Today’s Question: In your answer about the “Maximize Compatibility” feature for Photoshop PSD files you also mentioned “PSB” files. I’m familiar, of course, with the PSD format that is a standard part of Photoshop, but what are PSB files?
Tim’s Quick Answer: The Photoshop PSB file format supports larger file sizes than the Photoshop PSD format. PSD files are limited to a maximum of 30,000 pixels on a side, while PSB files can be up to 300,000 pixels on a side.
More Detail: For most photographers with most images, the Photoshop PSD (or Photoshop Document) file format will be perfectly suitable for their needs. A PSD file is obviously capable of preserving all the various features of Photoshop, such as layers, layer masks, saved selections and more. However, a PSD file is limited to 30,000 pixels on the long side, so in some cases it may not support an image you want to save.
Of course, 30,000 pixels on the long side is still a rather large image. At a typical print resolution of 300 pixels per inch an image that is 30,000 across can be printed 100-inches wide. That’s a print that is more than eight feet wide, so it is certainly what most photographers would call a large image.
However, there are situations where you may need to produce a larger image, such as to print a very large composite panorama. If an image exceeds 30,000 pixels in either dimension, you’ll need to save it in the Photoshop PSB (as in “big”) file format. Note that Photoshop only supports image dimensions of up to 300,000 pixels, which in turn represents the maximum pixel dimensions for PSB files. Of course, this really is a quite large image size, with 300,000 pixels across representing a print size of about 1,000 inches or more than 83 feet based on a typical print resolution of 300 pixels per inch.
For photographers using Lightroom Classic to manage their photos it is important to keep in mind that with Lightroom Classic the maximum pixel dimensions are 65,000 pixels on a side. In other words, while you can save a PSB file in Photoshop with up to 300,000 pixels on a side, images above 65,000 pixels on a side can’t be imported into Lightroom Classic.