Rotating a flat YUV420 byte buffer

Rotating camera data means moving both the full-resolution luma samples and the lower-resolution chroma samples. A byte-array routine also depends on how those samples are laid out.

This earlier Java implementation allocates width × height × 3 / 2 bytes, rotates the luma area, and moves the remaining chroma bytes in pairs. It is a flat-buffer algorithm, not a general implementation for separate camera planes with arbitrary row and pixel strides.

The preserved routines

public static byte[] rotateYUV420Degree90(byte[] data, int imageWidth, int imageHeight) {
        byte[] yuv = new byte[imageWidth * imageHeight * 3 / 2];
        // Rotate the Y luma
        int i = 0;
        for (int x = 0; x < imageWidth; x++) {
            for (int y = imageHeight - 1; y >= 0; y--) {
                yuv[i] = data[y * imageWidth + x];
                i++;
            }
        }
        // Rotate the U and V color components
        i = imageWidth * imageHeight * 3 / 2 - 1;
        for (int x = imageWidth - 1; x > 0; x = x - 2) {
            for (int y = 0; y < imageHeight / 2; y++) {
                yuv[i] = data[(imageWidth * imageHeight) + (y * imageWidth) + x];
                i--;
                yuv[i] = data[(imageWidth * imageHeight) + (y * imageWidth) + (x - 1)];
                i--;
            }
        }
        return yuv;
    }

    private static byte[] rotateYUV420Degree180(byte[] data, int imageWidth, int imageHeight) {
        byte[] yuv = new byte[imageWidth * imageHeight * 3 / 2];
        int i = 0;
        int count = 0;
        for (i = imageWidth * imageHeight - 1; i >= 0; i--) {
            yuv[count] = data[i];
            count++;
        }
        i = imageWidth * imageHeight * 3 / 2 - 1;
        for (i = imageWidth * imageHeight * 3 / 2 - 1; i >= imageWidth
                * imageHeight; i -= 2) {
            yuv[count++] = data[i - 1];
            yuv[count++] = data[i];
        }
        return yuv;
    }

    public static byte[] rotateYUV420Degree270(byte[] data, int imageWidth,
                                               int imageHeight) {
        byte[] yuv = new byte[imageWidth * imageHeight * 3 / 2];
        int nWidth = 0, nHeight = 0;
        int wh = 0;
        int uvHeight = 0;
        if (imageWidth != nWidth || imageHeight != nHeight) {
            nWidth = imageWidth;
            nHeight = imageHeight;
            wh = imageWidth * imageHeight;
            uvHeight = imageHeight >> 1;// uvHeight = height / 2
        }
        // ??Y
        int k = 0;
        for (int i = 0; i < imageWidth; i++) {
            int nPos = 0;
            for (int j = 0; j < imageHeight; j++) {
                yuv[k] = data[nPos + i];
                k++;
                nPos += imageWidth;
            }
        }
        for (int i = 0; i < imageWidth; i += 2) {
            int nPos = wh;
            for (int j = 0; j < uvHeight; j++) {
                yuv[k] = data[nPos + i];
                yuv[k + 1] = data[nPos + i + 1];
                k += 2;
                nPos += imageWidth;
            }
        }
        return rotateYUV420Degree180(yuv, imageWidth, imageHeight);
    }

The 270-degree routine composes its work with the 180-degree routine. Validate dimensions, input length, chroma order, and the destination width/height convention before adapting it. No camera frames were processed for this revision.

Source: original Gist revision.

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