Based on the PNGsuite.
The following samples test various delta-image variations on grayscale targets without an alpha channel.
In each sample the top row of images is displayed against a white background to show the original image that
is used in delta-operations below it. A background for the remaining canvas is generated from
a grayscale image with respectively 1,2,4,8 and 16 bits bit_depth (subsequent samples).
Below the original images, the first row shows a pixel-replace (4) operation and the second row shows
a pixel-addition (1) operation.
The results will look bizar in certain cases!
The left side of each sample shows a screenshot of what the right side should look like.
If they do not match, your MNG decoder doesn't handle delta-image variations very well.
Note that this will be the case for implementations using libmng-1.0.4 or older!