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Based on the PNGsuite.
The following samples test various delta-image variations on rgb-color targets with an alpha channel.
In each sample the top row of images is displayed against a plain background to show the original image that is
used in delta-operations below it. A background for the remaining canvas is generated from an rgb+alpha image with
respectively 8 or 16 bits bit_depth (subsequent samples). For each a sample with a complete white and a complete
black background are shown.
Below the original images, the first 2 rows shows a pixel-replace (4) and pixel-addition (1) operation respectively.
This is only possible for rgb+alpha delta's (the last 2 original images). The next two rows show a color-replace (5)
and color-addition (2) operation respectively. This is only possible with rgb-color originals.
The bottom two rows show an alpha-replace (6) and alpha-addition (3) operation.
These are only possible with single-channel delta's (the first 5 original images).
The results will look bizar in most 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!
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