Today’s Question: Does this technique make sense? “Placing a blank, white layer atop a .PSD can cut the file size in half?”
Tim’s Quick Answer: No, not really. This “trick” may have worked in older versions of Photoshop (or the person who tested it wasn’t being very methodical), but I’ve not been able to reproduce the effect in recent versions of Photoshop. But regardless, the real issue here (from what I can gather) is the “Maximize Compatibility” setting in Preferences, which when enabled will approximately double the base file size for PSD images.
More Detail: When I read about this technique, I immediately suspected the underlying issue related to the Maximize Compatibility option. Specifically, the white layer atop the stack of layers on the Layers panel would cause the preview for the image to be entirely white, which would result in a preview that compresses better and thus produces a smaller overall file size.
However, that approach would completely defeat the whole purpose of having the Maximize Compatibility feature turned on in the first place. The reason the Maximize Compatibility option causes the file size to double (compared to a flattened original image) is that this option causes a full-resolution composite preview of the image to be embedded. This allows other applications to see the actual appearance of the image without having to understand the various underlying layers that are specific to Photoshop.
However, rather than using this “trick”, you can simply turn off the Maximize Compatibility option in the first place. That way, rather than having a blank white preview you will have no preview at all, causing the file size to be approximately half of what it otherwise would have been with Maximize Compatibility turned on.
Keep in mind, however, that by turning off Maximize Compatibility for the PSD files you save, you won’t be able to see previews of those images with other applications that might otherwise be able to show a preview. You also won’t be able to import PSD files into Lightroom if Maximize Compatibility is turned off.
You can choose whether you want the Maximize Compatibility option enabled in the File Handling section of the Preferences dialog in Photoshop. I generally leave the option set to “Ask” so I can choose whether to enable Maximize Compatibility based on how I’ll be using the PSD file.