What is it?
Dithering is a method of showing an image in more colors than are available
to a computer due to hardware or software limitations. Because many
applications (including most web browsers) dither by default, it is very
difficult to actually show pictures of the effect.
How can you display more colors with dithering?
When you use this effect, you are not actually displaying more colors. Luckily,
the human eye can be tricked into seeing colors which are not truly present.
Look at the following image:
If you look closely, you will see red and blue squares in a checkerboard
formation. Stand back a few feet, though, and it looks like purple. You've just
seen a third "color." To get a different shade of purple, it is simply
a matter of changing the pattern to include more red or more blue pixels.
This trick is often used in web browsers to make 256 colors look like
thousands of colors. That is the reason that we made the squares as large
as we did; otherwise, your browser might have dithered the image and the
individual squares might not have been visible.
Dithering generally does very well, which is why it is used so commonly.
The only problem is that the "colors" do not stand up to close scrutiny,
making it a bad choice for viewing high resolution images. As the number
of available colors increases, however it becomes less necessary, and it
is not necessary at all when using millions of colors (24-bit color).
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