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56 lines
2.1 KiB
C
56 lines
2.1 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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// 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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// Returns the RGB to YUV matrix used by WebP.
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const SharpYuvConversionMatrix* SharpYuvGetWebpMatrix(void);
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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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// TODO(maryla): add 10 bits and handling of various colorspaces. Add YUV444 to
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// YUV420 conversion. Maybe also add 422 support (it's rarely used in practice,
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// especially for images).
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int SharpYuvConvert(const uint8_t* r_ptr, const uint8_t* g_ptr,
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const uint8_t* b_ptr, int step, int rgb_stride,
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uint8_t* dst_y, int dst_stride_y, uint8_t* dst_u,
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int dst_stride_u, uint8_t* dst_v, int dst_stride_v,
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int width, int height,
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const SharpYuvConversionMatrix* yuv_matrix);
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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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