/* * 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_public.h contains the entire public API for skcms. #ifndef SKCMS_API #define SKCMS_API #endif #include <stdbool.h> #include <stddef.h> #include <stdint.h> #include <string.h> #ifdef __cplusplus extern "C" { #endif // A row-major 3x3 matrix (ie vals[row][col]) 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]) 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.) skcms_TransferFunction; SKCMS_API float skcms_TransferFunction_eval (const skcms_TransferFunction*, float); SKCMS_API bool skcms_TransferFunction_invert(const skcms_TransferFunction*, skcms_TransferFunction*); skcms_TFType; // Identify which kind of transfer function is encoded in an skcms_TransferFunction SKCMS_API skcms_TFType skcms_TransferFunction_getType(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) { … } // PQ mapping encoded [0,1] to linear [0,1]. static inline bool skcms_TransferFunction_makePQ(skcms_TransferFunction* tf) { … } // HLG mapping encoded [0,1] to linear [0,12]. static inline bool skcms_TransferFunction_makeHLG(skcms_TransferFunction* tf) { … } // 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' skcms_Curve; // Complex transforms between device space (A) and profile connection space (B): // A2B: device -> [ "A" curves -> CLUT ] -> [ "M" curves -> matrix ] -> "B" curves -> PCS // B2A: device <- [ "A" curves <- CLUT ] <- [ "M" curves <- matrix ] <- "B" curves <- PCS skcms_A2B; skcms_B2A; skcms_CICP; 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. // Selects an A2B profile (if present) according to priority list (each entry 0-2). // The buffer is not copied; it must remain valid as long as the skcms_ICCProfile will be used. SKCMS_API bool skcms_ParseWithA2BPriority(const void*, size_t, const int priority[], int priorities, skcms_ICCProfile*); static inline bool skcms_Parse(const void* buf, size_t len, skcms_ICCProfile* profile) { … } 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]); // Returns the number of channels of input data that are expected on the "A" side of the profile. // This is useful for image codecs, where the image data and the accompanying profile might have // conflicting data shapes. In some cases, the result is unclear or invalid. In that case, the // function will return a negative value to signal an error. SKCMS_API int skcms_GetInputChannelCount(const skcms_ICCProfile*); // These are common ICC signature values enum { … }; 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. 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); // 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) { … } static inline void skcms_SetTransferFunction(skcms_ICCProfile* p, const skcms_TransferFunction* tf) { … } static inline void skcms_SetXYZD50(skcms_ICCProfile* p, const skcms_Matrix3x3* m) { … } #ifdef __cplusplus } #endif
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