/* * 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 { … }; #endif
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