLORS_GLOBAL_PERCENT = 20 , JXL_ENC_FRAME_SETTING_CHANNEL_COLORS_GROUP_PERCENT = 21 , JXL_ENC_FRAME_SETTING_PALETTE_COLORS = 22 , JXL_ENC_FRAME_SETTING_LOSSY_PALETTE = 23 , JXL_ENC_FRAME_SETTING_COLOR_TRANSFORM = 24 , JXL_ENC_FRAME_SETTING_MODULAR_COLOR_SPACE = 25 , JXL_ENC_FRAME_SETTING_MODULAR_GROUP_SIZE = 26 , JXL_ENC_FRAME_SETTING_MODULAR_PREDICTOR = 27 , JXL_ENC_FRAME_SETTING_MODULAR_MA_TREE_LEARNING_PERCENT = 28 , JXL_ENC_FRAME_SETTING_MODULAR_NB_PREV_CHANNELS = 29 , JXL_ENC_FRAME_SETTING_JPEG_RECON_CFL = 30 , JXL_ENC_FRAME_INDEX_BOX = 31 , JXL_ENC_FRAME_SETTING_BROTLI_EFFORT = 32 , JXL_ENC_FRAME_SETTING_JPEG_COMPRESS_BOXES = 33 , JXL_ENC_FRAME_SETTING_BUFFERING = 34 , JXL_ENC_FRAME_SETTING_JPEG_KEEP_EXIF = 35 , JXL_ENC_FRAME_SETTING_JPEG_KEEP_XMP = 36 , JXL_ENC_FRAME_SETTING_JPEG_KEEP_JUMBF = 37 , JXL_ENC_FRAME_SETTING_USE_FULL_IMAGE_HEURISTICS = 38 , JXL_ENC_FRAME_SETTING_FILL_ENUM = 65535 }
enum | JxlEncoderStatsKey { JXL_ENC_STAT_HEADER_BITS , JXL_ENC_STAT_TOC_BITS , JXL_ENC_STAT_DICTIONARY_BITS , JXL_ENC_STAT_SPLINES_BITS , JXL_ENC_STAT_NOISE_BITS , JXL_ENC_STAT_QUANT_BITS , JXL_ENC_STAT_MODULAR_TREE_BITS , JXL_ENC_STAT_MODULAR_GLOBAL_BITS , JXL_ENC_STAT_DC_BITS , JXL_ENC_STAT_MODULAR_DC_GROUP_BITS , JXL_ENC_STAT_CONTROL_FIELDS_BITS , JXL_ENC_STAT_COEF_ORDER_BITS , JXL_ENC_STAT_AC_HISTOGRAM_BITS , JXL_ENC_STAT_AC_BITS , JXL_ENC_STAT_MODULAR_AC_GROUP_BITS , JXL_ENC_STAT_NUM_SMALL_BLOCKS , JXL_ENC_STAT_NUM_DCT4X8_BLOCKS , JXL_ENC_STAT_NUM_AFV_BLOCKS , JXL_ENC_STAT_NUM_DCT8_BLOCKS , JXL_ENC_STAT_NUM_DCT8X32_BLOCKS , JXL_ENC_STAT_NUM_DCT16_BLOCKS , JXL_ENC_STAT_NUM_DCT16X32_BLOCKS , JXL_ENC_STAT_NUM_DCT32_BLOCKS , JXL_ENC_STAT_NUM_DCT32X64_BLOCKS , JXL_ENC_STAT_NUM_DCT64_BLOCKS , JXL_ENC_STAT_NUM_BUTTERAUGLI_ITERS , JXL_ENC_NUM_STATS }

## Functions
JXL_EXPORT uint32_t | JxlEncoderVersion (void)
JXL_EXPORT JxlEncoder * | JxlEncoderCreate (const JxlMemoryManager *memory_manager)
JXL_EXPORT void | JxlEncoderReset (JxlEncoder *enc)
JXL_EXPORT void | JxlEncoderDestroy (JxlEncoder *enc)
JXL_EXPORT void | JxlEncoderSetCms (JxlEncoder *enc, JxlCmsInterface cms)
JXL_EXPORT JxlEncoderStatus | JxlEncoderSetParallelRunner (JxlEncoder *enc, JxlParallelRunner parallel_runner, void *parallel_runner_opaque)
JXL_EXPORT JxlEncoderError | JxlEncoderGetError (JxlEncoder *enc)
JXL_EXPORT JxlEncoderStatus | JxlEncoderProcessOutput (JxlEncoder *enc, uint8_t **next_out, size_t *avail_out)
JXL_EXPORT JxlEncoderStatus | JxlEncoderSetFrameHeader (JxlEncoderFrameSettings *frame_settings, const JxlFrameHeader *frame_header)
JXL_EXPORT JxlEncoderStatus | JxlEncoderSetExtraChannelBlendInfo (JxlEncoderFrameSettings *frame_settings, size_t index, const JxlBlendInfo *blend_info)
JXL_EXPORT JxlEncoderStatus | JxlEncoderSetFrameName (JxlEncoderFrameSettings *frame_settings, const char *frame_name)
JXL_EXPORT JxlEncoderStatus | JxlEncoderSetFrameBitDepth (JxlEncoderFrameSettings *frame_settings, const JxlBitDepth *bit_depth)
JXL_EXPORT JxlEncoderStatus | JxlEncoderAddJPEGFrame (const JxlEncoderFrameSettings *frame_settings, const uint8_t *buffer, size_t size)
JXL_EXPORT JxlEncoderStatus | JxlEncoderAddImageFrame (const JxlEncoderFrameSettings *frame_settings, const JxlPixelFormat *pixel_format, const void *buffer, size_t size)
JXL_EXPORT JxlEncoderStatus | JxlEncoderSetOutputProcessor (JxlEncoder *enc, struct JxlEncoderOutputProcessor output_processor)
JXL_EXPORT JxlEncoderStatus | JxlEncoderFlushInput (JxlEncoder *enc)
JXL_EXPORT JxlEncoderStatus | JxlEncoderAddChunkedFrame (const JxlEncoderFrameSettings *frame_settings, JXL_BOOL is_last_frame, struct JxlChunkedFrameInputSource chunked_frame_input)
| Adds a frame to the encoder using a chunked input source.
JXL_EXPORT JxlEncoderStatus | JxlEncoderSetExtraChannelBuffer (const JxlEncoderFrameSettings *frame_settings, const JxlPixelFormat *pixel_format, const void *buffer, size_t size, uint32_t index)
JXL_EXPORT JxlEncoderStatus | JxlEncoderAddBox (JxlEncoder *enc, const JxlBoxType type, const uint8_t *contents, size_t size, JXL_BOOL compress_box)
JXL_EXPORT JxlEncoderStatus | JxlEncoderUseBoxes (JxlEncoder *enc)
JXL_EXPORT void | JxlEncoderCloseBoxes (JxlEncoder *enc)
JXL_EXPORT void | JxlEncoderCloseFrames (JxlEncoder *enc)
JXL_EXPORT void | JxlEncoderCloseInput (JxlEncoder *enc)
JXL_EXPORT JxlEncoderStatus | JxlEncoderSetColorEncoding (JxlEncoder *enc, const JxlColorEncoding *color)
JXL_EXPORT JxlEncoderStatus | JxlEncoderSetICCProfile (JxlEncoder *enc, const uint8_t *icc_profile, size_t size)
JXL_EXPORT void | JxlEncoderInitBasicInfo (JxlBasicInfo *info)
JXL_EXPORT void | JxlEncoderInitFrameHeader (JxlFrameHeader *frame_header)
JXL_EXPORT void | JxlEncoderInitBlendInfo (JxlBlendInfo *blend_info)
JXL_EXPORT JxlEncoderStatus | JxlEncoderSetBasicInfo (JxlEncoder *enc, const JxlBasicInfo *info)
JXL_EXPORT JxlEncoderStatus | JxlEncoderSetUpsamplingMode (JxlEncoder *enc, int64_t factor, int64_t mode)
JXL_EXPORT void | JxlEncoderInitExtraChannelInfo (JxlExtraChannelType type, JxlExtraChannelInfo *info)
JXL_EXPORT JxlEncoderStatus | JxlEncoderSetExtraChannelInfo (JxlEncoder *enc, size_t index, const JxlExtraChannelInfo *info)
JXL_EXPORT JxlEncoderStatus | JxlEncoderSetExtraChannelName (JxlEncoder *enc, size_t index, const char *name, size_t size)
JXL_EXPORT JxlEncoderStatus | JxlEncoderFrameSettingsSetOption (JxlEncoderFrameSettings *frame_settings, JxlEncoderFrameSettingId option, int64_t value)
JXL_EXPORT JxlEncoderStatus | JxlEncoderFrameSettingsSetFloatOption (JxlEncoderFrameSettings *frame_settings, JxlEncoderFrameSettingId option, float value)
JXL_EXPORT JxlEncoderStatus | JxlEncoderUseContainer (JxlEncoder *enc, JXL_BOOL use_container)
JXL_EXPORT JxlEncoderStatus | JxlEncoderStoreJPEGMetadata (JxlEncoder *enc, JXL_BOOL store_jpeg_metadata)
JXL_EXPORT JxlEncoderStatus | JxlEncoderSetCodestreamLevel (JxlEncoder *enc, int level)
JXL_EXPORT int | JxlEncoderGetRequiredCodestreamLevel (const JxlEncoder *enc)
JXL_EXPORT JxlEncoderStatus | JxlEncoderSetFrameLossless (JxlEncoderFrameSettings *frame_settings, JXL_BOOL lossless)
JXL_EXPORT JxlEncoderStatus | JxlEncoderSetFrameDistance (JxlEncoderFrameSettings *frame_settings, float distance)
JXL_EXPORT JxlEncoderStatus | JxlEncoderSetExtraChannelDistance (JxlEncoderFrameSettings *frame_settings, size_t index, float distance)
JXL_EXPORT float | JxlEncoderDistanceFromQuality (float quality)
JXL_EXPORT JxlEncoderFrameSettings * | JxlEncoderFrameSettingsCreate (JxlEncoder *enc, const JxlEncoderFrameSettings *source)
JXL_EXPORT void | JxlColorEncodingSetToSRGB (JxlColorEncoding *color_encoding, JXL_BOOL is_gray)
JXL_EXPORT void | JxlColorEncodingSetToLinearSRGB (JxlColorEncoding *color_encoding, JXL_BOOL is_gray)
JXL_EXPORT void | JxlEncoderAllowExpertOptions (JxlEncoder *enc)
JXL_EXPORT void | JxlEncoderSetDebugImageCallback (JxlEncoderFrameSettings *frame_settings, JxlDebugImageCallback callback, void *opaque)
JXL_EXPORT void | JxlEncoderCollectStats (JxlEncoderFrameSettings *frame_settings, JxlEncoderStats *stats)
JXL_EXPORT JxlEncoderStats * | JxlEncoderStatsCreate (void)
JXL_EXPORT void | JxlEncoderStatsDestroy (JxlEncoderStats *stats)
JXL_EXPORT size_t | JxlEncoderStatsGet (const JxlEncoderStats *stats, JxlEncoderStatsKey key)
JXL_EXPORT void | JxlEncoderStatsMerge (JxlEncoderStats *stats, const JxlEncoderStats *other)

