Raw bitmap

Revision as of 20:18, 22 June 2014

By a raw bitmap image format, we refer to the loosely-defined class of raster image formats in which the file contains only a list of pixel colors, and nothing else.

Raw bitmap formats are generally not portable, and are best used for temporary files. There is no algorithm to decode an arbitrary unknown raw bitmap image file, but a human expert can usually do so, given enough effort.

Disambiguation

This type of "raw" format is not related to the digital negative formats used by many digital cameras. There, the word "raw" refers to the fact that the image has not been post-processed, not to the structure of the file.

Discussion

The scope of "raw bitmap" formats cannot be precisely defined, but typical characteristics are:

• No header or footer
• Uncompressed
• Does not use a color palette
• Cannot be decoded without external information, such as:
  • Color type and sample order (RGB, BGR, grayscale, etc.)
  • Image width in pixels
  • Row padding logic
  • Byte order and/or bit order

Some image editors are capable of importing (some) raw bitmap formats, after prompting the user for information about the image's dimensions, color format, etc.

Some image formats are structured as raw bitmaps, but can still be reliably decoded just by knowing the name of the format, because all images in that format have the same attributes. Examples of this are Sony Mavica 411, PGF (Portfolio Graphics), and many other formats associated with early home computers (which often use a standard color palette). Whether such formats should be counted as "raw bitmap" formats is a matter of opinion.

Some articles dealing with various sorts of raw bitmaps (perhaps along with images of other sorts) include:

• Apple II graphics formats
• Atari graphics formats
• BSAVE Image