Best way to compress multiple existing .psd/.psb files

[Doc_Pit]

Once I complete an image, I will save several earlier versions, which are useful in case, at a later date, I want to do some revisions.  These version files are large and  can take-up a lot of space.  I can go through these files one-by-one, take steps to reduce their size (hide layers, rasterize smart objects, etc.) and resave them with compression.  That's time consuming.  I can use the built-in Windows zip utility to group and zip multiple files.  This seems to reduce aggregate file size by about one-third.  Does anyone know of a zip utility that is especially efficient when applied to Photoshop files?

[PBArtattack · Accepted solution]

You could try 7-Zip using its native format, 7Z.

As an experiment just now, I took a 561 MB PSD and compressed it down to 311 MB with ZIP. Then I went back and compressed it with 7Z, using two different compression levels (there are five available). 7Z at "Normal" reduced the size to 245 MB; at "Ultra" it was reduced to 176 MB.

The more compression you use, the longer the process of compressing will take; it also increases the risk of corruption the higher you go although I will state that, to date, I've never had an issue with 7-Zip. On the other hand, I've never used it to compress large complex PSDs. The file I compressed at "Ultra" opened okay, though.

[Stephen Marsh · Accepted solution]

Specifically in Photoshop, you can set your File Handling Preferences to use (or not) lossless compression for PSD/PSB (saving around 1/3 size). You can also choose to include Maximise PSD and PSB File Compatibility or not which saves further space (90MB vs. 130MB in one test). Applying compression at the operating system level is another file saving with pros/cons. In all cases, one is generally trading off time for size/space.

[c.pfaffenbichler · Accepted solution]

Rasterizing Smart Objects seems like a problematic idea to me; but certain Smart Objects – namely those with only one Layer that fills the Canvas – can lose a lot of »weight« on flattening, which could be automated. 

Aside from that removing all hidden Layers and all non-composite/non-Layer Mask-Channels might also be beneficial. 

[Doc_Pit]

Thanks very much for all the responses.  I turn-off Maximise PSD and PSB Compatibility, but I have not been using compression because my files are often huge and complex (many layers).  Saving with compression takes close to the duration of my expected remaining life span.  I hate merging layers beyond what I have to because, sadly, I often think I have "finished" an image, only to decide at a later date that there are things I want to change.  Being able to go back to earlier versions with editable layers facilitates that.  But your comments help me to organize my thoughts regarding options.   I have depended on this forum for years, and I have always felt it is a gold mine.  Much appreciated.