/* | |

* 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" | |

/** | |

* 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). | |

*/ | |

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 { | |

kSDR, | |

kHDR, | |

}; | |

BaseImageType fBaseImageType = BaseImageType::kSDR; | |

// TODO(ccameron): Remove these parameters after the new parameters roll into Android. | |

SkColor4f fLogRatioMin = {0.f, 0.f, 0.f, 1.0}; | |

SkColor4f fLogRatioMax = {1.f, 1.f, 1.f, 1.0}; | |

float fHdrRatioMin = 1.f; | |

float fHdrRatioMax = 50.f; | |

/** | |

* The type of file that created this gainmap. | |

*/ | |

enum class Type { | |

kUnknown, | |

kMultiPicture, | |

kJpegR_Linear, | |

kJpegR_HLG, | |

kJpegR_PQ, | |

kHDRGM, | |

}; | |

Type fType = Type::kUnknown; | |

}; | |

#endif |