SmartLockerTools/Analyser/ImageDecoder.cpp

#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 == nullptr) {
        LOG(error) << "cannot open " << filename;
        return std::nullopt;
    }
    ImageDecoder::Image ret;
    jpeg_stdio_src(&cinfo, infile);
    jpeg_read_header(&cinfo, TRUE); // 1
    LOG(info) << "jpeg color space: " << cinfo.jpeg_color_space;
    if (cinfo.jpeg_color_space == JCS_YCbCr) {
        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);
    } else if (cinfo.jpeg_color_space == JCS_GRAYSCALE) {
        cinfo.out_color_space = JCS_GRAYSCALE; // We want grayscale 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) {
            (void)jpeg_read_scanlines(&cinfo, buffer, 1);
            memcpy(ret.data.data() + (cinfo.output_scanline - 1) * row_stride, buffer[0], row_stride);
        }
    } else {
        LOG(warning) << "jpeg color space(" << cinfo.jpeg_color_space << ") not supported.";
    }

    jpeg_destroy_decompress(&cinfo);
    fclose(infile);
    return std::make_optional(ret);
}