Photoshop reads and writes IFF; PhotoCraft opened Amiga IFF/ILBM files
but had no writer. Saving as .iff now writes a FORM ILBM with a BMHD and
a ByteRun1-compressed BODY of 24 bitplanes (red, green and blue, least
significant bit first), one plane row at a time. An image with alpha
also gets a mask plane (masking 1): alpha of 128 or more is opaque, and
when any pixel is not fully opaque the export warns that alpha is
reduced to on/off transparency. Gray is expanded to RGB, 16-bit and
float images are reduced to 8 bits, and images wider or taller than
65535 pixels are refused.
The reader also opens 24-bitplane ILBMs, so a saved file reopens with
the same pixels. A transparent color index in a 24-bitplane file is
refused as unsupported.
IFF leaves ASYMMETRIC_EXCEPTIONS, Save As offers Amiga IFF, and the
codecs README, file-format parity and G10 are updated.
.CooCoo
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