SmartLockerTools/Analyser/ImageDecoder.cpp

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