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Improve documentation of SharpYuvConversionMatrix.

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Change-Id: I39898bf53db759b68c86c9005c11ded20de4eb3e
This commit is contained in:
Maryla 2024-10-03 10:35:58 +02:00
parent 169dfbf931
commit 0c3cd9cc2c
3 changed files with 23 additions and 9 deletions
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17
sharpyuv/sharpyuv.h
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@ -66,10 +66,17 @@ extern "C" {
SHARPYUV_EXTERN int SharpYuvGetVersion(void);
// RGB to YUV conversion matrix, in 16 bit fixed point.
// y = rgb_to_y[0] * r + rgb_to_y[1] * g + rgb_to_y[2] * b + rgb_to_y[3]
// u = rgb_to_u[0] * r + rgb_to_u[1] * g + rgb_to_u[2] * b + rgb_to_u[3]
// v = rgb_to_v[0] * r + rgb_to_v[1] * g + rgb_to_v[2] * b + rgb_to_v[3]
// Then y, u and v values are divided by 1<<16 and rounded.
// y_ = rgb_to_y[0] * r + rgb_to_y[1] * g + rgb_to_y[2] * b + rgb_to_y[3]
// u_ = rgb_to_u[0] * r + rgb_to_u[1] * g + rgb_to_u[2] * b + rgb_to_u[3]
// v_ = rgb_to_v[0] * r + rgb_to_v[1] * g + rgb_to_v[2] * b + rgb_to_v[3]
// Then the values are divided by 1<<16 and rounded.
// y = (y_ + (1 << 15)) >> 16
// u = (u_ + (1 << 15)) >> 16
// v = (v_ + (1 << 15)) >> 16
//
// Typically, the offset values rgb_to_y[3], rgb_to_u[3] and rgb_to_v[3] depend
// on the input's bit depth, e.g., rgb_to_u[3] = 1 << (rgb_bit_depth - 1 + 16).
// See also sharpyuv_csp.h to get a predefined matrix or generate a matrix.
typedef struct {
int rgb_to_y[4];
int rgb_to_u[4];
@ -127,6 +134,8 @@ typedef enum SharpYuvTransferFunctionType {
// adjacent pixels on the y, u and v channels. If yuv_bit_depth > 8, they
// should be multiples of 2.
// width, height: width and height of the image in pixels
// yuv_matrix: RGB to YUV conversion matrix. The matrix values typically
// depend on the input's rgb_bit_depth.
// This function calls SharpYuvConvertWithOptions with a default transfer
// function of kSharpYuvTransferFunctionSrgb.
SHARPYUV_EXTERN int SharpYuvConvert(const void* r_ptr, const void* g_ptr,

10
sharpyuv/sharpyuv_csp.c
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@ -59,31 +59,31 @@ void SharpYuvComputeConversionMatrix(const SharpYuvColorSpace* yuv_color_space,
}
// Matrices are in YUV_FIX fixed point precision.
// WebP's matrix, similar but not identical to kRec601LimitedMatrix.
// WebP's matrix, similar but not identical to kRec601LimitedMatrix
static const SharpYuvConversionMatrix kWebpMatrix = {
{16839, 33059, 6420, 16 << 16},
{-9719, -19081, 28800, 128 << 16},
{28800, -24116, -4684, 128 << 16},
};
// Kr=0.2990f Kb=0.1140f bits=8 range=kSharpYuvRangeLimited
// Kr=0.2990f Kb=0.1140f bit_depth=8 range=kSharpYuvRangeLimited
static const SharpYuvConversionMatrix kRec601LimitedMatrix = {
{16829, 33039, 6416, 16 << 16},
{-9714, -19071, 28784, 128 << 16},
{28784, -24103, -4681, 128 << 16},
};
// Kr=0.2990f Kb=0.1140f bits=8 range=kSharpYuvRangeFull
// Kr=0.2990f Kb=0.1140f bit_depth=8 range=kSharpYuvRangeFull
static const SharpYuvConversionMatrix kRec601FullMatrix = {
{19595, 38470, 7471, 0},
{-11058, -21710, 32768, 128 << 16},
{32768, -27439, -5329, 128 << 16},
};
// Kr=0.2126f Kb=0.0722f bits=8 range=kSharpYuvRangeLimited
// Kr=0.2126f Kb=0.0722f bit_depth=8 range=kSharpYuvRangeLimited
static const SharpYuvConversionMatrix kRec709LimitedMatrix = {
{11966, 40254, 4064, 16 << 16},
{-6596, -22189, 28784, 128 << 16},
{28784, -26145, -2639, 128 << 16},
};
// Kr=0.2126f Kb=0.0722f bits=8 range=kSharpYuvRangeFull
// Kr=0.2126f Kb=0.0722f bit_depth=8 range=kSharpYuvRangeFull
static const SharpYuvConversionMatrix kRec709FullMatrix = {
{13933, 46871, 4732, 0},
{-7509, -25259, 32768, 128 << 16},

5
sharpyuv/sharpyuv_csp.h
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@ -41,10 +41,15 @@ SHARPYUV_EXTERN void SharpYuvComputeConversionMatrix(
// Enums for precomputed conversion matrices.
typedef enum {
// WebP's matrix, similar but not identical to kSharpYuvMatrixRec601Limited
kSharpYuvMatrixWebp = 0,
// Kr=0.2990f Kb=0.1140f bit_depth=8 range=kSharpYuvRangeLimited
kSharpYuvMatrixRec601Limited,
// Kr=0.2990f Kb=0.1140f bit_depth=8 range=kSharpYuvRangeFull
kSharpYuvMatrixRec601Full,
// Kr=0.2126f Kb=0.0722f bit_depth=8 range=kSharpYuvRangeLimited
kSharpYuvMatrixRec709Limited,
// Kr=0.2126f Kb=0.0722f bit_depth=8 range=kSharpYuvRangeFull
kSharpYuvMatrixRec709Full,
kSharpYuvMatrixNum
} SharpYuvMatrixType;