Raw bitmap

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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.
 
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.
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Raw bitmap formats are generally not portable, and are best used for temporary files. There is no algorithm to decode an arbitrary raw bitmap image file, but a human expert can often do so, given enough effort.
  
 
== Disambiguation ==
 
== Disambiguation ==
This type of "raw" format is not related to the [[Cameras and Digital Image Sensors|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.
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This type of "raw" format is not related to the [[Cameras and Digital Image Sensors|digital negative formats]] used by many digital cameras. There, the word "raw" refers to the fact that the image has not been post-processed, and does not refer to the structure of the file.
  
== Discussion ==
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== Details ==
The scope of "raw bitmap" formats cannot be precisely defined, but typical characteristics are:
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The scope of "raw bitmap" formats cannot be precisely defined, but typical characteristics include:
 
* No header or footer
 
* No header or footer
 
* Uncompressed
 
* Uncompressed
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** [[Endianness|Byte order]] and/or [[bit order]]
 
** [[Endianness|Byte order]] and/or [[bit order]]
  
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== Variations ==
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It is a matter of opinion whether the types of formats described in the section should be considered to be raw bitmap formats.
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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 include [[Sony Mavica 411]] and [[PGF (Portfolio Graphics)]].
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 +
Many older formats, especially those associated with home computer systems, are (more or less) just a dump of the computer's video memory. They often use a standard color palette, and ''can'' be reliably decoded if you know the name of the format. The pixels and/or the bits corresponding to a particular pixel are often arranged in (what today seems like) an unusual order. Examples include many [[Apple II graphics formats]] and [[Atari graphics formats]].
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 +
Some formats do have a header, but it is insufficient to reliably decode the image. The PC variant of [[BSAVE Image]] is an example.
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Some formats contain only one ''plane'' of an image, e.g. only the red samples.
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== Software ==
 
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 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.
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* [[ImageMagick]]
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** Formats named CMYK, CMYKA, GRAY, MONO, PAL, RGB, RGBA, RGBO, UYVY, YCbCr, YCbCrA, YUV (complete image)
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** Formats named A, B, C, G, K, M, O, R, Y (single sample)
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* [[Farbfeld Utilities]]
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** <code>rgbff</code> - RGB/RGBA, in various orders and padding, planar, premultiplied-alpha, etc
 +
** <code>bitff</code> - Indexed colour images, with 1, 2, 4, or 8 bits per pixel, various kinds of bit orders and packing

Revision as of 16:48, 10 November 2017

File Format
Name Raw bitmap
Ontology
Extension(s) .raw, .rgb, .yuv, many others
PRONOM x-fmt/185 (?)

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 raw bitmap image file, but a human expert can often do so, given enough effort.

Contents

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, and does not refer to the structure of the file.

Details

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

  • 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

Variations

It is a matter of opinion whether the types of formats described in the section should be considered to be raw bitmap formats.

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 include Sony Mavica 411 and PGF (Portfolio Graphics).

Many older formats, especially those associated with home computer systems, are (more or less) just a dump of the computer's video memory. They often use a standard color palette, and can be reliably decoded if you know the name of the format. The pixels and/or the bits corresponding to a particular pixel are often arranged in (what today seems like) an unusual order. Examples include many Apple II graphics formats and Atari graphics formats.

Some formats do have a header, but it is insufficient to reliably decode the image. The PC variant of BSAVE Image is an example.

Some formats contain only one plane of an image, e.g. only the red samples.

Software

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.

  • ImageMagick
    • Formats named CMYK, CMYKA, GRAY, MONO, PAL, RGB, RGBA, RGBO, UYVY, YCbCr, YCbCrA, YUV (complete image)
    • Formats named A, B, C, G, K, M, O, R, Y (single sample)
  • Farbfeld Utilities
    • rgbff - RGB/RGBA, in various orders and padding, planar, premultiplied-alpha, etc
    • bitff - Indexed colour images, with 1, 2, 4, or 8 bits per pixel, various kinds of bit orders and packing
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