What Is PSD?
PSD stands for Photoshop Document, Adobe Photoshop's native file format, introduced with the first version of Photoshop in 1988. PSD is a proprietary binary format that stores the full editing state of a Photoshop document: all layers, masks, adjustment layers, smart objects, channels, guides, slices, paths, and other non-destructive editing information.
PSD is the working format of graphic designers, photographers, digital artists, and web designers using Photoshop. Unlike flattened formats like JPEG or PNG that discard layer information, PSD preserves every editing decision in a non-destructive, re-editable state.
A related format, PSB (Photoshop Big), uses the same structure but supports files larger than 2 GB (up to 300,000 × 300,000 pixels), making it the format of choice for large-format printing, panoramas, and billboard-scale composites.
File Size Limit: PSD vs. PSB
| Format | Max file size | Max dimensions | Notes |
|---|---|---|---|
| PSD | 2 GB | 30,000 × 30,000 px | Standard Photoshop |
| PSB | 4 EB (theoretical) | 300,000 × 300,000 px | "Large Document Format" |
Most workflows stay within PSD limits. PSB is required for ultra-high-resolution work (20+ megapixel panoramas, billboard printing at 300 DPI).
PSD Internal Structure
PSD files are organised into five sections:
1. File Header (26 bytes):
- Signature:
8BPS - Version: 1 (PSD) or 2 (PSB)
- Channel count (1-56)
- Image height, width
- Bit depth (1, 8, 16, 32 bits per channel)
- Colour mode (Bitmap, Grayscale, Indexed, RGB, CMYK, Multichannel, Duotone, Lab)
2. Colour Mode Data (variable):
- For indexed colour: the colour table (768 bytes)
- For duotone: the duotone specification
- Empty for other modes
3. Image Resources (variable):
- Non-pixel metadata: ICC profile, guides, slices, history states, document-level annotations, print settings, web output settings, paths
- Each resource identified by a 4-byte ID code
4. Layer and Mask Information (the large section):
- Layer count
- For each layer:
- Bounding rectangle
- Channel data offsets/lengths
- Blend mode (NORM=Normal, MUL=Multiply, SCRN=Screen, OVRL=Overlay, etc.)
- Opacity (0-255)
- Layer flags (visibility, pixel lock, etc.)
- Layer name
- Additional layer info (adjustment type, smart object link, type layer font/text, effects, vector mask, etc.)
- Global layer mask info
- Tagged blocks of additional layer data
5. Image Data (the merged/flattened composite):
- The final composited image (all layers merged)
- This allows applications that don't understand layers to display the file as a flat image
- Compression: Raw, RLE (PackBits), ZIP without prediction, ZIP with prediction
Layer Types
PSD supports many layer types, all stored in the Layer and Mask Information section:
Pixel layers — ordinary painted/photo layers with raster content.
Adjustment layers — non-destructive modifications that affect layers below:
- Brightness/Contrast, Levels, Curves, Exposure
- Hue/Saturation, Color Balance, Black & White, Photo Filter
- Channel Mixer, Color Lookup, Invert, Posterize, Threshold
- Gradient Map, Selective Color
- Vibrance
Type layers — vector text that remains editable (font, size, tracking, kerning stored as metadata, not pixels).
Shape layers — vector paths with fill and stroke; scales without quality loss.
Smart Objects — encapsulated files (raster images, vector files, other PSDs) that preserve original data and support non-destructive transformations. All scale operations on a smart object operate on the original, not the currently sized version.
Fill layers — solid color, gradient, or pattern fills.
Group layers — folders containing other layers with their own blend mode and opacity.
3D layers — Adobe Dimension or older 3D engine objects (increasingly deprecated).
Video layers — for video editing in Photoshop (PSD can contain video timeline data).
