A .psb file is one of the ones people send over when nothing on their machine will open it. If a large file opens slowly, it is almost always the composite read, not the layer data.
The structure, briefly
Same header layout as PSD but version 2 in the version field; dimensions and channel counts are stored as 8-byte values instead of 4.
Telling a real file from a renamed one
Read 4 bytes and you know: 38 42 50 53. A mismatch means the .psb file was renamed, which is the most common thing we see.
Programs that open it
Installed options: Adobe Photoshop, Affinity Photo, GIMP 2.10+, Adobe Camera Raw (open as image). None of them have to be the program that made the file: Universal Viewer reads it and writes nothing back.
When you have to convert
The targets people actually ask for are .png, .jpg, .pdf, .tif. Each one has its own page with the settings that matter: psb → png, psb → jpg, psb → pdf, psb → tif
M. Halvorsen re-read this on 2026-10-05.
Notes from the file library
Files of this kind are catalogued with the family named in the table above. The family groups them by what a file carries, not by the application that wrote it, which is why two extensions from the same application can sit in different families.
Two things decide whether a file can be opened on a machine that never had the application that made it: the header, which says what the container is, and the structure behind it, which says whether the contents can be read at all. The conversion guides listed on the page cover the targets that come up most often.
Format pages are rebuilt with each release of the toolset, and the review line at the bottom of the page is when an editor last checked the entry against a file. If a page disagrees with a file you have, send the first sixteen bytes and the build number to the support address and the entry is corrected in the next build.