RGB565转jpeg

RGB565是一种颜色编码格式，它使用16位来表示一个像素的颜色信息，其中5位用来表示红色分量，6位用来表示绿色分量，5位用来表示蓝色分量。而JPEG是一种图像压缩格式，它可以将图像数据压缩成较小的文件尺寸，同时保持图像质量。因此，将RGB565格式的图像转换成JPEG格式，需要进行以下步骤：

1. 将RGB565格式的图像数据解码成RGB24格式，即每个像素使用24位来表示颜色信息。这可以通过将每个像素的5位红色分量、6位绿色分量和5位蓝色分量进行扩展得到。

2. 将RGB24格式的图像数据压缩成JPEG格式。这可以使用JPEG编码库，如libjpeg等。

下面是一个使用libjpeg库将RGB565格式的图像转换成JPEG格式的示例代码：

#include <stdio.h>
#include <stdlib.h>
#include <jpeglib.h>

void rgb565_to_rgb24(unsigned char *rgb565_data, unsigned char *rgb24_data, int width, int height) {
    int i, j;
    unsigned short rgb565;
    unsigned char r, g, b;
    for (i = 0; i < height; i++) {
        for (j = 0; j < width; j++) {
            // get RGB565 color from data
            rgb565 = (rgb565_data[(i * width + j) * 2] << 8) | rgb565_data[(i * width + j) * 2 + 1];
            // expand to RGB24 format
            r = (rgb565 >> 11) << 3;
            g = ((rgb565 >> 5) & 0x3f) << 2;
            b = (rgb565 & 0x1f) << 3;
            rgb24_data[(i * width + j) * 3] = r;
            rgb24_data[(i * width + j) * 3 + 1] = g;
            rgb24_data[(i * width + j) * 3 + 2] = b;
        }
    }
}

int rgb24_to_jpeg(unsigned char *rgb24_data, int width, int height, int quality, char *filename) {
    int i, j;
    struct jpeg_compress_struct cinfo;
    struct jpeg_error_mgr jerr;
    JSAMPROW row_pointer[1];
    FILE *outfile;
    unsigned char *image_buffer;
    int image_size;

    // allocate memory for image buffer
    image_size = width * height * 3;
    image_buffer = (unsigned char *)malloc(image_size);

    // initialize JPEG compression object
    cinfo.err = jpeg_std_error(&jerr);
    jpeg_create_compress(&cinfo);

    // open output file
    if ((outfile = fopen(filename, "wb")) == NULL) {
        fprintf(stderr, "Can't open %s\n", filename);
        return 0;
    }
    jpeg_stdio_dest(&cinfo, outfile);

    // set image parameters
    cinfo.image_width = width;
    cinfo.image_height = height;
    cinfo.input_components = 3;
    cinfo.in_color_space = JCS_RGB;
    jpeg_set_defaults(&cinfo);
    jpeg_set_quality(&cinfo, quality, TRUE);

    // start compression
    jpeg_start_compress(&cinfo, TRUE);

    // write image data
    for (i = 0; i < height; i++) {
        row_pointer[0] = &rgb24_data[i * width * 3];
        jpeg_write_scanlines(&cinfo, row_pointer, 1);
    }

    // finish compression
    jpeg_finish_compress(&cinfo);

    // release resources
    fclose(outfile);
    jpeg_destroy_compress(&cinfo);
    free(image_buffer);

    return 1;
}

int main() {
    int width = 320;
    int height = 240;
    int quality = 80;
    unsigned char *rgb565_data = (unsigned char *)malloc(width * height * 2);
    unsigned char *rgb24_data = (unsigned char *)malloc(width * height * 3);
    char *filename = "output.jpg";

    // TODO: fill rgb565_data with actual data

    // convert RGB565 to RGB24
    rgb565_to_rgb24(rgb565_data, rgb24_data, width, height);

    // compress RGB24 to JPEG
    rgb24_to_jpeg(rgb24_data, width, height, quality, filename);

    // release resources
    free(rgb565_data);
    free(rgb24_data);

    return 0;
}

以上代码仅供参考，实际应用中可能需要根据具体需求进行修改。