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. 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.
   
   There are various methods of dithering available - and which is best in each case depends on the content of image, and of course, personal taste.
   
   Shown below is a color image that has been converted to monochrome using some different dithering methods:
   
   

   Original Image:

   Ordered Dithering: Jarvis Dithering:

   Floyd-Steinberg Dithering: Stucki Dithering:

   
   Next, we compare reducing the color depth of an image using different approaches. Shown below is a color image that has been converted from True Color to the greatly reduced color depth of color-safe palette using three different methods: no dithering, Ordered Dithering, and Floyd-Steinberg Dithering.
   
   

   Color-Safe (No dithering):

   Color-Safe (Ordered Dithering): Color-Safe (Jarvis Dithering):

   Color-Safe (Floyd-Steinberg Dithering): Color-Safe (Stucki Dithering):

   
   
2. 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.
   
   
3. 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 True Color, 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 the PNG file format.

• Average Dithering (also known as "Thresholding")
  
  
• Ordered Dithering (a common variant of which is Bayer Dithering).
  
  
• Random Dithering
  
  
• Floyd-Steinberg Dithering
  
  
• Jarvis, Judice & Ninke Dithering (often known as "Jarvis Dithering")
  
  
• Stucki Dithering

• Average Dithering (Definition)
  
  
• Bayer Dithering (Definition)
  
  
• Floyd-Steinberg Dithering (Definition)
  
  
• Half-Tone (Definition)
  
  
• Jarvis, Judice & Ninke Dithering (Definition)
  
  
• Ordered Dithering (Definition)
  
  
• Random Dithering (Definition)
  
  
• Stucki Dithering (Definition)