The short answer
- PSB is an image-design format that stores very large Photoshop documents with layers, masks, effects, transparency and HDR data, with dimensions limited to 300,000 pixels in either direction.
- Open a PSB file in a current Adobe Photoshop release, the reference application for viewing and editing its layers and other Photoshop features. If another application, an older Photoshop release or a plug-in fails, check whether the file exceeds 2 GB or 30,000 pixels in width or height.
- PSB has no identified executable active-content mechanism, but an untrusted file can declare extremely large dimensions and contain complex compressed layers or metadata. Use a current reader and treat unexpected memory use, decompression failures or malformed sections as warning signs.
PSB File: Identify, Open and Convert Photoshop Large Documents
Adobe Photoshop Large Document, or PSB, is Photoshop’s native format for oversized documents. Its big-endian binary structure begins with ASCII “8BPS” and version 2, then stores color-mode data, resources, layer-and-mask information and image data. It supports 1–56 channels and 1-, 8-, 16- or 32-bit channel depth.
Choose the destination according to what must survive. A conventional raster export can flatten separate layers; JPEG also loses image information through lossy compression, and Photoshop Raw removes layers. Keep the original PSB when layers, masks, effects or full editability matter.
How to open it
Open a PSB file in a current Adobe Photoshop release, the reference application for viewing and editing its layers and other Photoshop features. If another application, an older Photoshop release or a plug-in fails, check whether the file exceeds 2 GB or 30,000 pixels in width or height.
Open a PSB file in a current Adobe Photoshop release, the reference application for viewing and editing its layers and other Photoshop features. If another application, an older Photoshop release or a plug-in fails, check whether the file exceeds 2 GB or 30,000 pixels in width or height.
Choose the destination according to what must survive. A conventional raster export can flatten separate layers; JPEG also loses image information through lossy compression, and Photoshop Raw removes layers. Keep the original PSB when layers, masks, effects or full editability matter.
File safety
PSB has no identified executable active-content mechanism, but an untrusted file can declare extremely large dimensions and contain complex compressed layers or metadata. Use a current reader and treat unexpected memory use, decompression failures or malformed sections as warning signs.
An unknown sender, a name ending in two extensions, or contents that do not match the extension — check before you open it.
Converting it
Choose the destination according to what must survive. A conventional raster export can flatten separate layers; JPEG also loses image information through lossy compression, and Photoshop Raw removes layers. Keep the original PSB when layers, masks, effects or full editability matter.
Convert a copy, never the original, then compare quality, metadata, and layout against what you started with.
Common questions
What is a PSB file used for in Adobe Photoshop?
A PSB file stores a very large Photoshop document while preserving layers, effects, filters, masks, transparency and 32-bit HDR image data. It supports images as large as 300,000 pixels in either direction.
How do I open a PSB file in Photoshop?
Use a current Adobe Photoshop release and open the PSB as a document. Photoshop is the reference application for viewing and editing the format’s layers and other native features.
How do I open a PSB file on Windows?
Install or use a current Windows release of Adobe Photoshop, then open the PSB from Photoshop. Other applications and older releases may fail, particularly when the document exceeds 2 GB.
How do I open a PSB file on a Mac?
Open the PSB with a current macOS release of Adobe Photoshop. If an older release or plug-in rejects it, check the file size and whether either dimension exceeds 30,000 pixels.
Can I open a PSB file on a phone?
Do not assume that a phone application supports PSB. Compatibility outside current Photoshop releases is limited, especially for files over 2 GB or documents wider or taller than 30,000 pixels; use current desktop Photoshop when faithful access is required.
Why will my PSB file not open or report that it is unsupported?
The reader may not support PSB version 2, the file may exceed its size or dimension limits, or a section may be malformed. Confirm the header begins with “8BPS” followed by version 2, then try a current Photoshop release.
What is the difference between PSB and PSD, and which should I use?
Use PSB for Photoshop documents that require the Large Document Format limits. PSB uses the “8BPS” signature with version 2, whereas the closely related PSD uses version 1; PSB has more limited compatibility outside current Photoshop releases.
Can I convert PSB to JPEG without losing layers?
No. A JPEG export does not preserve PSB’s separate Photoshop layers and also discards image information through lossy compression. Retain the original PSB if layers or later editing matter.
Is an untrusted PSB file safe to open?
PSB has no identified executable active-content mechanism, but it can contain extremely large images, compressed layers and complex metadata. A malformed file can stress a reader or exhaust resources, so open untrusted files only with a current application and adequate system resources.
What are the PSB size, channel and bit-depth limits?
PSB supports dimensions up to 300,000 pixels in either direction, 1–56 channels, and depths of 1, 8, 16 or 32 bits per channel. Application and plug-in limits may be lower.
Related formats
Sources
Adobe Photoshop File Formats Specification · Adobe — official format developer specification
Save large documents in Photoshop · Adobe — official Photoshop documentation
Image file formats supported in Photoshop · Adobe — official Photoshop documentation
Adobe Photoshop File Format Family · Library of Congress — Sustainability of Digital Formats registry
PRONOM fmt/996: Photoshop Large Document · The National Archives (UK) — PRONOM format registry