| // Copyright 2022 Google Inc. All Rights Reserved. | |
| // | |
| // Use of this source code is governed by a BSD-style license | |
| // that can be found in the COPYING file in the root of the source | |
| // tree. An additional intellectual property rights grant can be found | |
| // in the file PATENTS. All contributing project authors may | |
| // be found in the AUTHORS file in the root of the source tree. | |
| // ----------------------------------------------------------------------------- | |
| // | |
| // Sharp RGB to YUV conversion. | |
| extern "C" { | |
| // This explicitly marks library functions and allows for changing the | |
| // signature for e.g., Windows DLL builds. | |
| // SharpYUV API version following the convention from semver.org | |
| // Version as a uint32_t. The major number is the high 8 bits. | |
| // The minor number is the middle 8 bits. The patch number is the low 16 bits. | |
| // Returns the library's version number, packed in hexadecimal. See | |
| // SHARPYUV_VERSION. | |
| 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. | |
| typedef struct { | |
| int rgb_to_y[4]; | |
| int rgb_to_u[4]; | |
| int rgb_to_v[4]; | |
| } SharpYuvConversionMatrix; | |
| // Converts RGB to YUV420 using a downsampling algorithm that minimizes | |
| // artefacts caused by chroma subsampling. | |
| // This is slower than standard downsampling (averaging of 4 UV values). | |
| // Assumes that the image will be upsampled using a bilinear filter. If nearest | |
| // neighbor is used instead, the upsampled image might look worse than with | |
| // standard downsampling. | |
| // r_ptr, g_ptr, b_ptr: pointers to the source r, g and b channels. Should point | |
| // to uint8_t buffers if rgb_bit_depth is 8, or uint16_t buffers otherwise. | |
| // rgb_step: distance in bytes between two horizontally adjacent pixels on the | |
| // r, g and b channels. If rgb_bit_depth is > 8, it should be a | |
| // multiple of 2. | |
| // rgb_stride: distance in bytes between two vertically adjacent pixels on the | |
| // r, g, and b channels. If rgb_bit_depth is > 8, it should be a | |
| // multiple of 2. | |
| // rgb_bit_depth: number of bits for each r/g/b value. One of: 8, 10, 12, 16. | |
| // Note: 16 bit input is truncated to 14 bits before conversion to yuv. | |
| // yuv_bit_depth: number of bits for each y/u/v value. One of: 8, 10, 12. | |
| // y_ptr, u_ptr, v_ptr: pointers to the destination y, u and v channels. Should | |
| // point to uint8_t buffers if yuv_bit_depth is 8, or uint16_t buffers | |
| // otherwise. | |
| // y_stride, u_stride, v_stride: distance in bytes between two vertically | |
| // 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 | |
| SHARPYUV_EXTERN int SharpYuvConvert(const void* r_ptr, const void* g_ptr, | |
| const void* b_ptr, int rgb_step, | |
| int rgb_stride, int rgb_bit_depth, | |
| void* y_ptr, int y_stride, void* u_ptr, | |
| int u_stride, void* v_ptr, int v_stride, | |
| int yuv_bit_depth, int width, int height, | |
| const SharpYuvConversionMatrix* yuv_matrix); | |
| // TODO(b/194336375): Add YUV444 to YUV420 conversion. Maybe also add 422 | |
| // support (it's rarely used in practice, especially for images). | |
| } // extern "C" | |