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libjpeg学习4:libjpeg-turbo之YUV

libjpeg-turbo支持直接从JPEG解压成YUV格式,或者反之。这也是我当初想研究它的一个动力。

看了头文件注释,它是支持YUV444(即宏TJSAMP_444),YUV422(即宏TJSAMP_422),YUV420(即宏TJSAMP_420),YUV400(即宏TJSAMP_440),YUV411(即宏TJSAMP_411)。可惜的是,只支持平面格式(plane),对于交织的如UYVY或特别的如NV12(即YUV420SP)或NV16(即YUV422SP),都没看到有支持。在sourceforge上看邮件列表,发现有些描述,但还没研究过,看发布的源码,也未见有说明,估计是不支持的。

本文简单介绍如何从JPEG解压成YUV格式,以及如何将YUV压缩成JPEG。

libjpeg-turbo使用tjBufSizeYUV2函数计算YUV大小,开始时没注意第二个参数pad,默认传递0,发现没效果,而传1或4,却是可以的。解压后的YUV的格式,是由JPEG图片的采样格式决定的,如果JPEG本身是YUV420,则解压得到的YUV,就是YUV420格式。

示例代码如下:

int tjpeg2yuv(unsigned char* jpeg_buffer, int jpeg_size, unsigned char** yuv_buffer, int* yuv_size, int* yuv_type)
{
    tjhandle handle = NULL;
    int width, height, subsample, colorspace;
    int flags = 0;
    int padding = 1; // 1或4均可,但不能是0
    int ret = 0;

    handle = tjInitDecompress();
    tjDecompressHeader3(handle, jpeg_buffer, jpeg_size, &width, &height, &subsample, &colorspace);

    printf("w: %d h: %d subsample: %d color: %d\n", width, height, subsample, colorspace);
    
    flags |= 0;
    
    *yuv_type = subsample;
    // 注:经测试,指定的yuv采样格式只对YUV缓冲区大小有影响,实际上还是按JPEG本身的YUV格式来转换的
    *yuv_size = tjBufSizeYUV2(width, padding, height, subsample);
    *yuv_buffer =(unsigned char *)malloc(*yuv_size);
    if (*yuv_buffer == NULL)
    {
        printf("malloc buffer for rgb failed.\n");
        return -1;
    }

    ret = tjDecompressToYUV2(handle, jpeg_buffer, jpeg_size, *yuv_buffer, width,
			padding, height, flags);
    if (ret < 0)
    {
        printf("compress to jpeg failed: %s\n", tjGetErrorStr());
    }
    tjDestroy(handle);

    return ret;
}

int tyuv2jpeg(unsigned char* yuv_buffer, int yuv_size, int width, int height, int subsample, unsigned char** jpeg_buffer, unsigned long* jpeg_size, int quality)
{
    tjhandle handle = NULL;
    int flags = 0;
    int padding = 1; // 1或4均可,但不能是0
    int need_size = 0;
    int ret = 0;

    handle = tjInitCompress();
   
    flags |= 0;

    need_size = tjBufSizeYUV2(width, padding, height, subsample);
    if (need_size != yuv_size)
    {
        printf("we detect yuv size: %d, but you give: %d, check again.\n", need_size, yuv_size);
        return 0;
    }

    ret = tjCompressFromYUV(handle, yuv_buffer, width, padding, height, subsample, jpeg_buffer, jpeg_size, quality, flags);
    if (ret < 0)
    {
        printf("compress to jpeg failed: %s\n", tjGetErrorStr());
    }

    tjDestroy(handle);

    return ret;
}

另外,该库也支持从RGB转换成YUV,或反之。调用相应的函数即可,不再详述。示例代码如下:

int trgb2yuv(unsigned char* rgb_buffer, int width, int height, unsigned char** yuv_buffer, int* yuv_size, int subsample)
{
    tjhandle handle = NULL;
    int flags = 0;
    int padding = 1; // 1或4均可,但不能是0
    int pixelfmt = TJPF_RGB;
    int ret = 0;

    handle = tjInitCompress();
   
    flags |= 0;

    *yuv_size = tjBufSizeYUV2(width, padding, height, subsample);

    *yuv_buffer =(unsigned char *)malloc(*yuv_size);
    if (*yuv_buffer == NULL)
    {
        printf("malloc buffer for rgb failed.\n");
        return -1;
    }
    ret = tjEncodeYUV3(handle, rgb_buffer, width, 0, height, pixelfmt, *yuv_buffer, padding, subsample, flags);
    if (ret < 0)
    {
        printf("encode to yuv failed: %s\n", tjGetErrorStr());
    }

    tjDestroy(handle);

    return ret;
}

int tyuv2rgb(unsigned char* yuv_buffer, int yuv_size, int width, int height, int subsample, unsigned char** rgb_buffer, int* rgb_size)
{
    tjhandle handle = NULL;
    int flags = 0;
    int padding = 1; // 1或4均可,但不能是0
    int pixelfmt = TJPF_RGB;
    int need_size = 0;
    int ret = 0;

    handle = tjInitDecompress();
   
    flags |= 0;

    need_size = tjBufSizeYUV2(width, padding, height, subsample);
    if (need_size != yuv_size)
    {
        printf("we detect yuv size: %d, but you give: %d, check again.\n", need_size, yuv_size);
        return -1;
    }

    *rgb_size = width*height*tjPixelSize[pixelfmt];

    *rgb_buffer =(unsigned char *)malloc(*rgb_size);
    if (*rgb_buffer == NULL)
    {
        printf("malloc buffer for rgb failed.\n");
        return -1;
    }
    ret = tjDecodeYUV(handle, yuv_buffer, padding, subsample, *rgb_buffer, width, 0, height, pixelfmt, flags);
    if (ret < 0)
    {
        printf("decode to rgb failed: %s\n", tjGetErrorStr());
    }

    tjDestroy(handle);

    return ret;
}

以上代码示例,二级指针均在函数内分配内存,需要调用者自行释放,否则会有内存泄漏。

李迟 7.8


本文固定链接: http://www.latelee.org/programming-under-linux/libjpeg-learning4-libjpeg-turbo2yuv.html

如无特别说明,迟思堂工作室文章均为原创,转载请注明: libjpeg学习4:libjpeg-turbo之YUV | 迟思堂工作室

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