Dithering

• If the bitmap (or bitmapped device) only allows black and white, dithering can be used to produce an illusion of gray.
  
  
• If the bitmap (or bitmapped device) allows a palette of colors, then dithering can produce an illusion of more colors being displayed than are in the palette.

Zoomed In 25% Black, 75% White		Actual Size Dithered Image

Zoomed In 50% Black, 50% White		Actual Size Dithered Image

Zoomed In 75% Black, 25% White		Actual Size Dithered Image

Zoomed In 50% Red, 50% Yellow		Actual Size Dithered Image

1. Some methods of dithering can produce the illusion of patterns within the colored areas. This can be a significant problem when dithering images containing naturalistic images (for example, photographs), and tends to be particularly noticeable when dithering is used on relatively low resolution devices.
   
   
2. Various methods of dithering have been devised (some of which may produce less obvious patterning than others). These include:
   
   
   • Average Dithering
     
     
   • Floyd-Steinberg Dithering
     
     
   • Ordered Dithering (a common variant of which is Bayer Dithering).
     
     
   • Random Dithering
   
   
3. Once an image has been dithered, it can be extremely hard to edit.
   
   For example, if we had an image which contained areas that had been dithered (like the examples above) to produce orange and various shades of gray, there is no simple way to adjust the color of those areas, because each area contains a mix of pixels of different colors.
   
   As a result, in an ideal world, images would be prepared and stored in full color, and then only dithered when displayed/printed on a device which did not support all the necessary colors. However, in the real world, the limitations of networks, storage, memory, and graphics file formats, frequently means that despite this significant disadvantage, images are often prepared and stored already dithered.
   
   
4. Dithered images contain lots of fine detail that may not compress well, particularly in file formats that use LZW or Run-length Compression.
   
   As a result, in some cases, it may actually take less storage and bandwidth to store and transmit images in full TrueColor, and allow the output device to perform any necessary dithering upon receiving this image. An example where this may occur is if web publishing images in PNG format.
   
   Related Pages on this site:
   • Average Dithering (Definition)
     
     
   • Bayer Dithering (Definition)
     
     
   • Floyd-Steinberg Dithering (Definition)
     
     
   • Ordered Dithering (Definition)
     
     
   • Random Dithering (Definition)
   
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