.PSD

Adobe Photoshop Document

Introduction

PSD is the native file format of Adobe Photoshop. It keeps a whole working document: every layer with its blend mode and opacity, masks, adjustment layers, text, paths, guides and colour profiles, as well as a flattened copy of the finished image.

Adobe publishes a specification of the format. Documents larger than 30,000 pixels on a side or 2 GB in size use the Large Document Format, PSB, which has the same layout with wider length fields. Many other editors read PSD, though each supports a different share of Photoshop’s features.

Software

Structure

A PSD file has five sections in a fixed order, and all numbers are big-endian. The 26-byte header starts with 8BPS and gives the version (1 for PSD, 2 for PSB), the number of channels, the height and width, the bits per channel and the colour mode. Each later section starts with its own length, so a reader can skip what it does not need.

  1. 0File header 8BPS, version, channels, size, depth, colour mode26 bytes
  2. 26Colour mode data the palette of an indexed image, otherwise empty4 bytes and up
  3. …Image resources 8BIM blocks: resolution, guides, thumbnail, profilevaries
  4. …Layer and mask information each layer’s bounds, blend mode, masks and pixel channelsvaries
  5. …Image data the flattened composite, raw or compressedvaries
A PSD file: five sections in a fixed order