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* Copyright 2018 Google Inc.
* Use of this source code is governed by a BSD-style license that can be
* found in the LICENSE file.
#pragma once
// skcms.h contains the entire public API for skcms.
#ifndef SKCMS_API
#define SKCMS_API
#include <stdbool.h>
#include <stddef.h>
#include <stdint.h>
#include <string.h>
#ifdef __cplusplus
extern "C" {
// A row-major 3x3 matrix (ie vals[row][col])
typedef struct skcms_Matrix3x3 {
float vals[3][3];
} skcms_Matrix3x3;
// It is _not_ safe to alias the pointers to invert in-place.
SKCMS_API bool skcms_Matrix3x3_invert(const skcms_Matrix3x3*, skcms_Matrix3x3*);
SKCMS_API skcms_Matrix3x3 skcms_Matrix3x3_concat(const skcms_Matrix3x3*, const skcms_Matrix3x3*);
// A row-major 3x4 matrix (ie vals[row][col])
typedef struct skcms_Matrix3x4 {
float vals[3][4];
} skcms_Matrix3x4;
// A transfer function mapping encoded values to linear values,
// represented by this 7-parameter piecewise function:
// linear = sign(encoded) * (c*|encoded| + f) , 0 <= |encoded| < d
// = sign(encoded) * ((a*|encoded| + b)^g + e), d <= |encoded|
// (A simple gamma transfer function sets g to gamma and a to 1.)
typedef struct skcms_TransferFunction {
float g, a,b,c,d,e,f;
} skcms_TransferFunction;
SKCMS_API float skcms_TransferFunction_eval (const skcms_TransferFunction*, float);
SKCMS_API bool skcms_TransferFunction_invert(const skcms_TransferFunction*,
// We can jam a couple alternate transfer function forms into skcms_TransferFunction,
// including those matching the general forms of the SMPTE ST 2084 PQ function or HLG.
// PQish:
// max(A + B|encoded|^C, 0)
// linear = sign(encoded) * (------------------------) ^ F
// D + E|encoded|^C
SKCMS_API bool skcms_TransferFunction_makePQish(skcms_TransferFunction*,
float A, float B, float C,
float D, float E, float F);
// HLGish:
// { K * sign(encoded) * ( (R|encoded|)^G ) when 0 <= |encoded| <= 1/R
// linear = { K * sign(encoded) * ( e^(a(|encoded|-c)) + b ) when 1/R < |encoded|
SKCMS_API bool skcms_TransferFunction_makeScaledHLGish(skcms_TransferFunction*,
float K, float R, float G,
float a, float b, float c);
// Compatibility shim with K=1 for old callers.
static inline bool skcms_TransferFunction_makeHLGish(skcms_TransferFunction* fn,
float R, float G,
float a, float b, float c) {
return skcms_TransferFunction_makeScaledHLGish(fn, 1.0f, R,G, a,b,c);
// PQ mapping encoded [0,1] to linear [0,1].
static inline bool skcms_TransferFunction_makePQ(skcms_TransferFunction* tf) {
return skcms_TransferFunction_makePQish(tf, -107/128.0f, 1.0f, 32/2523.0f
, 2413/128.0f, -2392/128.0f, 8192/1305.0f);
// HLG mapping encoded [0,1] to linear [0,12].
static inline bool skcms_TransferFunction_makeHLG(skcms_TransferFunction* tf) {
return skcms_TransferFunction_makeHLGish(tf, 2.0f, 2.0f
, 1/0.17883277f, 0.28466892f, 0.55991073f);
// Is this an ordinary sRGB-ish transfer function, or one of the HDR forms we support?
SKCMS_API bool skcms_TransferFunction_isSRGBish(const skcms_TransferFunction*);
SKCMS_API bool skcms_TransferFunction_isPQish (const skcms_TransferFunction*);
SKCMS_API bool skcms_TransferFunction_isHLGish (const skcms_TransferFunction*);
// Unified representation of 'curv' or 'para' tag data, or a 1D table from 'mft1' or 'mft2'
typedef union skcms_Curve {
struct {
uint32_t alias_of_table_entries;
skcms_TransferFunction parametric;
struct {
uint32_t table_entries;
const uint8_t* table_8;
const uint8_t* table_16;
} skcms_Curve;
typedef struct skcms_A2B {
// Optional: N 1D curves, followed by an N-dimensional CLUT.
// If input_channels == 0, these curves and CLUT are skipped,
// Otherwise, input_channels must be in [1, 4].
uint32_t input_channels;
skcms_Curve input_curves[4];
uint8_t grid_points[4];
const uint8_t* grid_8;
const uint8_t* grid_16;
// Optional: 3 1D curves, followed by a color matrix.