Blend Modes
Photoshop implements 27 blend modes, stored as 4-character codes in the PSD:
| Code | Mode | Mathematical operation |
|---|---|---|
| NORM | Normal | B = top layer |
| DISS | Dissolve | Random pixel selection based on opacity |
| DARK | Darken | min(A, B) |
| MUL | Multiply | A × B / 255 |
| IDIV | Color Burn | Darkens bottom by reflecting top |
| LDDG | Linear Burn | A + B - 255 |
| LITE | Lighten | max(A, B) |
| SCRN | Screen | 255 - (255-A) × (255-B) / 255 |
| DIV | Color Dodge | Brightens bottom to reflect top |
| LGDS | Linear Dodge | A + B |
| OVRL | Overlay | Screen or Multiply based on base |
| SLIT | Soft Light | Similar to Overlay, gentler |
| HLIT | Hard Light | Strong Overlay |
| VLIT | Vivid Light | Combination burn/dodge |
| LLIT | Linear Light | Linear burn/dodge |
| PLIT | Pin Light | Darken or Lighten based on blend |
| HMIX | Hard Mix | Posterised overlay |
| DIFF | Difference | |
| SMUD | Exclusion | A + B - 2AB / 255 |
| FSUB | Subtract | A - B |
| FDIV | Divide | A / B |
| HUE | Hue | Hue of top, saturation+luminance of bottom |
| SAT | Saturation | Saturation of top, hue+luminance of bottom |
| COLR | Color | Hue+saturation of top, luminance of bottom |
| LUM | Luminosity | Luminance of top, hue+saturation of bottom |
PSD vs. TIFF vs. PDF vs. PNG
| Feature | PSD | TIFF | PNG | |
|---|---|---|---|---|
| Layers | Yes (full) | No (standard) | No (appearance only) | No |
| Adjustment layers | Yes | No | No | No |
| Smart objects | Yes | No | No | No |
| Vector masks | Yes | No | Yes (vector only) | No |
| Max bit depth | 32-bit float | 32-bit float | Any | 16-bit int |
| CMYK | Yes | Yes | Yes | No |
| ICC profiles | Yes | Yes | Yes | Yes |
| Universal compatibility | Low | High | Very high | Very high |
| File size | Large | Large | Medium | Medium |
| Lossless | Yes | Yes | Depends | Yes |
Compatibility
PSD files can be opened by:
- Adobe Photoshop — full native support, all features
- Adobe Illustrator — places PSD as smart object, limited layer editing
- Adobe After Effects — imports PSD with layers as composition
- GIMP — good PSD support; most layer types; some advanced features limited
- Affinity Photo — excellent PSD compatibility, including adjustment layers
- Pixelmator Pro (macOS) — good compatibility
- Canva, Figma — partial; typically renders flat or basic layers only
- Procreate — imports PSD with layers (iPad)
- Apple Preview — displays flattened composite only
Converting PSD
PSD → JPEG/PNG: File → Export → Quick Export as PNG/JPEG (Photoshop) or flatten layers first → Save As. Merges all layers into a flat image.
PSD → TIFF: File → Save As → TIFF. TIFF preserves 16-bit depth and ICC profiles; layers are merged. Use for archival or print delivery.
PSD → PDF: File → Save As → Photoshop PDF. Can embed ICC profile, preserve vector elements, compress images. PDF/X-4 is the standard for print-ready delivery.
PSD → WebP: Via Quick Export in newer Photoshop versions, or export JPEG/PNG → convert to WebP.
PSD → Multiple assets: File → Export → Export As (or Generate via document settings) for extracting individual layers as separate files.
Summary
PSD is the definitive working format for professional image editing in Photoshop. Its layer system — pixel layers, adjustment layers, smart objects, masks, blend modes, and type layers — enables complex non-destructive workflows where every editing decision remains reversible. Its proprietary nature limits compatibility to Adobe products and select third-party applications, making it a format to stay in during production and export from for delivery. PSB extends PSD's capabilities to ultra-large documents. For final delivery to clients, printers, or web platforms, always export from PSD to an appropriate distribution format (JPEG, PNG, TIFF, or PDF).
Related conversions
Most teams that read this guide convert images in one of these directions: