There is no way to use PNG transparency to generate Interlaced Masks

[lronaldo]

Interlaced Masks option requires a transparent color from the palette to generate the masks. However, this shouldn't be required, as interlaced masks do not depend on a palette color, as mask tables do. I suggest generating interlaced masks out of 3 possibilities:

• Actual transparency values from the original image (such as PNG transparency)
• An specific RGB colour in the original image (that could be different from all Amstrad CPC colours, for instance)
• A palette index colour, like now (just to let users pick this option if they wanted, even if it is not useful in general)

[AugustoRuiz]

Solved with commit:

347f905