xvid's chroma optimizer

[plugh]

Is there a way to impliment this in a script so I can 'see' what it does?

image_chroma_optimize(IMAGE * img, int width, int height, int edged_width)
{
	int x,y;

	for (y = 1; y < height/2 - 1; y++)
	for (x = 1; x < width/2 - 1; x++)
	{
#define IS_PURE(a)  ((a)<=16||(a)>=235)
#define IMG_Y(Y,X)	img->y[(Y)*edged_width + (X)]
#define IMG_U(Y,X)	img->u[(Y)*edged_width/2 + (X)]
#define IMG_V(Y,X)	img->v[(Y)*edged_width/2 + (X)]

		if (IS_PURE(IMG_Y(y*2  ,x*2  )) &&
			IS_PURE(IMG_Y(y*2  ,x*2+1)) &&
			IS_PURE(IMG_Y(y*2+1,x*2  )) &&
			IS_PURE(IMG_Y(y*2+1,x*2+1)))
		{
			IMG_U(y,x) = (IMG_U(y,x-1) + IMG_U(y-1, x) + IMG_U(y, x+1) + IMG_U(y+1, x)) / 4;
			IMG_V(y,x) = (IMG_V(y,x-1) + IMG_V(y-1, x) + IMG_V(y, x+1) + IMG_V(y+1, x)) / 4;
		}
	}

('edged_width' is width rounded up to mod 16 plus padding...)

It doesn't have to be efficient, as I don't intend to actually run a full movie through such a script. I just want to compare before and after on some frames...