Investigate if we need to implement ZIP compression support

[pastelmind]

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.
• chinedufn/psd (Rust): Does not support ZIP compression (source)
• NtreevSoft/psd-parser (C#): Does not support ZIP compression (source)
• 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".