What's an efficient way to tell if a bitmap is entirely black?

Question

I\'m wondering if there\'s a super-efficient way of confirming that an Image object references an entirely black image, so every pixel within the bitmap is ARGB(255, 0, 0, 0).

Answer 1

Draw the bitmap with a ColorMatrix that has 3 x 255 in the diagonal, that will blow any non-black pixel to pure white. Then draw that bitmap to a smaller one whose width is a multiple of 4 and has the Format24bppRgb format. That eliminates the alpha, reduces the size and leaves only zeros if the bitmap is truly black.

You'll have to experiment to see how small you can make the bitmap, use a sample one that has only one white pixel to see when the interpolator makes it disappear. I'm guessing you can go pretty far.