## Detailed Description

## Typedef Documentation

## ◆ JxlDebugImageCallback

typedef void(* JxlDebugImageCallback) (void *opaque, const char *label, size_t xsize, size_t ysize, const JxlColorEncoding *color, const uint16_t *pixels)

Function type for JxlEncoderSetDebugImageCallback.

The callback may be called simultaneously by different threads when using a threaded parallel runner, on different debug images.

Parameters

  opaque | optional user data, as given to JxlEncoderSetDebugImageCallback.
  label | label of debug image, can be used in filenames
  xsize | width of debug image
  ysize | height of debug image
  color | color encoding of debug image
  pixels | pixel data of debug image as big-endian 16-bit unsigned samples. The memory is not owned by the user, and is only valid during the time the callback is running.

## ◆ JxlEncoder

typedef struct JxlEncoderStruct JxlEncoder

Opaque structure that holds the JPEG XL encoder.

Allocated and initialized with JxlEncoderCreate(). Cleaned up and deallocated with JxlEncoderDestroy().

## ◆ JxlEncoderFrameSettings

typedef struct JxlEncoderFrameSettingsStruct JxlEncoderFrameSettings

Settings and metadata for a single image frame. This includes encoder options for a frame such as compression quality and speed.

Allocated and initialized with JxlEncoderFrameSettingsCreate(). Cleaned up and deallocated when the encoder is destroyed with JxlEncoderDestroy().

## ◆ JxlEncoderStats

typedef struct JxlEncoderStatsStruct JxlEncoderStats

Opaque structure that holds the encoder statistics.

Allocated and initialized with JxlEncoderStatsCreate(). Cleaned up and deallocated with JxlEncoderStatsDestroy().

## Enumeration Type Documentation

## ◆ JxlEncoderError

enum JxlEncoderError

Error conditions: API usage errors have the 0x80 bit set to 1 Other errors have the 0x80 bit set to 0

Enumerator
JXL_ENC_ERR_OK | No error
JXL_ENC_ERR_GENERIC | Generic encoder error due to unspecified cause
JXL_ENC_ERR_OOM | Out of memory TODO(jon): actually catch this and return this error
JXL_ENC_ERR_JBRD | JPEG bitstream reconstruction data could not be represented (e.g. too much tail data)
JXL_ENC_ERR_BAD_INPUT | Input is invalid (e.g. corrupt JPEG file or ICC profile)
JXL_ENC_ERR_NOT_SUPPORTED | The encoder doesn't (yet) support this. Either no version of libjxl supports this, and the API is used incorrectly, or the libjxl version should have been checked before trying to do this.
JXL_ENC_ERR_API_USAGE | The encoder API is used in an incorrect way. In this case, a debug build of libjxl should output a specific error message. (if not, please open an issue about it)

## ◆ JxlEncoderFrameSettingId

enum JxlEncoderFrameSettingId

Id of encoder options for a frame. This includes options such as setting encoding effort/speed or overriding the use of certain coding tools, for this frame. This does not include non-frame related encoder options such as for boxes.

