jerem/psdparse — pull request #4 by palange (2012-05-30 05:36:09+00:00)
Title: Support for Alpha channel in PSD merged image data.

1. Using '>h' to read signed short for layer count.
2. Reading 'RGBA' for merged data with channel count 4,
and color mode 3.

For a PSD with transparency a negative layer count in
the layer info struct its absolute value is the number
of layers and the first alpha channel contains the
transparency data for the merged result.

According to:
http://www.adobe.com/devnet-apps/photoshop/fileformatashtml/PhotoshopFileFormats.htm#50577409_16000