Rotate YUV420Sp image by 90 degrees counter clockwise

Question

I want to rotate YUV420SP image by 90 counter clockwise. Image size is 640*480, so the rotated image size becomes 480*640 which i don't want, So i want to extract 480*480 data (or any other square size) and rotate that data.

I have seen : Rotate an YUV byte array on Android

But this answer rotates 90 clockwise.

Can somebody suggest some function which rotates YUV420Sp data by 90(counter clockwise) or by 270 degrees (clockwise) without changing image dimensions.

Answer 1

OK, here's my native code that evolved after much banging of the head.

My difficulty was that I didn't understand planar image formats until I saw this and this:

Here are the 2 functions I eventually wrote:

// rotate luma image plane 90*
//
//             (dst direction)
//                 ------>
//      dst -> +-------------+
//             |^            |
//             |^ (base dir) |
//             |^            |
//     base -> +-------------+ <- endp
//
//////////////////////////////////////////////////////////
void rotateLumaPlane90(const unsigned char *src, unsigned char *dst,
                       size_t size, size_t width, size_t height)
{
    const unsigned char *endp;
    const unsigned char *base;
    int j;

    endp = src + size;
    for (base = endp - width; base < endp; base++) {
        src = base;
        for (j = 0; j < height; j++, src -= width)
        {
            *dst++ = *src;
        }

    }
}


//
// nv12 chroma plane is interleaved chroma values that map
// from one pair of chroma to 4 pixels:
//
// Y1 Y2 Y3 Y4
// Y5 Y6 Y7 Y8   U1,V1 -> chroma values for block  Y1 Y2
// Y9 Ya Yb Yc                                     Y5 Y6
// Yd Ye Yf Yg
// -----------   U2,V2 -> chroma values for block  Y3 Y4
// U1 V1 U2 V2                                     Y7 Y8
// U3 V3 U4 V4
//
//////////////////////////////////////////////////////////
void rotateChromaPlane90(const unsigned char *src, unsigned char *dst,
                         size_t size, size_t width, size_t height)
{
    // src will start at upper right, moving down to bottom
    // then left 1 col and down...
    //
    // dest will start at end and go to 0

    int row = 0;
    int col = (int) width;
    int src_offset = col - 1;
    int dst_offset = (int) size - 2;

    while (src_offset >= 0)
    {
        dst[dst_offset] = src[src_offset];
        dst[dst_offset+1] = src[src_offset+1];
        dst_offset -= 2;

        src_offset += width;
        row++;

        if (row >= height) {
            col -= 2;
            src_offset = col;
            row = 0;
        }
    }
}

And here is a sample of me calling these funcs from android native:

  // first rotate the Y plane
  rotateLumaPlane90((unsigned char *) encode_buffer, 
                     rotate_buffer, 
                     yPlaneSize,
                     gInputWidth, 
                     gInputHeight);


  // now rotate the U and V planes
  rotateChromaPlane90((unsigned char *) encode_buffer + yPlaneSize,
                       rotate_buffer + yPlaneSize,
                       yPlaneSize / 2,
                       gInputWidth,
                       gInputHeight/2);

Notice the last param to the rotateChromaPlane90 is the height of the original image/2. I should probably just change the chroma rotate function to make that less error-prone.

When flipped to the back facing camera I then found I needed to rotate 90* in the opposite direction (or 270*) so I also have a 270* variation as:

// rotate luma image plane 270*
//
//             +-------------+
//             |^            |
//             |^ (base dir) |
//             |^            |
//     base -> +-------------+ <- endp
//                          ^
//             <----------  |
//              (dst dir)  dst
//
//////////////////////////////////////////////////////////
void rotateLumaPlane270(unsigned char *src,
                        register unsigned char *dst,
                        int size, int width, int height)
{
    unsigned char *endp;
    register unsigned char *base;
    int j;

    endp = src + size;
    dst = dst + size - 1;
    for (base = endp - width; base < endp; base++) {
        src = base;
        for (j = 0; j < height; j++, src -= width)
        {
            *dst-- = *src;
        }

    }
}

//
// nv21 chroma plane is interleaved chroma values that map
// from one pair of chroma to 4 pixels:
//
// Y1 Y2 Y3 Y4
// Y5 Y6 Y7 Y8   U1,V1 -> chroma values for block  Y1 Y2
// Y9 Ya Yb Yc                                     Y5 Y6
// Yd Ye Yf Yg
// -----------   U2,V2 -> chroma values for block  Y3 Y4
// U1 V1 U2 V2                                     Y7 Y8
// U3 V3 U4 V4
//
//////////////////////////////////////////////////////////
void rotateChromaPlane270(unsigned char *src,
                          register unsigned char *dst,
                          int size, int width, int height)
{
    // src will start at upper right, moving down to bottom
    // then left 1 col and down...
    //
    // dest will start at 0 and go til end

    int row = 0;
    int col = width;
    int src_offset = col - 1;
    int dst_offset = 0;

    while (src_offset > 0)
    {
      dst[dst_offset++] = src[src_offset];
      dst[dst_offset++] = src[src_offset+1];

      src_offset += width;
      row++;

      if (row >= height) {
        col -= 2;
        src_offset = col;
        row = 0;
      }
    }
}