Today’s Question: Does what you say about photos saved as TIFF images [with respect to file sizes] also apply to files saved as PSD images?
Tim’s Quick Answer: Yes, TIFF and Photoshop PSD images will produce files that are of similar file sizes, all other things being equal. In both cases the file size will be significantly larger than the same image saved as a JPEG.
More Detail: Today’s question is a follow-up to a prior question that addressed TIFF images producing significantly larger file sizes than a JPEG image.
In the edition of the Ask Tim Grey eNewsletter that focused on TIFF versus JPEG file sizes, I made reference to the option to save TIFF images with compression applied. JPEG compression is always lossy, meaning some level of detail or quality will be lost in the process. However, with TIFF images you have the option to save the image with lossless compression, such as the LZW compression option that is generally available in software that enables you to save TIFF images.
The Photoshop PSD (Photoshop Document) image format is actually a TIFF container, and lossless compression is applied automatically when you save a PSD image. In that way, saving a PSD image is very similar to saving a TIFF image with the LZW compression option selected.
However, the actual compression used by PSD versus TIFF images is different, resulting in different file sizes. The actual results will vary based on the composition of the images, such as the number and type of layers used within the image.
The bottom line is that both TIFF and PSD images will produce a file size that is significantly larger than a JPEG image. Lossless compression is automatically applied with PSD files, while it is an option with TIFF images.