Enumerator
JXL_ENC_FRAME_SETTING_EFFORT | Sets encoder effort/speed level without affecting decoding speed. Valid values are, from faster to slower speed: 1:lightning 2:thunder 3:falcon 4:cheetah 5:hare 6:wombat 7:squirrel 8:kitten 9:tortoise. Default: squirrel (7).
JXL_ENC_FRAME_SETTING_DECODING_SPEED | Sets the decoding speed tier for the provided options. Minimum is 0 (slowest to decode, best quality/density), and maximum is 4 (fastest to decode, at the cost of some quality/density). Default is 0.
JXL_ENC_FRAME_SETTING_RESAMPLING | Sets resampling option. If enabled, the image is downsampled before compression, and upsampled to original size in the decoder. Integer option, use -1 for the default behavior (resampling only applied for low quality), 1 for no downsampling (1x1), 2 for 2x2 downsampling, 4 for 4x4 downsampling, 8 for 8x8 downsampling.
JXL_ENC_FRAME_SETTING_EXTRA_CHANNEL_RESAMPLING | Similar to JXL_ENC_FRAME_SETTING_RESAMPLING, but for extra channels. Integer option, use -1 for the default behavior (depends on encoder implementation), 1 for no downsampling (1x1), 2 for 2x2 downsampling, 4 for 4x4 downsampling, 8 for 8x8 downsampling.
JXL_ENC_FRAME_SETTING_ALREADY_DOWNSAMPLED | Indicates the frame added with JxlEncoderAddImageFrame is already downsampled by the downsampling factor set with JXL_ENC_FRAME_SETTING_RESAMPLING. The input frame must then be given in the downsampled resolution, not the full image resolution. The downsampled resolution is given by ceil(xsize / resampling), ceil(ysize / resampling) with xsize and ysize the dimensions given in the basic info, and resampling the factor set with JXL_ENC_FRAME_SETTING_RESAMPLING. Use 0 to disable, 1 to enable. Default value is 0.
JXL_ENC_FRAME_SETTING_PHOTON_NOISE | Adds noise to the image emulating photographic film noise, the higher the given number, the grainier the image will be. As an example, a value of 100 gives low noise whereas a value of 3200 gives a lot of noise. The default value is 0.
JXL_ENC_FRAME_SETTING_NOISE | Enables adaptive noise generation. This setting is not recommended for use, please use JXL_ENC_FRAME_SETTING_PHOTON_NOISE instead. Use -1 for the default (encoder chooses), 0 to disable, 1 to enable.
JXL_ENC_FRAME_SETTING_DOTS | Enables or disables dots generation. Use -1 for the default (encoder chooses), 0 to disable, 1 to enable.
JXL_ENC_FRAME_SETTING_PATCHES | Enables or disables patches generation. Use -1 for the default (encoder chooses), 0 to disable, 1 to enable.
JXL_ENC_FRAME_SETTING_EPF | Edge preserving filter level, -1 to 3. Use -1 for the default (encoder chooses), 0 to 3 to set a strength.
JXL_ENC_FRAME_SETTING_GABORISH | Enables or disables the gaborish filter. Use -1 for the default (encoder chooses), 0 to disable, 1 to enable.
JXL_ENC_FRAME_SETTING_MODULAR | Enables modular encoding. Use -1 for default (encoder chooses), 0 to enforce VarDCT mode (e.g. for photographic images), 1 to enforce modular mode (e.g. for lossless images).
JXL_ENC_FRAME_SETTING_KEEP_INVISIBLE | Enables or disables preserving color of invisible pixels. Use -1 for the default (1 if lossless, 0 if lossy), 0 to disable, 1 to enable.
JXL_ENC_FRAME_SETTING_GROUP_ORDER | Determines the order in which 256x256 regions are stored in the codestream for progressive rendering. Use -1 for the encoder default, 0 for scanline order, 1 for center-first order.
JXL_ENC_FRAME_SETTING_GROUP_ORDER_CENTER_X | Determines the horizontal position of center for the center-first group order. Use -1 to automatically use the middle of the image, 0..xsize to specifically set it.
JXL_ENC_FRAME_SETTING_GROUP_ORDER_CENTER_Y | Determines the center for the center-first group order. Use -1 to automatically use the middle of the image, 0..ysize to specifically set it.
JXL_ENC_FRAME_SETTING_RESPONSIVE | Enables or disables progressive encoding for modular mode. Use -1 for the encoder default, 0 to disable, 1 to enable.
JXL_ENC_FRAME_SETTING_PROGRESSIVE_AC | Set the progressive mode for the AC coefficients of VarDCT, using spectral progression from the DCT coefficients. Use -1 for the encoder default, 0 to disable, 1 to enable.
JXL_ENC_FRAME_SETTING_QPROGRESSIVE_AC | Set the progressive mode for the AC coefficients of VarDCT, using quantization of the least significant bits. Use -1 for the encoder default, 0 to disable, 1 to enable.
JXL_ENC_FRAME_SETTING_PROGRESSIVE_DC | Set the progressive mode using lower-resolution DC images for VarDCT. Use -1 for the encoder default, 0 to disable, 1 to have an extra 64x64 lower resolution pass, 2 to have a 512x512 and 64x64 lower resolution pass.
JXL_ENC_FRAME_SETTING_CHANNEL_COLORS_GLOBAL_PERCENT | Use Global channel palette if the amount of colors is smaller than this percentage of range. Use 0-100 to set an explicit percentage, -1 to use the encoder default. Used for modular encoding.
JXL_ENC_FRAME_SETTING_CHANNEL_COLORS_GROUP_PERCENT | Use Local (per-group) channel palette if the amount of colors is smaller than this percentage of range. Use 0-100 to set an explicit percentage, -1 to use the encoder default. Used for modular encoding.
JXL_ENC_FRAME_SETTING_PALETTE_COLORS | Use color palette if amount of colors is smaller than or equal to this amount, or -1 to use the encoder default. Used for modular encoding.
JXL_ENC_FRAME_SETTING_LOSSY_PALETTE | Enables or disables delta palette. Use -1 for the default (encoder chooses), 0 to disable, 1 to enable. Used in modular mode.
JXL_ENC_FRAME_SETTING_COLOR_TRANSFORM | Color transform for internal encoding: -1 = default, 0=XYB, 1=none (RGB), 2=YCbCr. The XYB setting performs the forward XYB transform. None and YCbCr both perform no transform, but YCbCr is used to indicate that the encoded data losslessly represents YCbCr values.
JXL_ENC_FRAME_SETTING_MODULAR_COLOR_SPACE | Reversible color transform for modular encoding: -1=default, 0-41=RCT index, e.g. index 0 = none, index 6 = YCoCg. If this option is set to a non-default value, the RCT will be globally applied to the whole frame. The default behavior is to try several RCTs locally per modular group, depending on the speed and distance setting.
JXL_ENC_FRAME_SETTING_MODULAR_GROUP_SIZE | Group size for modular encoding: -1=default, 0=128, 1=256, 2=512, 3=1024.
JXL_ENC_FRAME_SETTING_MODULAR_PREDICTOR | Predictor for modular encoding. -1 = default, 0=zero, 1=left, 2=top, 3=avg0, 4=select, 5=gradient, 6=weighted, 7=topright, 8=topleft, 9=leftleft, 10=avg1, 11=avg2, 12=avg3, 13=toptop predictive average 14=mix 5 and 6, 15=mix everything.
JXL_ENC_FRAME_SETTING_MODULAR_MA_TREE_LEARNING_PERCENT | Fraction of pixels used to learn MA trees as a percentage. -1 = default, 0 = no MA and fast decode, 50 = default value, 100 = all, values above 100 are also permitted. Higher values use more encoder memory.
JXL_ENC_FRAME_SETTING_MODULAR_NB_PREV_CHANNELS | Number of extra (previous-channel) MA tree properties to use. -1 = default, 0-11 = valid values. Recommended values are in the range 0 to 3, or 0 to amount of channels minus 1 (including all extra channels, and excluding color channels when using VarDCT mode). Higher value gives slower encoding and slower decoding.
JXL_ENC_FRAME_SETTING_JPEG_RECON_CFL | Enable or disable CFL (chroma-from-luma) for lossless JPEG recompression. -1 = default, 0 = disable CFL, 1 = enable CFL.
JXL_ENC_FRAME_INDEX_BOX | Prepare the frame for indexing in the frame index box. 0 = ignore this frame (same as not setting a value), 1 = index this frame within the Frame Index Box. If any frames are indexed, the first frame needs to be indexed, too. If the first frame is not indexed, and a later frame is attempted to be indexed, JXL_ENC_ERROR will occur. If non-keyframes, i.e., frames with cropping, blending or patches are attempted to be indexed, JXL_ENC_ERROR will occur.
JXL_ENC_FRAME_SETTING_BROTLI_EFFORT | Sets brotli encode effort for use in JPEG recompression and compressed metadata boxes (brob). Can be -1 (default) or 0 (fastest) to 11 (slowest). Default is based on the general encode effort in case of JPEG recompression, and 4 for brob boxes.
JXL_ENC_FRAME_SETTING_JPEG_COMPRESS_BOXES | Enables or disables brotli compression of metadata boxes derived from a JPEG frame when using JxlEncoderAddJPEGFrame. This has no effect on boxes added using JxlEncoderAddBox. -1 = default, 0 = disable compression, 1 = enable compression.
JXL_ENC_FRAME_SETTING_BUFFERING | Control what kind of buffering is used, when using chunked image frames. -1 = default (let the encoder decide) 0 = buffers everything, basically the same as non-streamed code path (mainly for testing) 1 = buffers everything for images that are smaller than 2048 x 2048, and uses streaming input and output for larger images 2 = uses streaming input and output for all images that are larger than one group, i.e. 256 x 256 pixels by default 3 = currently same as 2 When using streaming input and output the encoder minimizes memory usage at the cost of compression density. Also note that images produced with streaming mode might not be progressively decodeable.
JXL_ENC_FRAME_SETTING_JPEG_KEEP_EXIF | Keep or discard Exif metadata boxes derived from a JPEG frame when using JxlEncoderAddJPEGFrame. This has no effect on boxes added using JxlEncoderAddBox. When JxlEncoderStoreJPEGMetadata is set to 1, this option cannot be set to 0. Even when Exif metadata is discarded, the orientation will still be applied. 0 = discard Exif metadata, 1 = keep Exif metadata (default).
JXL_ENC_FRAME_SETTING_JPEG_KEEP_XMP | Keep or discard XMP metadata boxes derived from a JPEG frame when using JxlEncoderAddJPEGFrame. This has no effect on boxes added using JxlEncoderAddBox. When JxlEncoderStoreJPEGMetadata is set to 1, this option cannot be set to 0. 0 = discard XMP metadata, 1 = keep XMP metadata (default).
JXL_ENC_FRAME_SETTING_JPEG_KEEP_JUMBF | Keep or discard JUMBF metadata boxes derived from a JPEG frame when using JxlEncoderAddJPEGFrame. This has no effect on boxes added using JxlEncoderAddBox. 0 = discard JUMBF metadata, 1 = keep JUMBF metadata (default).
JXL_ENC_FRAME_SETTING_USE_FULL_IMAGE_HEURISTICS | If this mode is disabled, the encoder will not make any image quality decisions that are computed based on the full image, but stored only once (e.g. the X quant multiplier in the frame header). Used mainly for testing equivalence of streaming and non-streaming code. 0 = disabled, 1 = enabled (default)
JXL_ENC_FRAME_SETTING_FILL_ENUM | Enum value not to be used as an option. This value is added to force the C compiler to have the enum to take a known size.

## ◆ JxlEncoderStatsKey

enum JxlEncoderStatsKey

Data type for querying JxlEncoderStats object

## ◆ JxlEncoderStatus

enum JxlEncoderStatus

Return value for multiple encoder functions.

Enumerator
JXL_ENC_SUCCESS | Function call finished successfully, or encoding is finished and there is nothing more to be done.
JXL_ENC_ERROR | An error occurred, for example out of memory.
JXL_ENC_NEED_MORE_OUTPUT | The encoder needs more output buffer to continue encoding.

