if (image->HasMask())
mask_key = (image->GetMaskRed() << 16) |
(image->GetMaskGreen() << 8) | image->GetMaskBlue();
// 2b. generate colour table:
if (image->HasMask())
mask_key = (image->GetMaskRed() << 16) |
(image->GetMaskGreen() << 8) | image->GetMaskBlue();
// 2b. generate colour table: