PSB File (.psb): What It Is and How to Open It

The basics

What is a PSB file?

PSB is Photoshop's Large Document Format. It holds exactly what a PSD holds, layers, masks, text, smart objects, adjustment layers, channels and paths, but without PSD's size limits. Adobe added it in Photoshop CS in 2003, when PSD's 30,000-pixel and 2 GB limits started getting in the way.

You'll meet PSB files wherever images get very large: stitched panoramas and gigapixel photos, billboard and large-format print artwork at full resolution, scanned maps and artworks, film matte paintings, and layered documents with many big smart objects. Photoshop won't save a document as PSD once it passes those limits, so PSB is the way out.

It isn't a different kind of image. A PSB is the PSD format with some length fields made wider. A small image saved as PSB is still a valid PSB.
Few apps outside Adobe read it. Many programs that open PSD files reject PSB, or crash on large ones.
Browsers can't display it. A link to a PSB downloads the file.

Anatomy

What's inside a PSB file

A PSB has the same five parts as a PSD, in the same order: a 26-byte header, then four sections that each start with their length. There's no sample on this page, so to show real bytes we wrote a small two-layer PSB with ImageMagick and walked through it. Photoshop's files contain far more image resources and layer data, but the layout is the same. All numbers are big-endian; look for the length fields that are 8 bytes instead of 4.

big.psb (header in hex, then the structure)

38 42 50 53   00 02   00 00 00 00 00 00
00 03   00 00 01 90   00 00 02 80   00 08   00 03

00 00 00 00                 colour mode data: 0 bytes
00 00 00 00                 image resources: 0 bytes

00 00 00 00 00 0C A3 12     layer and mask info: 828,178 bytes
  00 00 00 00 00 0C A3 06   layer info: 828,166 bytes
  00 02                     2 layers, bottom to top:
  [0] Sky   0,0 to 400,640    3 channels:
        00 00  00 00 00 00 00 03 E8 02   red: 256,002 bytes
        00 01  00 00 00 00 00 03 E8 02   green
        00 02  00 00 00 00 00 03 E8 02   blue
  [1] Sun   50,400 to 150,600  3 channels:
        00 00  00 00 00 00 00 00 4E 22   red: 20,002 bytes
        …
  channel image data for both layers (raw)

00 01                       image data: the composite, RLE
  00 00 00 0D  00 00 00 0D …   1,200 row lengths, 4 bytes each
  …                            (2 bytes each in a PSD)
                            21,002 bytes; file total 849,222

138 42 50 53 00 02
Signature and version
8BPS, as in every Photoshop file, then version 2. A PSD has version 1 here. This is the only reliable way to tell the two apart, and the reason a PSB renamed to .psd still won't open in apps that only read PSD.
200 03 00 00 01 90 00 00 02 80
Channels, height, width
3 channels, 400 pixels high, 640 wide. Height and width are 4-byte fields in both formats; Adobe's specification allows up to 30,000 in a PSD and 300,000 in a PSB.
300 08 00 03
Bit depth and colour mode
8 bits per channel, colour mode 3 (RGB). The same values as in a PSD: 1, 8, 16 or 32 bits, and bitmap, greyscale, indexed, RGB, CMYK, multichannel, duotone or Lab.
400 00 00 00 00 00 00 00
Colour mode data and image resources
Both empty here and both unchanged from PSD, with 4-byte lengths. Photoshop puts resolution, thumbnail, metadata, guides and paths in the image resources.
500 00 00 00 00 0C A3 12
An 8-byte section length
The length of the layer and mask section. In a PSD it's 4 bytes, which can't count past 4 GB; a PSB widens it to 8. The layer info length inside it is widened the same way.
600 00 00 00 00 00 00 03 E8 02
Channel records
Each layer lists its channels: a 2-byte channel ID (0 red, 1 green, 2 blue, -1 transparency), then the length of that channel's data, also 8 bytes in a PSB. 256,002 is a 2-byte compression code plus 640 × 400 uncompressed bytes.
700 01
The composite image
The flattened picture, compressed with RLE (code 1). It's what most other apps show, as in a PSD; Photoshop writes it when Maximize Compatibility is on.
800 00 00 0D
RLE row lengths
Before RLE data comes the compressed length of every row of every channel: 400 rows × 3 channels = 1,200 values. A PSB stores each in 4 bytes, a PSD in 2. A reader that assumes PSD here reads garbage.

Comparison

PSB vs PSD: what's different

	PSD	PSB
Extension	`.psd`	`.psb`
Header version	1	2
Maximum width and height	30,000 pixels	300,000 pixels
Maximum file size	2 GB	Up to 4 exabytes
Layer and mask section length	4 bytes	8 bytes
Channel data lengths	4 bytes	8 bytes
RLE row lengths	2 bytes	4 bytes
Some tagged layer blocks (16- and 32-bit layers, filter masks, linked smart object files…)	4-byte length	8-byte length
Opened by	Most image editors and many viewers	Photoshop and a handful of others

Everything else, the 26-byte header layout, the colour modes and bit depths, image resources, blend modes, compression methods and the composite image, is the same. A program that already reads PSD properly needs only a few changes to read PSB, which is why the list of programs that support it is short but growing.

Why not always use PSB?

There's no quality difference, but PSD opens in far more programs, previews and online services. Save as PSD whenever the document fits, and only use PSB when Photoshop says it doesn't.

Sizes

How big is too big for a PSD?