## Function Documentation

## ◆ JxlColorEncodingSetToLinearSRGB()

JXL_EXPORT void JxlColorEncodingSetToLinearSRGB | ( | JxlColorEncoding * | color_encoding,
|  | JXL_BOOL | is_gray )

Sets a color encoding to be linear sRGB.

Parameters

  color_encoding | color encoding instance.
  is_gray | whether the color encoding should be gray scale or color.

## ◆ JxlColorEncodingSetToSRGB()

JXL_EXPORT void JxlColorEncodingSetToSRGB | ( | JxlColorEncoding * | color_encoding,
|  | JXL_BOOL | is_gray )

Sets a color encoding to be sRGB.

Parameters

  color_encoding | color encoding instance.
  is_gray | whether the color encoding should be gray scale or color.

## ◆ JxlEncoderAddBox()

JXL_EXPORT JxlEncoderStatus JxlEncoderAddBox | ( | JxlEncoder * | enc,
|  | const JxlBoxType | type,
|  | const uint8_t * | contents,
|  | size_t | size,
|  | JXL_BOOL | compress_box )

Adds a metadata box to the file format. JxlEncoderProcessOutput must be used to effectively write the box to the output. JxlEncoderUseBoxes must be enabled before using this function.

Boxes allow inserting application-specific data and metadata (Exif, XML/XMP, JUMBF and user defined boxes).

The box format follows ISO BMFF and shares features and box types with other image and video formats, including the Exif, XML and JUMBF boxes. The box format for JPEG XL is specified in ISO/IEC 18181-2.

Boxes in general don't contain other boxes inside, except a JUMBF superbox. Boxes follow each other sequentially and are byte-aligned. If the container format is used, the JXL stream consists of concatenated boxes. It is also possible to use a direct codestream without boxes, but in that case metadata cannot be added.

Each box generally has the following byte structure in the file:

- 4 bytes: box size including box header (Big endian. If set to 0, an 8-byte 64-bit size follows instead).
- 4 bytes: type, e.g. "JXL " for the signature box, "jxlc" for a codestream box.
- N bytes: box contents.

Only the box contents are provided to the contents argument of this function, the encoder encodes the size header itself. Most boxes are written automatically by the encoder as needed ("JXL ", "ftyp", "jxll", "jxlc", "jxlp", "jxli", "jbrd"), and this function only needs to be called to add optional metadata when encoding from pixels (using JxlEncoderAddImageFrame). When recompressing JPEG files (using JxlEncoderAddJPEGFrame), if the input JPEG contains EXIF, XMP or JUMBF metadata, the corresponding boxes are already added automatically.

Box types are given by 4 characters. The following boxes can be added with this function:

- "Exif": a box with EXIF metadata, can be added by libjxl users, or is automatically added when needed for JPEG reconstruction. The contents of this box must be prepended by a 4-byte tiff header offset, which may be 4 zero bytes in case the tiff header follows immediately. The EXIF metadata must be in sync with what is encoded in the JPEG XL codestream, specifically the image orientation. While this is not recommended in practice, in case of conflicting metadata, the JPEG XL codestream takes precedence.
- "xml ": a box with XML data, in particular XMP metadata, can be added by libjxl users, or is automatically added when needed for JPEG reconstruction
- "jumb": a JUMBF superbox, which can contain boxes with different types of metadata inside. This box type can be added by the encoder transparently, and other libraries to create and handle JUMBF content exist.
- Application-specific boxes. Their typename should not begin with "jxl" or "JXL" or conflict with other existing typenames, and they should be registered with MP4RA (mp4ra.org).

These boxes can be stored uncompressed or Brotli-compressed (using a "brob" box), depending on the compress_box parameter.

Parameters

  enc | encoder object.
  type | the box type, e.g. "Exif" for EXIF metadata, "xml " for XMP or IPTC metadata, "jumb" for JUMBF metadata.
  contents | the full contents of the box, for example EXIF data. ISO BMFF box header must not be included, only the contents. Owned by the caller and its contents are copied internally.
  size | size of the box contents.
  compress_box | Whether to compress this box as a "brob" box. Requires Brotli support.

Returns
  JXL_ENC_SUCCESS on success, JXL_ENC_ERROR on error, such as when using this function without JxlEncoderUseContainer, or adding a box type that would result in an invalid file format.

## ◆ JxlEncoderAddChunkedFrame()

JXL_EXPORT JxlEncoderStatus JxlEncoderAddChunkedFrame | ( | const JxlEncoderFrameSettings * | frame_settings,
|  | JXL_BOOL | is_last_frame,
|  | struct JxlChunkedFrameInputSource | chunked_frame_input )

Adds a frame to the encoder using a chunked input source.

This function gives a way to encode a frame by providing pixel data in a chunked or streaming manner, which can be especially useful when dealing with large images that may not fit entirely in memory or when trying to optimize memory usage. The input data is provided through callbacks defined in the JxlChunkedFrameInputSource struct. Once the frame data has been completely retrieved, this function will flush the input and close it if it is the last frame.

Parameters

  frame_settings | set of options and metadata for this frame. Also includes reference to the encoder object.
  is_last_frame | indicates if this is the last frame.
  chunked_frame_input | struct providing callback methods for retrieving pixel data in chunks.

Returns
  Returns a status indicating the success or failure of adding the frame.

## ◆ JxlEncoderAddImageFrame()

JXL_EXPORT JxlEncoderStatus JxlEncoderAddImageFrame | ( | const JxlEncoderFrameSettings * | frame_settings,
|  | const JxlPixelFormat * | pixel_format,
|  | const void * | buffer,
|  | size_t | size )

Sets the buffer to read pixels from for the next image to encode. Must call JxlEncoderSetBasicInfo before JxlEncoderAddImageFrame.

Currently only some data types for pixel formats are supported:

- JXL_TYPE_UINT8, with range 0..255
- JXL_TYPE_UINT16, with range 0..65535
- JXL_TYPE_FLOAT16, with nominal range 0..1
- JXL_TYPE_FLOAT, with nominal range 0..1

Note: the sample data type in pixel_format is allowed to be different from what is described in the JxlBasicInfo. The type in pixel_format, together with an optional JxlBitDepth parameter set by JxlEncoderSetFrameBitDepth describes the format of the uncompressed pixel buffer. The bits_per_sample and exponent_bits_per_sample in the JxlBasicInfo describes what will actually be encoded in the JPEG XL codestream. For example, to encode a 12-bit image, you would set bits_per_sample to 12, while the input frame buffer can be in the following formats:

- if pixel format is in JXL_TYPE_UINT16 with default bit depth setting (i.e. JXL_BIT_DEPTH_FROM_PIXEL_FORMAT), input sample values are rescaled to 16-bit, i.e. multiplied by 65535/4095;
- if pixel format is in JXL_TYPE_UINT16 with JXL_BIT_DEPTH_FROM_CODESTREAM bit depth setting, input sample values are provided unscaled;
- if pixel format is in JXL_TYPE_FLOAT, input sample values are rescaled to 0..1, i.e. multiplied by 1.f/4095.f. While it is allowed, it is obviously not recommended to use a pixel_format with lower precision than what is specified in the JxlBasicInfo.

We support interleaved channels as described by the JxlPixelFormat:

- single-channel data, e.g. grayscale
- single-channel + alpha
- trichromatic, e.g. RGB
- trichromatic + alpha

Extra channels not handled here need to be set by JxlEncoderSetExtraChannelBuffer. If the image has alpha, and alpha is not passed here, it will implicitly be set to all-opaque (an alpha value of 1.0 everywhere).

The pixels are assumed to be encoded in the original profile that is set with JxlEncoderSetColorEncoding or JxlEncoderSetICCProfile. If none of these functions were used, the pixels are assumed to be nonlinear sRGB for integer data types (JXL_TYPE_UINT8, JXL_TYPE_UINT16), and linear sRGB for floating point data types (JXL_TYPE_FLOAT16, JXL_TYPE_FLOAT).

Sample values in floating-point pixel formats are allowed to be outside the nominal range, e.g. to represent out-of-sRGB-gamut colors in the uses_original_profile=false case. They are however not allowed to be NaN or +-infinity.

If this is the last frame, JxlEncoderCloseInput or JxlEncoderCloseFrames must be called before the next JxlEncoderProcessOutput call.

Parameters

  frame_settings | set of options and metadata for this frame. Also includes reference to the encoder object.
  pixel_format | format for pixels. Object owned by the caller and its contents are copied internally.
  buffer | buffer type to input the pixel data from. Owned by the caller and its contents are copied internally.
  size | size of buffer in bytes. This size should match what is implied by the frame dimensions and the pixel format.

