NV21 to RGB conversion result in black&white

Question

I'm converting a single pixel of NV21 to RGB, it is what I did:

 public int getYUVvalue(byte[] yuv,int width,int height,int x,int y){
        int total=width*height;
    int Y=(0xff&yuv[y*width+x])-16;
    int U=(0xff&yuv[(y/2)*(width/2)+(x/2)+total])-128;
    int V=(0xff&yuv[(y/2)*(width/2)+(x/2)+total+1])-128;
    return this.convertYUVtoRGB(Y, U, V);

    }
 private static int convertYUVtoRGB(int y, int u, int v) {


        int y1192 = 1192 * y;
        int r = (y1192 + 1634 * v);
        int g = (y1192 - 833 * v - 400 * u);
        int b = (y1192 + 2066 * u);
        if (r < 0) r = 0; else if (r > 262143) r = 262143;
        if (g < 0) g = 0; else if (g > 262143) g = 262143;
        if (b < 0) b = 0; else if (b > 262143) b = 262143;


        return 0xff000000 | ((r << 6) & 0xff0000) | ((g >> 2) & 0xff00) | ((b >> 10) & 0xff);
    }

but the result is just black and white, looks like the U and V value are not correct, can someone help me with this issue? thank you!

update: I confirm my Y value is right, so I think the problem is at the U and V value, which I have no clue where the problem is. update#2: My code is very similar to decodeYUV420sp(), which is a widely used function to convert the whole image, it works perfectly, mine is just to convert a single pixel, still trying to figure out the problem by comparing it with my code. Here is the decodeyuv420sp function:

static public void decodeYUV420SP(int[] rgb, byte[] yuv420sp, int width, int height) {
        final int frameSize = width * height;

        for (int j = 0, yp = 0; j < height; j++) {
        int uvp = frameSize + (j >> 1) * width, u = 0, v = 0;
        for (int i = 0; i < width; i++, yp++) {
            int y = (0xff & ((int) yuv420sp[yp])) - 16;
            if (y < 0) y = 0;
            if ((i & 1) == 0) {
                v = (0xff & yuv420sp[uvp++]) - 128;
                u = (0xff & yuv420sp[uvp++]) - 128;
            }

            int y1192 = 1192 * y;
            int r = (y1192 + 1634 * v);
            int g = (y1192 - 833 * v - 400 * u);
            int b = (y1192 + 2066 * u);

            if (r < 0) r = 0; else if (r > 262143) r = 262143;
            if (g < 0) g = 0; else if (g > 262143) g = 262143;
            if (b < 0) b = 0; else if (b > 262143) b = 262143;

            rgb[yp] = 0xff000000 | ((r << 6) & 0xff0000) | ((g >> 2) & 0xff00) | ((b >> 10) & 0xff);
        }
    }
    } 

I still can't see where my mistake is.

update#3: problem solved, thanks for your help everyone!

Answer 1

The logic for the array indexes of U & V in the getYUVvalue function does not match the logic in decodeYUV420SP. (I count 3 differences.) Without a sample byte array in this format to test with, I can't be sure, but I think it should be:

int U=(0xff&yuv[(y/2)*width+(x&~1)+total+1])-128;
int V=(0xff&yuv[(y/2)*width+(x&~1)+total])-128;

It's missing the if (y < 0) y = 0; check also. Maybe that matters.