// If matrix_channels == 0, these curves and matrix are skipped,
// Otherwise, matrix_channels must be 3.
uint32_t matrix_channels;
skcms_Curve matrix_curves[3];
skcms_Matrix3x4 matrix;
// Required: 3 1D curves. Always present, and output_channels must be 3.
uint32_t output_channels;
skcms_Curve output_curves[3];
} skcms_A2B;
typedef struct skcms_ICCProfile {
const uint8_t* buffer;
uint32_t size;
uint32_t data_color_space;
uint32_t pcs;
uint32_t tag_count;
// skcms_Parse() will set commonly-used fields for you when possible:
// If we can parse red, green and blue transfer curves from the profile,
// trc will be set to those three curves, and has_trc will be true.
bool has_trc;
skcms_Curve trc[3];
// If this profile's gamut can be represented by a 3x3 transform to XYZD50,
// skcms_Parse() sets toXYZD50 to that transform and has_toXYZD50 to true.
bool has_toXYZD50;
skcms_Matrix3x3 toXYZD50;
// If the profile has a valid A2B0 tag, skcms_Parse() sets A2B to that data,
// and has_A2B to true.
bool has_A2B;
skcms_A2B A2B;
} skcms_ICCProfile;
// The sRGB color profile is so commonly used that we offer a canonical skcms_ICCProfile for it.
SKCMS_API const skcms_ICCProfile* skcms_sRGB_profile(void);
// Ditto for XYZD50, the most common profile connection space.
SKCMS_API const skcms_ICCProfile* skcms_XYZD50_profile(void);
SKCMS_API const skcms_TransferFunction* skcms_sRGB_TransferFunction(void);
SKCMS_API const skcms_TransferFunction* skcms_sRGB_Inverse_TransferFunction(void);
SKCMS_API const skcms_TransferFunction* skcms_Identity_TransferFunction(void);
// Practical equality test for two skcms_ICCProfiles.
// The implementation is subject to change, but it will always try to answer
// "can I substitute A for B?" and "can I skip transforming from A to B?".
SKCMS_API bool skcms_ApproximatelyEqualProfiles(const skcms_ICCProfile* A,
const skcms_ICCProfile* B);
// Practical test that answers: Is curve roughly the inverse of inv_tf? Typically used by passing
// the inverse of a known parametric transfer function (like sRGB), to determine if a particular
// curve is very close to sRGB.
SKCMS_API bool skcms_AreApproximateInverses(const skcms_Curve* curve,
const skcms_TransferFunction* inv_tf);
// Similar to above, answering the question for all three TRC curves of the given profile. Again,
// passing skcms_sRGB_InverseTransferFunction as inv_tf will answer the question:
// "Does this profile have a transfer function that is very close to sRGB?"
SKCMS_API bool skcms_TRCs_AreApproximateInverse(const skcms_ICCProfile* profile,
const skcms_TransferFunction* inv_tf);
// Parse an ICC profile and return true if possible, otherwise return false.
// The buffer is not copied, it must remain valid as long as the skcms_ICCProfile
// will be used.
SKCMS_API bool skcms_Parse(const void*, size_t, skcms_ICCProfile*);
SKCMS_API bool skcms_ApproximateCurve(const skcms_Curve* curve,
skcms_TransferFunction* approx,
float* max_error);
SKCMS_API bool skcms_GetCHAD(const skcms_ICCProfile*, skcms_Matrix3x3*);
SKCMS_API bool skcms_GetWTPT(const skcms_ICCProfile*, float xyz[3]);
// These are common ICC signature values
enum {
// data_color_space
skcms_Signature_CMYK = 0x434D594B,
skcms_Signature_Gray = 0x47524159,
skcms_Signature_RGB = 0x52474220,
// pcs
skcms_Signature_Lab = 0x4C616220,
skcms_Signature_XYZ = 0x58595A20,
typedef enum skcms_PixelFormat {
skcms_PixelFormat_RGBA_8888_sRGB, // Automatic sRGB encoding / decoding.
skcms_PixelFormat_BGRA_8888_sRGB, // (Generally used with linear transfer functions.)
skcms_PixelFormat_RGB_161616LE, // Little-endian. Pointers must be 16-bit aligned.
skcms_PixelFormat_RGB_161616BE, // Big-endian. Pointers must be 16-bit aligned.
skcms_PixelFormat_RGB_hhh_Norm, // 1-5-10 half-precision float in [0,1]
skcms_PixelFormat_BGR_hhh_Norm, // Pointers must be 16-bit aligned.
skcms_PixelFormat_RGB_hhh, // 1-5-10 half-precision float.
skcms_PixelFormat_BGR_hhh, // Pointers must be 16-bit aligned.
skcms_PixelFormat_RGB_fff, // 1-8-23 single-precision float (the normal kind).
skcms_PixelFormat_BGR_fff, // Pointers must be 32-bit aligned.
