Here's a simple test to see if you can get better photos and web graphics by upgrading your monitor or changing its color mode. The differences we show here are subtle, so put on your glasses (if necessary) and look carefully!
Each of the rectangles below is a transition from a darker purple on the left to a slightly ligher purple on the right. Look at the transition zone in the middle of each bar. Which one has a transition zone composed of dot patterns (rather than a smooth gradation)? Click on your answer below.
The one on the left has more dot patterns.
The one on the right has more dot patterns.
In order to represent a photo, your computer monitor breaks the picture up into tiny dots called pixels. It stores a number representing the color of each pixel in 1, 2, or 3 bytes of memory (video RAM). The color depth of a monitor describes how many bytes of memory your monitor uses for each pixel, as expressed in bits (with 8 bits per byte).
16- and 24-bit monitors can be set to display smaller numbers of colors, if desired. If your monitor, at the moment, is only displaying 256 colors, then the color gradients below should look identical. If it is displaying thousands or more colors, the gradient on the right should look very smooth, whereas the one on the left will show speckled patterns. In both cases, you may see some banding, but if so, the bands on the right will each consist of a uniform color, whereas the bands on the left will be specked. The speckled patterns are called dithering.
You responded:
The picture on the right has more dot
patterns than the one on the left.
You are crazy, or something is wrong with your monitor. You may wish to upgrade your monitor and/or computer. See explanation above.
You responded:
The pictures are equally dotty.
Your monitor is only displaying 256 different colors. The left-hand picture is a 256-color version of the thousands-of-colors picture on the right. If you can't see any difference, then the right-hand picture has been reduced to the same 256 colors that the left-hand picture is already using. You may wish to upgrade your monitor and/or computer. See explanation above.
You responded:
The picture on the left has more dot
patterns than the one on the right.
Your monitor correctly displays the subtle but real differences between 256-color graphics and thousands-of-colors graphics. There is no need to adjust or replace it. See explanation above.
Most Macintoshes and Unix computers have monitors which can display
thousands or millions of colors. Many PC-compatible monitors can
only display 256
colors. Moreover, only 216 of the usual 256 colors are specified in
the same way for Macs and PCs.
Accordingly, many web pages which look good on Mac or Unix machines look terrible on PCs.
When a monitor is displaying 256 colors (either because it cannot display more or because it has been set to that value by the system software)--or is asked to display a color other than the 216 which are the same on each brand--the system software approximates the correct color by dithering. It mixes two nearby colors in proportions which mimic the color(s) it cannot perfectly display. This results in more blotches and sometimes a polka-dot pattern.
The image on the right above is a thousands-of-colors JPEG-compressed picture. This looks somewhat better, with smoother colors, on a monitor which can diplay thousands of colors or more. The image on the left is a 216-color GIF picture. It should display the same way on Macs and PCs, but it is just a little bit more blotchy than the JPEG picture.
If you cannot see even a subtle difference between the two pictures, or if you think the one on the right is more blotchy than the one on the left, then your monitor is probably set to 256 colors. You may wish to upgrade to a better monitor (or a better computer, ahem!) to get the finer quality graphics that many web page designers are sending you via their web pages.
This concludes the color-depth test of your monitor. Now go back to
work!
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