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These options allow you to skip one bitplane worth of graphics data. This is useful for blitter objects (bobs) where the game will often store the data in Amiga ACBM format with an extra bitplane used as a mask:

  • Mask before graphics - Skip a bitplane worth of graphics data before extracting graphics
  • Mask after graphics - Skip a bitplane worth of graphics data after extracting graphics

It is usually very easy to recognise when a mask is required if the rip width ends up being a multiple of the bitplane width. For example, Commando uses 32x25 bobs, and they are 4 colours with a mask before the graphics. With a rip width of 320 pixels and 1 bitplane, you will see the following:

Commando bobs 1 bitplane

The solid white block every 5 bitplanes is a dead giveaway that the game is really 4 bitplanes and a mask. If you set the bitplanes to 4, you will see that every 5th graphic is correct, as the mask is ignored. But all the other graphics are wrong:

Commando bobs 4 bitplanes without mask

Increasing the bitplanes to 5 will give a consistent but incorrect palette, as the game is now using the full 32 colour palette when in actual fact the game is only 16 colours:

Commando bobs 5 bitplanes without mask

Set the bitplanes to 4 and tick the Mask Before Graphics checkbox to extract the correct graphics:

Commando bobs 4 bitplanes with mask before graphics

If the game has the mask after all the graphics, simply use the Mask After Graphics checkbox instead.

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