} skcms_PixelFormat;
// We always store any alpha channel linearly. In the chart below, tf-1() is the inverse
// transfer function for the given color profile (applying the transfer function linearizes).
// We treat opaque as a strong requirement, not just a performance hint: we will ignore
// any source alpha and treat it as 1.0, and will make sure that any destination alpha
// channel is filled with the equivalent of 1.0.
// We used to offer multiple types of premultiplication, but now just one, PremulAsEncoded.
// This is the premul you're probably used to working with.
typedef enum skcms_AlphaFormat {
skcms_AlphaFormat_Opaque, // alpha is always opaque
// tf-1(r), tf-1(g), tf-1(b), 1.0
skcms_AlphaFormat_Unpremul, // alpha and color are unassociated
// tf-1(r), tf-1(g), tf-1(b), a
skcms_AlphaFormat_PremulAsEncoded, // premultiplied while encoded
// tf-1(r)*a, tf-1(g)*a, tf-1(b)*a, a
} skcms_AlphaFormat;
// Convert npixels pixels from src format and color profile to dst format and color profile
// and return true, otherwise return false. It is safe to alias dst == src if dstFmt == srcFmt.
SKCMS_API bool skcms_Transform(const void* src,
skcms_PixelFormat srcFmt,
skcms_AlphaFormat srcAlpha,
const skcms_ICCProfile* srcProfile,
void* dst,
skcms_PixelFormat dstFmt,
skcms_AlphaFormat dstAlpha,
const skcms_ICCProfile* dstProfile,
size_t npixels);
// As skcms_Transform(), supporting srcFmts with a palette.
SKCMS_API bool skcms_TransformWithPalette(const void* src,
skcms_PixelFormat srcFmt,
skcms_AlphaFormat srcAlpha,
const skcms_ICCProfile* srcProfile,
void* dst,
skcms_PixelFormat dstFmt,
skcms_AlphaFormat dstAlpha,
const skcms_ICCProfile* dstProfile,
size_t npixels,
const void* palette);
// If profile can be used as a destination in skcms_Transform, return true. Otherwise, attempt to
// rewrite it with approximations where reasonable. If successful, return true. If no reasonable
// approximation exists, leave the profile unchanged and return false.
SKCMS_API bool skcms_MakeUsableAsDestination(skcms_ICCProfile* profile);
// If profile can be used as a destination with a single parametric transfer function (ie for
// rasterization), return true. Otherwise, attempt to rewrite it with approximations where
// reasonable. If successful, return true. If no reasonable approximation exists, leave the
// profile unchanged and return false.
SKCMS_API bool skcms_MakeUsableAsDestinationWithSingleCurve(skcms_ICCProfile* profile);
// Returns a matrix to adapt XYZ color from given the whitepoint to D50.
SKCMS_API bool skcms_AdaptToXYZD50(float wx, float wy,
skcms_Matrix3x3* toXYZD50);
// Returns a matrix to convert RGB color into XYZ adapted to D50, given the
// primaries and whitepoint of the RGB model.
SKCMS_API bool skcms_PrimariesToXYZD50(float rx, float ry,
float gx, float gy,
float bx, float by,
float wx, float wy,
skcms_Matrix3x3* toXYZD50);
// Call before your first call to skcms_Transform() to skip runtime CPU detection.
SKCMS_API void skcms_DisableRuntimeCPUDetection(void);
// Utilities for programmatically constructing profiles
static inline void skcms_Init(skcms_ICCProfile* p) {
memset(p, 0, sizeof(*p));
p->data_color_space = skcms_Signature_RGB;
p->pcs = skcms_Signature_XYZ;
static inline void skcms_SetTransferFunction(skcms_ICCProfile* p,
const skcms_TransferFunction* tf) {
p->has_trc = true;
for (int i = 0; i < 3; ++i) {
p->trc[i].table_entries = 0;
p->trc[i].parametric = *tf;
static inline void skcms_SetXYZD50(skcms_ICCProfile* p, const skcms_Matrix3x3* m) {
p->has_toXYZD50 = true;
p->toXYZD50 = *m;
#ifdef __cplusplus