Update! I always work in 16-bit mode, and it did not occur to me that the plugin would have no effect on 8-bit images (confirmed by Adobe). So the logic below is right, but the missing factor wondered about below is simple: an 8-bit image!
There is no bug in the plugin if one accepts that by design it is not supposed to work on 8-bit images, but I consider such slow Save behavior a performance bug that I hope Adobe will improve.
See my comments from two days ago on the DisallowFlateCompressedPSD plugin. This plugin can speed up saving of large Photoshop files by up to 25X faster.
Thanks to reader Ralf G who uploaded a large multi-layered file of his own for me try try.
Using Ralf’s sample file, I’ve determined that some types of files effectively disable the DisallowFlateCompressedPSD.plugin.
Comments below are with Ralf’s test file, which causes CS5 to use 12+ GB of memory when opened.
File sizes and save times
On Ralf’s file with the layers as shown, the plugin has absolutely no effect on either save time or file size. This sure seems like a bug, which I’ll ask Adobe about.
The save time drops from 121 seconds to 31 seconds when the “Background Copy” Smart Filters layer is rasterized. Even so, more than half of the 31 second figure is due to Generating Composite Image stage, which preceeds the actual save.
Even with the Smart Filters layer rasterized, the plugin is still defeated by the presence of the other layers— save time and file sizes are unchanged.
When I tested my own multi-layer files with one Levels adjustment layer, the plugin worked as expected, with its large performance gain.
My conclusion is that some combination of layers defeats the plugin (an apparent bug).
Slowness — Generating Composite Image takes a long time
The Generating Composite Image step takes 18 seconds on this test file, and there’s nothing the plugin can do about that (why it’s being generated, I’m not sure). Note that this progress dialog has a threshold for when it appears, and thus might not appear in every case, depending on the duration.
Slowness — Smart Filters layer quadruples save time
The Smart Filters layer quadruples the time to save.
With the Smart Filters layer (“Background Copy”), the Writing Large Document Format step goes for almost a full minute with very little disk I/O, and with one CPU core pegged out. Rasterizing this layer cuts the time to about 1/4 as long.