Returns
  JXL_ENC_SUCCESS on success, JXL_ENC_ERROR on error

## ◆ JxlEncoderAddJPEGFrame()

JXL_EXPORT JxlEncoderStatus JxlEncoderAddJPEGFrame | ( | const JxlEncoderFrameSettings * | frame_settings,
|  | const uint8_t * | buffer,
|  | size_t | size )

Sets the buffer to read JPEG encoded bytes from for the next frame to encode.

If JxlEncoderSetBasicInfo has not yet been called, calling JxlEncoderAddJPEGFrame will implicitly call it with the parameters of the added JPEG frame.

If JxlEncoderSetColorEncoding or JxlEncoderSetICCProfile has not yet been called, calling JxlEncoderAddJPEGFrame will implicitly call it with the parameters of the added JPEG frame.

If the encoder is set to store JPEG reconstruction metadata using JxlEncoderStoreJPEGMetadata and a single JPEG frame is added, it will be possible to losslessly reconstruct the JPEG codestream.

If this is the last frame, JxlEncoderCloseInput or JxlEncoderCloseFrames must be called before the next JxlEncoderProcessOutput call.

Note, this can only be used to add JPEG frames for lossless compression. To encode with lossy compression, the JPEG must be decoded manually and a pixel buffer added using JxlEncoderAddImageFrame.

Parameters

  frame_settings | set of options and metadata for this frame. Also includes reference to the encoder object.
  buffer | bytes to read JPEG from. Owned by the caller and its contents are copied internally.
  size | size of buffer in bytes.

Returns
  JXL_ENC_SUCCESS on success, JXL_ENC_ERROR on error

## ◆ JxlEncoderAllowExpertOptions()

JXL_EXPORT void JxlEncoderAllowExpertOptions | ( | JxlEncoder * | enc | ) |

Enables usage of expert options.

At the moment, the only expert option is setting an effort value of 10, which gives the best compression for pixel-lossless modes but is very slow.

Parameters

  enc | encoder object.

## ◆ JxlEncoderCloseBoxes()

JXL_EXPORT void JxlEncoderCloseBoxes | ( | JxlEncoder * | enc | ) |

Declares that no further boxes will be added with JxlEncoderAddBox. This function must be called after the last box is added so the encoder knows the stream will be finished. It is not necessary to use this function if JxlEncoderUseBoxes is not used. Further frames may still be added.

Must be called between JxlEncoderAddBox of the last box and the next call to JxlEncoderProcessOutput, or JxlEncoderProcessOutput won't output the last box correctly.

NOTE: if you don't need to close frames and boxes at separate times, you can use JxlEncoderCloseInput instead to close both at once.

Parameters

  enc | encoder object.

## ◆ JxlEncoderCloseFrames()

JXL_EXPORT void JxlEncoderCloseFrames | ( | JxlEncoder * | enc | ) |

Declares that no frames will be added and JxlEncoderAddImageFrame and JxlEncoderAddJPEGFrame won't be called anymore. Further metadata boxes may still be added. This function or JxlEncoderCloseInput must be called after adding the last frame and the next call to JxlEncoderProcessOutput, or the frame won't be properly marked as last.

NOTE: if you don't need to close frames and boxes at separate times, you can use JxlEncoderCloseInput instead to close both at once.

Parameters

  enc | encoder object.

## ◆ JxlEncoderCloseInput()

JXL_EXPORT void JxlEncoderCloseInput | ( | JxlEncoder * | enc | ) |

Closes any input to the encoder, equivalent to calling JxlEncoderCloseFrames as well as calling JxlEncoderCloseBoxes if needed. No further input of any kind may be given to the encoder, but further JxlEncoderProcessOutput calls should be done to create the final output.

The requirements of both JxlEncoderCloseFrames and JxlEncoderCloseBoxes apply to this function. Either this function or the other two must be called after the final frame and/or box, and the next JxlEncoderProcessOutput call, or the codestream won't be encoded correctly.

Parameters

  enc | encoder object.

## ◆ JxlEncoderCollectStats()

JXL_EXPORT void JxlEncoderCollectStats | ( | JxlEncoderFrameSettings * | frame_settings,
|  | JxlEncoderStats * | stats )

Sets the given stats object for gathering various statistics during encoding.

This only has any effect if the encoder was compiled with the appropriate debug build flags.

Parameters

  frame_settings | set of options and metadata for this frame. Also includes reference to the encoder object.
  stats | object that can be used to query the gathered stats (created by JxlEncoderStatsCreate)

## ◆ JxlEncoderCreate()

JXL_EXPORT JxlEncoder * JxlEncoderCreate | ( | const JxlMemoryManager * | memory_manager | ) |

Creates an instance of JxlEncoder and initializes it.

`memory_manager` will be used for all the library dynamic allocations made from this instance. The parameter may be NULL, in which case the default allocator will be used. See jpegxl/memory_manager.h for details.

Parameters

  memory_manager | custom allocator function. It may be NULL. The memory manager will be copied internally.

Returns
  `NULL` if the instance can not be allocated or initialized
  pointer to initialized JxlEncoder otherwise

## ◆ JxlEncoderDestroy()

JXL_EXPORT void JxlEncoderDestroy | ( | JxlEncoder * | enc | ) |

Deinitializes and frees a JxlEncoder instance.

Parameters

  enc | instance to be cleaned up and deallocated.

## ◆ JxlEncoderDistanceFromQuality()

JXL_EXPORT float JxlEncoderDistanceFromQuality | ( | float | quality | ) |

Maps JPEG-style quality factor to distance.

This function takes in input a JPEG-style quality factor `quality` and produces as output a `distance` value suitable to be used with JxlEncoderSetFrameDistance and JxlEncoderSetExtraChannelDistance.

The `distance` value influences the level of compression, with lower values indicating higher quality:

- 0.0 implies lossless compression (however, note that calling JxlEncoderSetFrameLossless is required).
- 1.0 represents a visually lossy compression, which is also the default setting.

The `quality` parameter, ranging up to 100, is inversely related to 'distance':

- A `quality` of 100.0 maps to a `distance` of 0.0 (lossless).
- A `quality` of 90.0 corresponds to a `distance` of 1.0.

Recommended Range:

- `distance`: 0.5 to 3.0.
- corresponding `quality`: approximately 96 to 68.

Allowed Range:

- `distance`: 0.0 to 25.0.
- corresponding `quality`: 100.0 to 0.0.

Note: the `quality` parameter has no consistent psychovisual meaning across different codecs and libraries. Using the mapping defined by JxlEncoderDistanceFromQuality will result in a visual quality roughly equivalent to what would be obtained with `libjpeg-turbo` with the same `quality` parameter, but that is by no means guaranteed; do not assume that the same quality value will result in similar file sizes and image quality across different codecs.

## ◆ JxlEncoderFlushInput()

JXL_EXPORT JxlEncoderStatus JxlEncoderFlushInput | ( | JxlEncoder * | enc | ) |

Flushes any buffered input in the encoder, ensuring that all available input data has been processed and written to the output.

This function can only be used after JxlEncoderSetOutputProcessor. Before making the last call to JxlEncoderFlushInput, users should call JxlEncoderCloseInput to signal the end of input data.

This should not be used when using JxlEncoderProcessOutput.

Parameters

  enc | encoder object.

Returns
  JXL_ENC_SUCCESS on success, JXL_ENC_ERROR on error.

## ◆ JxlEncoderFrameSettingsCreate()

JXL_EXPORT JxlEncoderFrameSettings * JxlEncoderFrameSettingsCreate | ( | JxlEncoder * | enc,
|  | const JxlEncoderFrameSettings * | source )

Create a new set of encoder options, with all values initially copied from the `source` options, or set to default if `source` is NULL.

The returned pointer is an opaque struct tied to the encoder and it will be deallocated by the encoder when JxlEncoderDestroy() is called. For functions taking both a JxlEncoder and a JxlEncoderFrameSettings, only JxlEncoderFrameSettings created with this function for the same encoder instance can be used.

Parameters

  enc | encoder object.
  source | source options to copy initial values from, or NULL to get defaults initialized to defaults.

Returns
  the opaque struct pointer identifying a new set of encoder options.

## ◆ JxlEncoderFrameSettingsSetFloatOption()

JXL_EXPORT JxlEncoderStatus JxlEncoderFrameSettingsSetFloatOption | ( | JxlEncoderFrameSettings * | frame_settings,
|  | JxlEncoderFrameSettingId | option,
|  | float | value )

Sets a frame-specific option of float type to the encoder options. The JxlEncoderFrameSettingId argument determines which option is set.

Parameters

  frame_settings | set of options and metadata for this frame. Also includes reference to the encoder object.
  option | ID of the option to set.
  value | Float value to set for this option.

Returns
  JXL_ENC_SUCCESS if the operation was successful, JXL_ENC_ERROR in case of an error, such as invalid or unknown option id, or invalid integer value for the given option. If an error is returned, the state of the JxlEncoderFrameSettings object is still valid and is the same as before this function was called.

