blob: 07512a4510623faca9bc7b760483510b85545599 [file] [log] [blame]
* Copyright 2023 Google Inc.
* Use of this source code is governed by a BSD-style license that can be
* found in the LICENSE file.
#ifndef SkGainmapInfo_DEFINED
#define SkGainmapInfo_DEFINED
#include "include/core/SkColor.h"
#include "include/core/SkColorSpace.h"
#include "include/core/SkRefCnt.h"
class SkData;
* Gainmap rendering parameters. Suppose our display has HDR to SDR ratio of H and we wish to
* display an image with gainmap on this display. Let B be the pixel value from the base image
* in a color space that has the primaries of the base image and a linear transfer function. Let
* G be the pixel value from the gainmap. Let D be the output pixel in the same color space as B.
* The value of D is computed as follows:
* First, let W be a weight parameter determing how much the gainmap will be applied.
* W = clamp((log(H) - log(fDisplayRatioSdr)) /
* (log(fDisplayRatioHdr) - log(fDisplayRatioSdr), 0, 1)
* Next, let L be the gainmap value in log space. We compute this from the value G that was
* sampled from the texture as follows:
* L = mix(log(fGainmapRatioMin), log(fGainmapRatioMax), pow(G, fGainmapGamma))
* Finally, apply the gainmap to compute D, the displayed pixel. If the base image is SDR then
* compute:
* D = (B + fEpsilonSdr) * exp(L * W) - fEpsilonHdr
* If the base image is HDR then compute:
* D = (B + fEpsilonHdr) * exp(L * (W - 1)) - fEpsilonSdr
* In the above math, log() is a natural logarithm and exp() is natural exponentiation. Note,
* however, that the base used for the log() and exp() functions does not affect the results of
* the computation (it cancels out, as long as the same base is used throughout).
* This product includes Gain Map technology under license by Adobe.
struct SkGainmapInfo {
* Parameters for converting the gainmap from its image encoding to log space. These are
* specified per color channel. The alpha value is unused.
SkColor4f fGainmapRatioMin = {1.f, 1.f, 1.f, 1.0};
SkColor4f fGainmapRatioMax = {2.f, 2.f, 2.f, 1.0};
SkColor4f fGainmapGamma = {1.f, 1.f, 1.f, 1.f};
* Parameters sometimes used in gainmap computation to avoid numerical instability.
SkColor4f fEpsilonSdr = {0.f, 0.f, 0.f, 1.0};
SkColor4f fEpsilonHdr = {0.f, 0.f, 0.f, 1.0};
* If the output display's HDR to SDR ratio is less or equal than fDisplayRatioSdr then the SDR
* rendition is displayed. If the output display's HDR to SDR ratio is greater or equal than
* fDisplayRatioHdr then the HDR rendition is displayed. If the output display's HDR to SDR
* ratio is between these values then an interpolation between the two is displayed using the
* math above.
float fDisplayRatioSdr = 1.f;
float fDisplayRatioHdr = 2.f;
* Whether the base image is the SDR image or the HDR image.
enum class BaseImageType {
BaseImageType fBaseImageType = BaseImageType::kSDR;
* The type of the gainmap image. If the type is kApple, then the gainmap image was originally
* encoded according to the specification at [0], and can be converted to the kDefault type by
* applying the transformation described at [1].
* [0]
* applying_apple_hdr_effect_to_your_photos
* [1]
enum class Type {
Type fType = Type::kDefault;
* If specified, color space to apply the gainmap in, otherwise the base image's color space
* is used. Only the color primaries are used, the transfer function is irrelevant.
sk_sp<SkColorSpace> fGainmapMathColorSpace = nullptr;
* If |data| contains an ISO 21496-1 version that is supported, return true. Otherwise return
* false.
static bool ParseVersion(const SkData* data);
* If |data| constains ISO 21496-1 metadata then parse that metadata then use it to populate
* |info| and return true, otherwise return false. If |data| indicates that that the base image
* color space primaries should be used for gainmap application then set
* |fGainmapMathColorSpace| to nullptr, otherwise set |fGainmapMathColorSpace| to sRGB (the
* default, to be overwritten by the image decoder).
static bool Parse(const SkData* data, SkGainmapInfo& info);
* Serialize an ISO 21496-1 version 0 blob containing only the version structure.
static sk_sp<SkData> SerializeVersion();
* Serialize an ISO 21496-1 version 0 blob containing this' gainmap parameters.
sk_sp<SkData> serialize() const;
inline bool operator==(const SkGainmapInfo& other) const {
return fGainmapRatioMin == other.fGainmapRatioMin &&
fGainmapRatioMax == other.fGainmapRatioMax && fGainmapGamma == other.fGainmapGamma &&
fEpsilonSdr == other.fEpsilonSdr && fEpsilonHdr == other.fEpsilonHdr &&
fDisplayRatioSdr == other.fDisplayRatioSdr &&
fDisplayRatioHdr == other.fDisplayRatioHdr &&
fBaseImageType == other.fBaseImageType && fType == other.fType &&
inline bool operator!=(const SkGainmapInfo& other) const { return !(*this == other); }