Adobe's PSD file format document claims that there are four compression methods for image channels: uncompressed (0), RLE (1), ZIP (2), ZIP with prediction (3). However, I have yet to find a PSD file that uses compression methods 2 and 3. If they do exist, we may have to support them as well.
What to do
Attempt to find or obtain a PSD file that uses compression methods 2 and 3
Find other PSD parsers that support methods 2 or 3
Decide if we want to implement ZIP compression support
Prior art
PSD.rb (Ruby), PSD.js (CoffeeScript): Does not support ZIP compression. The author mentions that he could not produce a PSD file that uses ZIP compression.
gopsd (Go): Does not support ZIP compression (source)
libpsd (C): Does support ZIP compression (source), and uses ZLIB to do so. According to the comments in source code, "Photoshop CS and CS2 use ZIP compression".
Adobe's PSD file format document claims that there are four compression methods for image channels: uncompressed (0), RLE (1), ZIP (2), ZIP with prediction (3). However, I have yet to find a PSD file that uses compression methods 2 and 3. If they do exist, we may have to support them as well.
What to do
Prior art