42 lines
1.5 KiB
C++
42 lines
1.5 KiB
C++
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#include "ImageDecoder.h"
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#include "BoostLog.h"
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#include <jpeglib.h>
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#include <stdio.h>
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std::optional<ImageDecoder::Image> ImageDecoder::extractJpegYComponent(const std::string &filename) {
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struct jpeg_decompress_struct cinfo;
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struct jpeg_error_mgr jerr;
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cinfo.err = jpeg_std_error(&jerr);
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jpeg_create_decompress(&cinfo);
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FILE *infile = fopen(filename.c_str(), "rb");
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if (infile == NULL) {
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LOG(error) << "cannot open " << filename;
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return std::nullopt;
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}
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ImageDecoder::Image ret;
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jpeg_stdio_src(&cinfo, infile);
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jpeg_read_header(&cinfo, TRUE);
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cinfo.out_color_space = JCS_YCbCr; // We want YCbCr color space
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jpeg_start_decompress(&cinfo);
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int row_stride = cinfo.output_width * cinfo.output_components;
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JSAMPARRAY buffer = (*cinfo.mem->alloc_sarray)((j_common_ptr)&cinfo, JPOOL_IMAGE, row_stride, 1);
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ret.width = cinfo.output_width;
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ret.height = cinfo.output_height;
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ret.data.resize(ret.width * ret.height);
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while (cinfo.output_scanline < cinfo.output_height) {
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jpeg_read_scanlines(&cinfo, buffer, 1);
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for (unsigned int i = 0; i < cinfo.output_width; ++i) {
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ret.data[(cinfo.output_scanline - 1) * cinfo.output_width + i] =
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buffer[0][i * 3]; // Y component is the first byte in YCbCr
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}
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}
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jpeg_finish_decompress(&cinfo);
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jpeg_destroy_decompress(&cinfo);
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fclose(infile);
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return std::make_optional(ret);
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}
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