| /* |
| * Copyright 2016 Google Inc. |
| * |
| * Use of this source code is governed by a BSD-style license that can be |
| * found in the LICENSE file. |
| */ |
| |
| #ifndef SkSRGB_DEFINED |
| #define SkSRGB_DEFINED |
| |
| #include "SkNx.h" |
| |
| /** Components for building our canonical sRGB -> linear and linear -> sRGB transformations. |
| * |
| * Current best practices: |
| * - for sRGB -> linear, lookup R,G,B in sk_linear_from_srgb; |
| * - for linear -> sRGB, call sk_linear_to_srgb() for R,G,B, and round; |
| * - the alpha channel is linear in both formats, needing at most *(1/255.0f) or *255.0f. |
| * |
| * sk_linear_to_srgb()'s output requires rounding; it does not round for you. |
| * |
| * Given inputs in [0,1], sk_linear_to_srgb() will not underflow 0 but may overflow 255. |
| * The overflow is small enough to be handled by rounding. |
| * (But if you don't trust the inputs are in [0,1], you'd better clamp both sides immediately.) |
| * |
| * sk_linear_to_srgb() will run a little faster than usual when compiled with SSE4.1+. |
| */ |
| |
| extern const float sk_linear_from_srgb[256]; |
| |
| static inline Sk4f sk_linear_to_srgb(const Sk4f& x) { |
| // Approximation of the sRGB gamma curve (within 1 when scaled to 8-bit pixels). |
| // For 0.00000f <= x < 0.00349f, 12.92 * x |
| // For 0.00349f <= x <= 1.00000f, 0.679*(x.^0.5) + 0.423*x.^(0.25) - 0.101 |
| // Note that 0.00349 was selected because it is a point where both functions produce the |
| // same pixel value when rounded. |
| auto rsqrt = x.rsqrt(), |
| sqrt = rsqrt.invert(), |
| ftrt = rsqrt.rsqrt(); |
| |
| auto lo = (12.92f * 255.0f) * x; |
| |
| auto hi = (-0.101115084998961f * 255.0f) + |
| (+0.678513029959381f * 255.0f) * sqrt + |
| (+0.422602055039580f * 255.0f) * ftrt; |
| |
| return (x < 0.00349f).thenElse(lo, hi); |
| } |
| |
| #endif//SkSRGB_DEFINED |