Image file formats

Digital image file formats are important to understand.  There are three kinds, classified by their position in the production process:

    • Camera capture formats, such as Camera Raw (non-lossy) or JPG (lossy)
    • Working formats, like Photoshop’s  .psd or Gimp’s  .xcf  — These can’t be opened in any other application  
    • Interchangeable formats
      • Formats for web  –  .gif,  .jpg,   .png, .heic, Google’s webp   (These are compressible, or “lossy”)
      • Lossless formats for printing — pdf and  .tiff

This is a simplified overview of the most significant formats, attributes and  uses.

Name Channels Mode Color depth Suffix Pro / Con  Typical Use
Raw     (camera capture / input)    3  Raw 
  12 or 14 bits  per channel (4096-16384 shades) Depends on camera type. EX: .crw (Canon) Lossless
Retains full gamut before formatting		 Storage in camera NOT FOR WEB
GIMP Experimental computing facility  4 (any) Working format (for GIMP)
 .xcf Lossless NOT FOR WEB 
Photoshop Document  4 (any) Working format (for Adobe Photoshop)
 .psd Non-lossy. No  compression.   NOT FOR WEB 
 Adobe Portable Document Format  N/A  File exchange. format  .pdf   Non-lossy, can be compressed OK for WEB Flat text, graphics,  interactive elements,  rich media
Graphic
Image
Format		 1  Indexed, greyscale  8 bit, only 256 total colors but pallets vary
 .gif no compression, good transparency, animation FOR WEB – Maps, cartoons 
Joint
Photographic
Experts
Group 
 3 RGB 16 million colors
(no transparency)		 .jpg .jpeg
 Good compression  FOR WEB – Complex photos. Best for simple web sites.  
Scalable Vector Graphics  3 RGB 16 million colors 
 .svg
 Scalable without aliasing / Not bitmapped FOR WEB  
Portable
Network
Graphics		 4 RGB 16 million colors plus alpha channel (transparencies).  .png Better compression than jpg,  Best for https   FOR WEB
 High Efficiency Image Container  RGB  16 bit processing, billions of colors .heic  default format for Apple devices  /  from MPEG  FOR WEB (no transparency) 
Tagged Image File Format  CMYK 4 billion possible colors  .pict .tiff  Lossless Limited  compression FOR PRINTING  
Flexible image transport system  4 (any) Scientific and archival format  .fts, .fits Non-lossy; backwards compatible (to 1981). Good photometric notations Working format for FITS Liberator
NOT FOR WEB 

 

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