## ◆ JxlEncoderFrameSettingsSetOption()

JXL_EXPORT JxlEncoderStatus JxlEncoderFrameSettingsSetOption | ( | JxlEncoderFrameSettings * | frame_settings,
|  | JxlEncoderFrameSettingId | option,
|  | int64_t | value )

Sets a frame-specific option of integer type to the encoder options. The JxlEncoderFrameSettingId argument determines which option is set.

Parameters

  frame_settings | set of options and metadata for this frame. Also includes reference to the encoder object.
  option | ID of the option to set.
  value | Integer value to set for this option.

Returns
  JXL_ENC_SUCCESS if the operation was successful, JXL_ENC_ERROR in case of an error, such as invalid or unknown option id, or invalid integer value for the given option. If an error is returned, the state of the JxlEncoderFrameSettings object is still valid and is the same as before this function was called.

## ◆ JxlEncoderGetError()

JXL_EXPORT JxlEncoderError JxlEncoderGetError | ( | JxlEncoder * | enc | ) |

Get the (last) error code in case JXL_ENC_ERROR was returned.

Parameters

  enc | encoder object.

Returns
  the JxlEncoderError that caused the (last) JXL_ENC_ERROR to be returned.

## ◆ JxlEncoderGetRequiredCodestreamLevel()

JXL_EXPORT int JxlEncoderGetRequiredCodestreamLevel | ( | const JxlEncoder * | enc | ) |

Returns the codestream level required to support the currently configured settings and basic info. This function can only be used at the beginning, before encoding starts, but after setting basic info.

This does not support per-frame settings, only global configuration, such as the image dimensions, that are known at the time of writing the header of the JPEG XL file.

If this returns 5, nothing needs to be done and the codestream can be compatible with any decoder. If this returns 10, JxlEncoderSetCodestreamLevel has to be used to set the codestream level to 10, or the encoder can be configured differently to allow using the more compatible level 5.

Parameters

  enc | encoder object.

Returns
  -1 if no level can support the configuration (e.g. image dimensions larger than even level 10 supports), 5 if level 5 is supported, 10 if setting the codestream level to 10 is required.

## ◆ JxlEncoderInitBasicInfo()

JXL_EXPORT void JxlEncoderInitBasicInfo | ( | JxlBasicInfo * | info | ) |

Initializes a JxlBasicInfo struct to default values. For forwards-compatibility, this function has to be called before values are assigned to the struct fields. The default values correspond to an 8-bit RGB image, no alpha or any other extra channels.

Parameters

  info | global image metadata. Object owned by the caller.

## ◆ JxlEncoderInitBlendInfo()

JXL_EXPORT void JxlEncoderInitBlendInfo | ( | JxlBlendInfo * | blend_info | ) |

Initializes a JxlBlendInfo struct to default values. For forwards-compatibility, this function has to be called before values are assigned to the struct fields.

Parameters

  blend_info | blending info. Object owned by the caller.

## ◆ JxlEncoderInitExtraChannelInfo()

JXL_EXPORT void JxlEncoderInitExtraChannelInfo | ( | JxlExtraChannelType | type,
|  | JxlExtraChannelInfo * | info )

Initializes a JxlExtraChannelInfo struct to default values. For forwards-compatibility, this function has to be called before values are assigned to the struct fields. The default values correspond to an 8-bit channel of the provided type.

Parameters

  type | type of the extra channel.
  info | global extra channel metadata. Object owned by the caller and its contents are copied internally.

## ◆ JxlEncoderInitFrameHeader()

JXL_EXPORT void JxlEncoderInitFrameHeader | ( | JxlFrameHeader * | frame_header | ) |

Initializes a JxlFrameHeader struct to default values. For forwards-compatibility, this function has to be called before values are assigned to the struct fields. The default values correspond to a frame with no animation duration and the 'replace' blend mode. After using this function, For animation duration must be set, for composite still blend settings must be set.

Parameters

  frame_header | frame metadata. Object owned by the caller.

## ◆ JxlEncoderProcessOutput()

JXL_EXPORT JxlEncoderStatus JxlEncoderProcessOutput | ( | JxlEncoder * | enc,
|  | uint8_t ** | next_out,
|  | size_t * | avail_out )

Encodes a JPEG XL file using the available bytes. `*avail_out` indicates how many output bytes are available, and `*next_out` points to the input bytes. *avail_out will be decremented by the amount of bytes that have been processed by the encoder and *next_out will be incremented by the same amount, so *next_out will now point at the amount of *avail_out unprocessed bytes.

The returned status indicates whether the encoder needs more output bytes. When the return value is not JXL_ENC_ERROR or JXL_ENC_SUCCESS, the encoding requires more JxlEncoderProcessOutput calls to continue.

The caller must guarantee that *avail_out >= 32 when calling JxlEncoderProcessOutput; otherwise, JXL_ENC_NEED_MORE_OUTPUT will be returned. It is guaranteed that, if *avail_out >= 32, at least one byte of output will be written.

This encodes the frames and/or boxes added so far. If the last frame or last box has been added, JxlEncoderCloseInput, JxlEncoderCloseFrames and/or JxlEncoderCloseBoxes must be called before the next JxlEncoderProcessOutput call, or the codestream won't be encoded correctly.

Parameters

  enc | encoder object.
  next_out | pointer to next bytes to write to.
  avail_out | amount of bytes available starting from *next_out.

Returns
  JXL_ENC_SUCCESS when encoding finished and all events handled.
  JXL_ENC_ERROR when encoding failed, e.g. invalid input.
  JXL_ENC_NEED_MORE_OUTPUT more output buffer is necessary.

## ◆ JxlEncoderReset()

JXL_EXPORT void JxlEncoderReset | ( | JxlEncoder * | enc | ) |

Re-initializes a JxlEncoder instance, so it can be re-used for encoding another image. All state and settings are reset as if the object was newly created with JxlEncoderCreate, but the memory manager is kept.

Parameters

  enc | instance to be re-initialized.

## ◆ JxlEncoderSetBasicInfo()

JXL_EXPORT JxlEncoderStatus JxlEncoderSetBasicInfo | ( | JxlEncoder * | enc,
|  | const JxlBasicInfo * | info )

Sets the global metadata of the image encoded by this encoder.

If the JxlBasicInfo contains information of extra channels beyond an alpha channel, then JxlEncoderSetExtraChannelInfo must be called between JxlEncoderSetBasicInfo and JxlEncoderAddImageFrame. In order to indicate extra channels, the value of `info.num_extra_channels` should be set to the number of extra channels, also counting the alpha channel if present.

Parameters

  enc | encoder object.
  info | global image metadata. Object owned by the caller and its contents are copied internally.

Returns
  JXL_ENC_SUCCESS if the operation was successful, JXL_ENC_ERROR otherwise

## ◆ JxlEncoderSetCms()

JXL_EXPORT void JxlEncoderSetCms | ( | JxlEncoder * | enc,
|  | JxlCmsInterface | cms )

Sets the color management system (CMS) that will be used for color conversion (if applicable) during encoding. May only be set before starting encoding. If left unset, the default CMS implementation will be used.

Parameters

  enc | encoder object.
  cms | structure representing a CMS implementation. See JxlCmsInterface for more details.

## ◆ JxlEncoderSetCodestreamLevel()

JXL_EXPORT JxlEncoderStatus JxlEncoderSetCodestreamLevel | ( | JxlEncoder * | enc,
|  | int | level )

Sets the feature level of the JPEG XL codestream. Valid values are 5 and 10, or -1 (to choose automatically). Using the minimum required level, or level 5 in most cases, is recommended for compatibility with all decoders.

Level 5: for end-user image delivery, this level is the most widely supported level by image decoders and the recommended level to use unless a level 10 feature is absolutely necessary. Supports a maximum resolution 268435456 pixels total with a maximum width or height of 262144 pixels, maximum 16-bit color channel depth, maximum 120 frames per second for animation, maximum ICC color profile size of 4 MiB, it allows all color models and extra channel types except CMYK and the JXL_CHANNEL_BLACK extra channel, and a maximum of 4 extra channels in addition to the 3 color channels. It also sets boundaries to certain internally used coding tools.

Level 10: this level removes or increases the bounds of most of the level 5 limitations, allows CMYK color and up to 32 bits per color channel, but may be less widely supported.

The default value is -1. This means the encoder will automatically choose between level 5 and level 10 based on what information is inside the JxlBasicInfo structure. Do note that some level 10 features, particularly those used by animated JPEG XL codestreams, might require level 10, even though the JxlBasicInfo only suggests level 5. In this case, the level must be explicitly set to 10, otherwise the encoder will return an error. The encoder will restrict internal encoding choices to those compatible with the level setting.

This setting can only be set at the beginning, before encoding starts.

Parameters

  enc | encoder object.
  level | the level value to set, must be -1, 5, or 10.

Returns
  JXL_ENC_SUCCESS if the operation was successful, JXL_ENC_ERROR otherwise.

## ◆ JxlEncoderSetColorEncoding()

JXL_EXPORT JxlEncoderStatus JxlEncoderSetColorEncoding | ( | JxlEncoder * | enc,
|  | const JxlColorEncoding * | color )

Sets the original color encoding of the image encoded by this encoder. This is an alternative to JxlEncoderSetICCProfile and only one of these two must be used. This one sets the color encoding as a JxlColorEncoding, while the other sets it as ICC binary data. Must be called after JxlEncoderSetBasicInfo.

Parameters

  enc | encoder object.
  color | color encoding. Object owned by the caller and its contents are copied internally.

Returns
  JXL_ENC_SUCCESS if the operation was successful, JXL_ENC_ERROR otherwise

## ◆ JxlEncoderSetDebugImageCallback()

JXL_EXPORT void JxlEncoderSetDebugImageCallback | ( | JxlEncoderFrameSettings * | frame_settings,
|  | JxlDebugImageCallback | callback,
|  | void * | opaque )

Sets the given debug image callback that will be used by the encoder to output various debug images during encoding.

This only has any effect if the encoder was compiled with the appropriate debug build flags.

Parameters

  frame_settings | set of options and metadata for this frame. Also includes reference to the encoder object.
  callback | used to return the debug image
  opaque | user supplied parameter to the image callback

## ◆ JxlEncoderSetExtraChannelBlendInfo()

JXL_EXPORT JxlEncoderStatus JxlEncoderSetExtraChannelBlendInfo | ( | JxlEncoderFrameSettings * | frame_settings,
|  | size_t | index,
|  | const JxlBlendInfo * | blend_info )

Sets blend info of an extra channel. The blend info of extra channels is set separately from that of the color channels, the color channels are set with JxlEncoderSetFrameHeader.

Parameters

  frame_settings | set of options and metadata for this frame. Also includes reference to the encoder object.
  index | index of the extra channel to use.
  blend_info | blend info to set for the extra channel

Returns
  JXL_ENC_SUCCESS on success, JXL_ENC_ERROR on error

## ◆ JxlEncoderSetExtraChannelBuffer()

JXL_EXPORT JxlEncoderStatus JxlEncoderSetExtraChannelBuffer | ( | const JxlEncoderFrameSettings * | frame_settings,
|  | const JxlPixelFormat * | pixel_format,
|  | const void * | buffer,
|  | size_t | size,
|  | uint32_t | index )

Sets the buffer to read pixels from for an extra channel at a given index. The index must be smaller than the num_extra_channels in the associated JxlBasicInfo. Must call JxlEncoderSetExtraChannelInfo before JxlEncoderSetExtraChannelBuffer.

TODO(firsching): mention what data types in pixel formats are supported.

It is required to call this function for every extra channel, except for the alpha channel if that was already set through JxlEncoderAddImageFrame.

Parameters

  frame_settings | set of options and metadata for this frame. Also includes reference to the encoder object.
  pixel_format | format for pixels. Object owned by the caller and its contents are copied internally. The num_channels value is ignored, since the number of channels for an extra channel is always assumed to be one.
  buffer | buffer type to input the pixel data from. Owned by the caller and its contents are copied internally.
  size | size of buffer in bytes. This size should match what is implied by the frame dimensions and the pixel format.
  index | index of the extra channel to use.

Returns
  JXL_ENC_SUCCESS on success, JXL_ENC_ERROR on error

## ◆ JxlEncoderSetExtraChannelDistance()

JXL_EXPORT JxlEncoderStatus JxlEncoderSetExtraChannelDistance | ( | JxlEncoderFrameSettings * | frame_settings,
|  | size_t | index,
|  | float | distance )

Sets the distance level for lossy compression of extra channels. The distance is as in JxlEncoderSetFrameDistance (lower = higher quality). If not set, or if set to the special value -1, the distance that was set with JxlEncoderSetFrameDistance will be used.

Parameters

  frame_settings | set of options and metadata for this frame. Also includes reference to the encoder object.
  index | index of the extra channel to set a distance value for.
  distance | the distance value to set.

Returns
  JXL_ENC_SUCCESS if the operation was successful, JXL_ENC_ERROR otherwise.

## ◆ JxlEncoderSetExtraChannelInfo()

JXL_EXPORT JxlEncoderStatus JxlEncoderSetExtraChannelInfo | ( | JxlEncoder * | enc,
|  | size_t | index,
|  | const JxlExtraChannelInfo * | info )

Sets information for the extra channel at the given index. The index must be smaller than num_extra_channels in the associated JxlBasicInfo.

Parameters

  enc | encoder object
  index | index of the extra channel to set.
  info | global extra channel metadata. Object owned by the caller and its contents are copied internally.

Returns
  JXL_ENC_SUCCESS on success, JXL_ENC_ERROR on error

## ◆ JxlEncoderSetExtraChannelName()

JXL_EXPORT JxlEncoderStatus JxlEncoderSetExtraChannelName | ( | JxlEncoder * | enc,
|  | size_t | index,
|  | const char * | name,
|  | size_t | size )

Sets the name for the extra channel at the given index in UTF-8. The index must be smaller than the num_extra_channels in the associated JxlBasicInfo.

TODO(lode): remove size parameter for consistency with JxlEncoderSetFrameName

Parameters

  enc | encoder object
  index | index of the extra channel to set.
  name | buffer with the name of the extra channel.
  size | size of the name buffer in bytes, not counting the terminating character.

Returns
  JXL_ENC_SUCCESS on success, JXL_ENC_ERROR on error

## ◆ JxlEncoderSetFrameBitDepth()

JXL_EXPORT JxlEncoderStatus JxlEncoderSetFrameBitDepth | ( | JxlEncoderFrameSettings * | frame_settings,
|  | const JxlBitDepth * | bit_depth )

Sets the bit depth of the input buffer.

For float pixel formats, only the default JXL_BIT_DEPTH_FROM_PIXEL_FORMAT setting is allowed, while for unsigned pixel formats, JXL_BIT_DEPTH_FROM_CODESTREAM setting is also allowed. See the comment on JxlEncoderAddImageFrame for the effects of the bit depth setting.

Parameters

  frame_settings | set of options and metadata for this frame. Also includes reference to the encoder object.
  bit_depth | the bit depth setting of the pixel input

Returns
  JXL_ENC_SUCCESS on success, JXL_ENC_ERROR on error

## ◆ JxlEncoderSetFrameDistance()

JXL_EXPORT JxlEncoderStatus JxlEncoderSetFrameDistance | ( | JxlEncoderFrameSettings * | frame_settings,
|  | float | distance )

Sets the distance level for lossy compression: target max butteraugli distance, lower = higher quality. Range: 0 .. 25. 0.0 = mathematically lossless (however, use JxlEncoderSetFrameLossless instead to use true lossless, as setting distance to 0 alone is not the only requirement). 1.0 = visually lossless. Recommended range: 0.5 .. 3.0. Default value: 1.0.

Parameters

  frame_settings | set of options and metadata for this frame. Also includes reference to the encoder object.
  distance | the distance value to set.

Returns
  JXL_ENC_SUCCESS if the operation was successful, JXL_ENC_ERROR otherwise.

## ◆ JxlEncoderSetFrameHeader()

JXL_EXPORT JxlEncoderStatus JxlEncoderSetFrameHeader | ( | JxlEncoderFrameSettings * | frame_settings,
|  | const JxlFrameHeader * | frame_header )

Sets the frame information for this frame to the encoder. This includes animation information such as frame duration to store in the frame header. The frame header fields represent the frame as passed to the encoder, but not necessarily the exact values as they will be encoded file format: the encoder could change crop and blending options of a frame for more efficient encoding or introduce additional internal frames. Animation duration and time code information is not altered since those are immutable metadata of the frame.

It is not required to use this function, however if have_animation is set to true in the basic info, then this function should be used to set the time duration of this individual frame. By default individual frames have a time duration of 0, making them form a composite still. See JxlFrameHeader for more information.

This information is stored in the JxlEncoderFrameSettings and so is used for any frame encoded with these JxlEncoderFrameSettings. It is ok to change between JxlEncoderAddImageFrame calls, each added image frame will have the frame header that was set in the options at the time of calling JxlEncoderAddImageFrame.

The is_last and name_length fields of the JxlFrameHeader are ignored, use JxlEncoderCloseFrames to indicate last frame, and JxlEncoderSetFrameName to indicate the name and its length instead. Calling this function will clear any name that was previously set with JxlEncoderSetFrameName.

Parameters

  frame_settings | set of options and metadata for this frame. Also includes reference to the encoder object.
  frame_header | frame header data to set. Object owned by the caller and does not need to be kept in memory, its information is copied internally.

Returns
  JXL_ENC_SUCCESS on success, JXL_ENC_ERROR on error

## ◆ JxlEncoderSetFrameLossless()

JXL_EXPORT JxlEncoderStatus JxlEncoderSetFrameLossless | ( | JxlEncoderFrameSettings * | frame_settings,
|  | JXL_BOOL | lossless )

Enables lossless encoding.

This is not an option like the others on itself, but rather while enabled it overrides a set of existing options (such as distance, modular mode and color transform) that enables bit-for-bit lossless encoding.

When disabled, those options are not overridden, but since those options could still have been manually set to a combination that operates losslessly, using this function with lossless set to JXL_FALSE does not guarantee lossy encoding, though the default set of options is lossy.

Parameters

  frame_settings | set of options and metadata for this frame. Also includes reference to the encoder object.
  lossless | whether to override options for lossless mode

Returns
  JXL_ENC_SUCCESS if the operation was successful, JXL_ENC_ERROR otherwise.

## ◆ JxlEncoderSetFrameName()

JXL_EXPORT JxlEncoderStatus JxlEncoderSetFrameName | ( | JxlEncoderFrameSettings * | frame_settings,
|  | const char * | frame_name )

Sets the name of the animation frame. This function is optional, frames are not required to have a name. This setting is a part of the frame header, and the same principles as for JxlEncoderSetFrameHeader apply. The name_length field of JxlFrameHeader is ignored by the encoder, this function determines the name length instead as the length in bytes of the C string.

The maximum possible name length is 1071 bytes (excluding terminating null character).

Calling JxlEncoderSetFrameHeader clears any name that was previously set.

Parameters

  frame_settings | set of options and metadata for this frame. Also includes reference to the encoder object.
  frame_name | name of the next frame to be encoded, as a UTF-8 encoded C string (zero terminated). Owned by the caller, and copied internally.

Returns
  JXL_ENC_SUCCESS on success, JXL_ENC_ERROR on error

## ◆ JxlEncoderSetICCProfile()

JXL_EXPORT JxlEncoderStatus JxlEncoderSetICCProfile | ( | JxlEncoder * | enc,
|  | const uint8_t * | icc_profile,
|  | size_t | size )

Sets the original color encoding of the image encoded by this encoder as an ICC color profile. This is an alternative to JxlEncoderSetColorEncoding and only one of these two must be used. This one sets the color encoding as ICC binary data, while the other defines it as a JxlColorEncoding. Must be called after JxlEncoderSetBasicInfo.

Parameters

  enc | encoder object.
  icc_profile | bytes of the original ICC profile
  size | size of the icc_profile buffer in bytes

Returns
  JXL_ENC_SUCCESS if the operation was successful, JXL_ENC_ERROR otherwise

## ◆ JxlEncoderSetOutputProcessor()

JXL_EXPORT JxlEncoderStatus JxlEncoderSetOutputProcessor | ( | JxlEncoder * | enc,
|  | struct JxlEncoderOutputProcessor | output_processor )

Sets the output processor for the encoder. This processor determines how the encoder will handle buffering, writing, seeking (if supported), and setting a finalized position during the encoding process.

This should not be used when using JxlEncoderProcessOutput.

Parameters

  enc | encoder object.
  output_processor | the struct containing the callbacks for managing output.

Returns
  JXL_ENC_SUCCESS on success, JXL_ENC_ERROR on error.

## ◆ JxlEncoderSetParallelRunner()

JXL_EXPORT JxlEncoderStatus JxlEncoderSetParallelRunner | ( | JxlEncoder * | enc,
|  | JxlParallelRunner | parallel_runner,
|  | void * | parallel_runner_opaque )

Set the parallel runner for multithreading. May only be set before starting encoding.

Parameters

  enc | encoder object.
  parallel_runner | function pointer to runner for multithreading. It may be NULL to use the default, single-threaded, runner. A multithreaded runner should be set to reach fast performance.
  parallel_runner_opaque | opaque pointer for parallel_runner.

Returns
  JXL_ENC_SUCCESS if the runner was set, JXL_ENC_ERROR otherwise (the previous runner remains set).

## ◆ JxlEncoderSetUpsamplingMode()

JXL_EXPORT JxlEncoderStatus JxlEncoderSetUpsamplingMode | ( | JxlEncoder * | enc,
|  | int64_t | factor,
|  | int64_t | mode )

Sets the upsampling method the decoder will use in case there are frames with JXL_ENC_FRAME_SETTING_RESAMPLING set. This is useful in combination with the JXL_ENC_FRAME_SETTING_ALREADY_DOWNSAMPLED option, to control the type of upsampling that will be used.

Parameters

  enc | encoder object.
  factor | upsampling factor to configure (1, 2, 4 or 8; for 1 this function has no effect at all)
  mode | upsampling mode to use for this upsampling: -1: default (good for photographic images, no signaling overhead) 0: nearest neighbor (good for pixel art) 1: 'pixel dots' (same as NN for 2x, diamond-shaped 'pixel dots' for 4x/8x)

Returns
  JXL_ENC_SUCCESS if the operation was successful, JXL_ENC_ERROR otherwise

## ◆ JxlEncoderStatsCreate()

JXL_EXPORT JxlEncoderStats * JxlEncoderStatsCreate | ( | void |  | ) |

Creates an instance of JxlEncoderStats and initializes it.

Returns
  pointer to initialized JxlEncoderStats instance

## ◆ JxlEncoderStatsDestroy()

JXL_EXPORT void JxlEncoderStatsDestroy | ( | JxlEncoderStats * | stats | ) |

Deinitializes and frees JxlEncoderStats instance.

Parameters

  stats | instance to be cleaned up and deallocated. No-op if stats is null pointer.

## ◆ JxlEncoderStatsGet()

JXL_EXPORT size_t JxlEncoderStatsGet | ( | const JxlEncoderStats * | stats,
|  | JxlEncoderStatsKey | key )

Returns the value of the statistics corresponding the given key.

Parameters

  stats | object that was passed to the encoder with a JxlEncoderCollectStats function
  key | the particular statistics to query

Returns
  the value of the statistics

## ◆ JxlEncoderStatsMerge()

JXL_EXPORT void JxlEncoderStatsMerge | ( | JxlEncoderStats * | stats,
|  | const JxlEncoderStats * | other )

Updates the values of the given stats object with that of an other.

Parameters

  stats | object whose values will be updated (usually added together)
  other | stats object whose values will be merged with stats

## ◆ JxlEncoderStoreJPEGMetadata()

JXL_EXPORT JxlEncoderStatus JxlEncoderStoreJPEGMetadata | ( | JxlEncoder * | enc,
|  | JXL_BOOL | store_jpeg_metadata )

Configure the encoder to store JPEG reconstruction metadata in the JPEG XL container.

If this is set to true and a single JPEG frame is added, it will be possible to losslessly reconstruct the JPEG codestream.

This setting can only be set at the beginning, before encoding starts.

Parameters

  enc | encoder object.
  store_jpeg_metadata | true if the encoder should store JPEG metadata.

Returns
  JXL_ENC_SUCCESS if the operation was successful, JXL_ENC_ERROR otherwise.

## ◆ JxlEncoderUseBoxes()

JXL_EXPORT JxlEncoderStatus JxlEncoderUseBoxes | ( | JxlEncoder * | enc | ) |

Indicates the intention to add metadata boxes. This allows JxlEncoderAddBox to be used. When using this function, then it is required to use JxlEncoderCloseBoxes at the end.

By default the encoder assumes no metadata boxes will be added.

This setting can only be set at the beginning, before encoding starts.

Parameters

  enc | encoder object.

## ◆ JxlEncoderUseContainer()

JXL_EXPORT JxlEncoderStatus JxlEncoderUseContainer | ( | JxlEncoder * | enc,
|  | JXL_BOOL | use_container )

Forces the encoder to use the box-based container format (BMFF) even when not necessary.

When using JxlEncoderUseBoxes, JxlEncoderStoreJPEGMetadata or JxlEncoderSetCodestreamLevel with level 10, the encoder will automatically also use the container format, it is not necessary to use JxlEncoderUseContainer for those use cases.

By default this setting is disabled.

This setting can only be set at the beginning, before encoding starts.

Parameters

  enc | encoder object.
  use_container | true if the encoder should always output the JPEG XL container format, false to only output it when necessary.

Returns
  JXL_ENC_SUCCESS if the operation was successful, JXL_ENC_ERROR otherwise.

## ◆ JxlEncoderVersion()

JXL_EXPORT uint32_t JxlEncoderVersion | ( | void |  | ) |

Encoder library version.

Returns
  the encoder library version as an integer: MAJOR_VERSION * 1000000 + MINOR_VERSION * 1000 + PATCH_VERSION. For example, version 1.2.3 would return 1002003.