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82 lines
3.7 KiB
C
82 lines
3.7 KiB
C
// Copyright 2022 Google Inc. All Rights Reserved.
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//
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// Use of this source code is governed by a BSD-style license
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// that can be found in the COPYING file in the root of the source
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// tree. An additional intellectual property rights grant can be found
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// in the file PATENTS. All contributing project authors may
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// be found in the AUTHORS file in the root of the source tree.
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// -----------------------------------------------------------------------------
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//
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// Sharp RGB to YUV conversion.
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#ifndef WEBP_SHARPYUV_SHARPYUV_H_
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#define WEBP_SHARPYUV_SHARPYUV_H_
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#include <inttypes.h>
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#ifdef __cplusplus
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extern "C" {
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#endif
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// SharpYUV API version following the convention from semver.org
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#define SHARPYUV_VERSION_MAJOR 0
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#define SHARPYUV_VERSION_MINOR 1
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#define SHARPYUV_VERSION_PATCH 0
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// Version as a uint32_t. The major number is the high 8 bits.
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// The minor number is the middle 8 bits. The patch number is the low 16 bits.
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#define SHARPYUV_MAKE_VERSION(MAJOR, MINOR, PATCH) \
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(((MAJOR) << 24) | ((MINOR) << 16) | (PATCH))
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#define SHARPYUV_VERSION \
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SHARPYUV_MAKE_VERSION(SHARPYUV_VERSION_MAJOR, SHARPYUV_VERSION_MINOR, \
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SHARPYUV_VERSION_PATCH)
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// RGB to YUV conversion matrix, in 16 bit fixed point.
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// y = rgb_to_y[0] * r + rgb_to_y[1] * g + rgb_to_y[2] * b + rgb_to_y[3]
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// u = rgb_to_u[0] * r + rgb_to_u[1] * g + rgb_to_u[2] * b + rgb_to_u[3]
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// v = rgb_to_v[0] * r + rgb_to_v[1] * g + rgb_to_v[2] * b + rgb_to_v[3]
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// Then y, u and v values are divided by 1<<16 and rounded.
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typedef struct {
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int rgb_to_y[4];
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int rgb_to_u[4];
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int rgb_to_v[4];
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} SharpYuvConversionMatrix;
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// Converts RGB to YUV420 using a downsampling algorithm that minimizes
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// artefacts caused by chroma subsampling.
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// This is slower than standard downsampling (averaging of 4 UV values).
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// Assumes that the image will be upsampled using a bilinear filter. If nearest
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// neighbor is used instead, the upsampled image might look worse than with
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// standard downsampling.
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// r_ptr, g_ptr, b_ptr: pointers to the source r, g and b channels. Should point
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// to uint8_t buffers if rgb_bit_depth is 8, or uint16_t buffers otherwise.
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// rgb_step: distance in bytes between two horizontally adjacent pixels on the
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// r, g and b channels. If rgb_bit_depth is > 8, it should be a
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// multiple of 2.
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// rgb_stride: distance in bytes between two vertically adjacent pixels on the
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// r, g, and b channels. If rgb_bit_depth is > 8, it should be a
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// multiple of 2.
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// rgb_bit_depth: number of bits for each r/g/b value. One of: 8, 10, 12, 16.
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// Note: 16 bit input is truncated to 14 bits before conversion to yuv.
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// yuv_bit_depth: number of bits for each y/u/v value. One of: 8, 10, 12.
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// y_ptr, u_ptr, v_ptr: pointers to the destination y, u and v channels. Should
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// point to uint8_t buffers if yuv_bit_depth is 8, or uint16_t buffers
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// otherwise.
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// y_stride, u_stride, v_stride: distance in bytes between two vertically
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// adjacent pixels on the y, u and v channels. If yuv_bit_depth > 8, they
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// should be multiples of 2.
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// width, height: width and height of the image in pixels
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int SharpYuvConvert(const void* r_ptr, const void* g_ptr, const void* b_ptr,
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int rgb_step, int rgb_stride, int rgb_bit_depth,
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void* y_ptr, int y_stride, void* u_ptr, int u_stride,
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void* v_ptr, int v_stride, int yuv_bit_depth, int width,
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int height, const SharpYuvConversionMatrix* yuv_matrix);
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// TODO(b/194336375): Add YUV444 to YUV420 conversion. Maybe also add 422
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// support (it's rarely used in practice, especially for images).
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#ifdef __cplusplus
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} // extern "C"
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#endif
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#endif // WEBP_SHARPYUV_SHARPYUV_H_
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