如何将YUV422转换为YUV420

Question

我想在H.264格式的相机预览中获得数据，普通相机isYv12，这样我就可以使用：

 public byte[] YV12toYUV420PackedSemiPlanar(final byte[] input, final byte[] output, final int width, final int height) 
{
    this.halfWidth = width / 2;
    this.halfHeight = height / 2;
    this.frameRate = framerate;

    this.yStride = (int) Math.ceil(width/16.0f) * 16;
    this.cStride = (int) Math.ceil(width/32.0f)  * 16;
    this.ySize = yStride * height;
    this.cSize = cStride * height / 2;

    for (int i=0; i<height; i++)
        System.arraycopy(input, yStride*i, output, yStride*i, yStride); // Y

    for (int i=0; i<halfHeight; i++) 
    {
        for (int j=0; j<halfWidth; j++)
        {
            output[ySize + (i*halfWidth + j)*2] = input[ySize + cSize + i*cStride + j]; // Cb (U)
            output[ySize + (i*halfWidth + j)*2 + 1] = input[ySize + i*cStride + j]; // Cr (V)
        }
    }
    return output;
}

但是现在我的相机预览版是yuv422，所以如何用java把YUV422转换成YUV420，我找了一些c语言的方法和理论，但是我不能成功地转换它。

我用过这个:我说得对吗？

static void yuyv_to_yuv420PackedSemiPlanar( byte[] yuyv, byte[] yuv, int w, int h ) {

    int expected_length;
    int actual_length;

    actual_length = yuyv.length;
    expected_length = PixelFormat.V4L2_PIX_FMT_YUYV.frameSize( w, h );
    if ( actual_length < expected_length ) {
        throw new IllegalArgumentException( "invalid input buffer length " + actual_length + " for yuyv image of size ( " + w + ", " + h + " ). Should be " + expected_length  );
    }

    actual_length = yuv.length;
    expected_length = PixelFormat.V4L2_PIX_FMT_RGB24.frameSize( w, h );
    if ( actual_length < expected_length ) {
        throw new IllegalArgumentException( "invalid output buffer length " + actual_length + " for yuv image of size ( " + w + ", " + h + " ). Should be " + expected_length );
    }

    for( int i = 0, j = 0; i < w * h * 3; i += 6, j += 4 ) {
        yuv[ i + 0 ] = yuyv[ j + 0 ];
        yuv[ i + 1 ] = yuyv[ j + 1 ];
        yuv[ i + 2 ] = yuyv[ j + 3 ];
        yuv[ i + 3 ] = yuyv[ j + 2 ];
        yuv[ i + 4 ] = yuyv[ j + 1 ];
        yuv[ i + 5 ] = yuyv[ j + 3 ];
    }
}

Answer 1

这是一个从YUV422 (yuyv，V4L2_PIX_FMT_YUYV，交错格式)到YUV420SP (NV21，V4L2_PIX_FMT_NV21，半平面格式)转换的代码示例。

struct pixel_yvuv {
    uint8_t Y0;
    uint8_t V;
    uint8_t Y1;
    uint8_t U;
};

struct pixel_NV21_y_plane{
    uint8_t Y0;
    uint8_t Y1;
    uint8_t Y2;
    uint8_t Y3;
};


struct pixel_NV21_uv_plane{
    uint8_t U;
    uint8_t V;
};

/*
SRC
-------
Y0V0Y1U1
Y2V1Y3U1
....
....
....
....

DST
-------
Y0Y1Y2Y3
...
...
U0V0
...
*/

void
yuyv422_to_yuv420sp(unsigned char *bufsrc, unsigned char *bufdest, int     width, int height, bool flipuv)
{
    int i,j;

    volatile struct pixel_yvuv* src;
    volatile struct pixel_NV21_y_plane* dst_p1;
    volatile struct pixel_NV21_uv_plane* dst_p2;

    src = (struct pixel_yvuv*)bufsrc;
    /* plane 1 */
    dst_p1 = (struct pixel_NV21_y_plane*) bufdest;
    /* plane 2 */
    dst_p2 = (struct pixel_NV21_uv_plane*) (bufdest + (height*width)); /* offset to UV plane */


    for(i=1; i<=height; i++)
    {
            for(j=1; j<=width/2; j++)
            {
                    if(j%2) {
                            dst_p1->Y0 = src->Y0;
                            dst_p1->Y1 = src->Y1;
                    } else {
                            dst_p1->Y2 = src->Y0;
                            dst_p1->Y3 = src->Y1;
                            dst_p1++;


                    }
                    /* vertical subsampling for U and V plane */
                    if(i%2) {
                            /* U and V  Plane */
                            if(flipuv) {
                                    dst_p2->U  = src->U;
                                    dst_p2->V  = src->V;
                            } else {
                                    dst_p2->U  = src->V;
                                    dst_p2->V  = src->U;
                            }
                            dst_p2++;
                    }
                    src++;
            }
    }
}

Answer 2

你的代码是错误的。

• 请务必了解YUV422、YUV420和YUV420SP(NV12)等YUV数据的排列方式。注意stride的含义。

YUV format

• 了解YUV映射到颜色这是调试帮助。

yuv_rgb

• 找到一个工具来显示YUV原始数据。将数据写入二进制文件，然后进行检查。

yuv-player