Why is the media sample upside down after convert its buffer data from YUV to RGB?

Question

I converted the buffer of a media sample from YUY2 to RGB24 pixel by pixel, and then I got a upside-down image. What's wrong with it?

Answer

The definition of the biHeight field of BITMAPINFOHEADER depends the the biCompression field of BITMAPINFOHEADER.

If the bitmap is uncompressed RGB format, the positive biHeight value means the image is bottom-up image; if the bitmap is one of YUV formats such as YUY2, UYVY, and YV12, the image is top-down oriented and the sign of biHeight value must be ignored.

So, I need to do a vertical flip to get a correct image after convert buffer data from YUY2 to RGB24.

You can get more detail information in FOURCC.org: Bitmap Orientation and biHeight