y2rgb.cpp

#include <iostream>

#ifdef __ARM_NEON

#include <arm_neon.h>

#endif

#include <fstream>

void gray2RgbRow(const uint8_t *gray, uint8_t *rgb, int n) {
    int i = 0;

#ifdef __ARM_NEON
    const int vsize = 16;
    for (; i <= n - vsize; i += vsize, gray += vsize, rgb += vsize * 3) {
        uint8x16_t g = vld1q_u8(gray);
        uint8x16x3_t v{g, g, g};
        vst3q_u8(rgb, v);
    }
#endif
    for (; i < n; i++, gray++, rgb += 3) {
        rgb[0] = rgb[1] = rgb[2] = gray[0];
    }
}

int YToRGB24(const uint8_t *src_y,
             int src_stride_y,
             const uint8_t *src_vu,
             int src_stride_vu,
             uint8_t *dst_rgb24,
             int dst_stride_rgb24,
             int width,
             int height) {

    for (int y = 0; y < height; ++y) {
        gray2RgbRow(src_y, dst_rgb24, width);
        dst_rgb24 += dst_stride_rgb24;
        src_y += src_stride_y;
    }
    return 0;
}

int main() {
    //created with
    // # ffmpeg -i headshot1024.jpg -pix_fmt yuv420p -f rawvideo headshot1024.yuv420p
    const std::string inputFile = "headshot1024.yuv420p";
    std::ifstream infile(inputFile, std::ios_base::binary);

    std::vector<uint8_t> buffer{std::istreambuf_iterator<char>(infile),
                                std::istreambuf_iterator<char>()};
    int w = 1024;
    int h = 790;
    uint8_t rgb[1024 * 790 * 3] = {};
    YToRGB24(buffer.data(), w, nullptr, 0, rgb, w * 3, w, h);

    std::ofstream out("headshot1024.rgb", std::ios::binary);
    out.write((char *) &rgb[0], sizeof(rgb));
    out.close();
    // to open image use
    // # ffmpeg  -s 1024x790 -f rawvideo -pix_fmt rgb24  -i headshot1024.rgb -vframes 1 headshot1024.rgb.png

}