Two limits push a document into PSB: 30,000 pixels in width or height, and 2 GB of file. The pixel limit is easy to picture as a print size:

Print resolution	30,000 pixels (PSD limit)	300,000 pixels (PSB limit)
300 ppi (photo print)	100 inches, 2.54 m	1,000 inches, 25.4 m
150 ppi (poster)	200 inches, 5.08 m	2,000 inches, 50.8 m
72 ppi (large banner)	About 417 inches, 10.6 m	About 4,167 inches, 106 m

The file-size limit is often reached before the pixel limit. One 8-bit RGB layer of 30,000 × 30,000 pixels is 2.7 GB before compression, and every extra layer, 16-bit mode, extra channel or embedded smart object adds more. Stitched panoramas, multi-layer composites for large-format print and scans of large originals are the usual cases.

Before switching to PSB, check whether you need all that data: a huge layered file can often be split into parts, flattened where layers are final, or reduced to the resolution the output actually needs.

How to

How to open and convert a PSB file

Photoshop (CS and later) opens and saves PSB on Windows and macOS. Choose File, Save As, Large Document Format.
Affinity Photo opens PSB files but can't save them.
Krita (free) can load PSB files; it doesn't save them.
ImageMagick reads and writes PSB: magick 'big.psb[0]' big.tif converts the composite. The psd-tools Python library reads PSB too. Pillow, the Python imaging library, doesn't recognise PSB at all.
Just to look at it: many previewers that show PSD files skip PSB. Ask for a JPG or PNG export, or a smaller PSD.

Turning a PSB into something easier to share
You want	Do this in Photoshop
A smaller layered file	Image, Image Size to bring it under 30,000 pixels, flatten or delete unused layers, then save as PSD
One flat image	File, Export, Export As PNG or JPEG, at a size the recipient can use; JPEG itself is limited to 65,535 pixels on a side
A big flat image for print	Save a flattened TIFF; classic TIFF stops at 4 GB, BigTIFF goes further
Layers for another app	Export the layers you need as separate files

Troubleshooting

Common PSB problems

Photoshop won't save a PSD. The document is over 30,000 pixels on a side or would be over 2 GB. Save it as Large Document Format (PSB) instead, or reduce it.
An app says the file is invalid or unsupported. It reads PSD but not PSB. Check the first six bytes: 38 42 50 53 00 02 is a PSB, whatever the extension says. Renaming it to .psd doesn't help.
Thumbnails are missing. Many operating system previewers and cloud storage services don't generate previews for PSB. The file is usually fine.
The file is enormous and slow. PSB files are big by nature: a 100,000 × 50,000-pixel RGB image is 15 GB of pixels per layer before compression. Work on a fast local drive with plenty of free space for Photoshop's scratch disk, not on a network or synced folder.
The upload is rejected or served with a strange type. Some servers' MIME tables (Debian's, for one) map .psb to application/vnd.3gpp.pic-bw-small, an unrelated mobile-phone image type. Send image/vnd.adobe.photoshop or application/octet-stream instead.

Security

Privacy and security

A PSB can hold everything a PSD can: hidden layers, pixels outside the canvas, earlier versions inside smart objects, and metadata such as author names and the GPS location of placed photos. Check the Layers panel and File Info before sending one, or send a flattened export.

A PSB can't run code. For servers, the risk is size: the header can declare a 300,000 × 300,000-pixel image, which would need hundreds of gigabytes of memory to decode. Check the declared width, height, channels and bit depth before decoding an uploaded PSB or PSD, and set memory limits in image libraries such as ImageMagick's policy.xml.

Sample files

There are no sample PSB files on this page yet. To make one for testing, save any image from Photoshop with File › Save As › Large Document Format, or convert one with ImageMagick: convert image.png image.psb. For layered test files in the smaller format, see our PSD samples.

Put it online

Have a PSB file? Give it a link.

Drop a PSB on 99helpers and it gets its own link. Browsers can't display PSB files, so anyone who opens the link downloads it for Photoshop or another editor; add a JPG or PNG preview next to it so people can see the image first.

Put a PSB file online

Questions

PSB files, frequently asked

What is a PSB file?

A Photoshop document in the Large Document Format: the same as a PSD, but for images over 30,000 pixels on a side or files over 2 GB. It supports up to 300,000 × 300,000 pixels.

What's the difference between PSB and PSD?

PSB has version 2 in its header instead of 1, and some length fields are 8 bytes instead of 4, so it can hold far larger images and files. Everything else is the same, but far fewer apps open PSB.

How do I open a PSB file without Photoshop?

Affinity Photo and Krita can open PSB files, and ImageMagick can convert them on the command line. Many apps that open PSD don't support PSB.

Can I rename a PSB to PSD?

No. The header and several length fields differ, so a PSD reader can't read it. Open it in Photoshop and save it as PSD, after reducing it below 30,000 pixels and 2 GB if needed.

When should I save as PSB?

Only when a document is too big for PSD, over 30,000 pixels in width or height or over 2 GB. Photoshop will tell you. Otherwise PSD is more widely supported.

How do I convert a PSB to JPG or PNG?

In Photoshop, use File, Export, Export As, reducing the size if needed: JPEG is limited to 65,535 pixels on a side. With ImageMagick, magick 'file.psb[0]' file.png converts the flattened image.

Can a browser open a PSB file?

No. A link to a PSB downloads it. Export a JPG or PNG to show the image on a web page.

Related formats

Other file types explained

PSD file TIFF file PNG file JPEG file XCF file AI file All file types

Keep going

Host a PSB file

Put a large Photoshop document online at its own address.

Share a PSB file

Send a PSB as a link instead of an attachment.

Sources

Last reviewed 27 October 2026.