Balloon and Tower Images
Images with no single primary color
Or the "mandatory balloon picture". While the human eye can see over 2 million different colors it is very rare to find any single image with over 80,000 unique colors. Many images can be reduced to only 256 colors as in the Niagara falls example. Normally images with one primary color are reduce the best. The classic example of a picture that does NOT reduce well would be a picture of hot air balloons. Normally theses pictures have many different colors. The more primary colors in an image the fewer shades of each color you get. This causes the effect of "color banding" as shown below. Look at the balloon on the left and notice how the red and orange colors do not smoothly change.
Balloon picture by "Andy Steere".
Color Banding
The niagra tower image below is an image with a good natural sky color. A blue sky is not a single color but has a very gradual gradient of blue color. Because of this, the sky is normall the first place you will see color banding problems in an image that has been color reduced.
Things of Note About This Image.
This image looks quite good as a 256 color image. Most images with a good blue sky do not. This is probably because this image has almost no secondary colors, as can be seen in the color palette.
Also of notice is the file size of the JPG and the GIF images. Notice that the GIF image is larger than the JPG. This is unusual, but common enough such that questions like "which file format is smaller" can only be answered in general terms.
Dither
Dithering is a process used in the printing of black and white images for newspapers. A standard printing press can only print black or white. To get gray you print alternating black and white dots very close togeather. At a distance the human eye sees this as gray. Photoshop has an algorythm to ajust pictures to dither. This is not built into the GIF file format but a filter applied to an image that can then be saved any way you want.
Below are two images one dithered, one using the pattern method of dithering before saving.
Under that is a zoomed in section of the sky.
Next -----> Random Examples
Images with no single primary color
Or the "mandatory balloon picture". While the human eye can see over 2 million different colors it is very rare to find any single image with over 80,000 unique colors. Many images can be reduced to only 256 colors as in the Niagara falls example. Normally images with one primary color are reduce the best. The classic example of a picture that does NOT reduce well would be a picture of hot air balloons. Normally theses pictures have many different colors. The more primary colors in an image the fewer shades of each color you get. This causes the effect of "color banding" as shown below. Look at the balloon on the left and notice how the red and orange colors do not smoothly change.
 46,630 unique colors JPEG Format 57 k |
 256 unique colors GIF Format 42 k |
Balloon picture by "Andy Steere".
Color Banding
The niagra tower image below is an image with a good natural sky color. A blue sky is not a single color but has a very gradual gradient of blue color. Because of this, the sky is normall the first place you will see color banding problems in an image that has been color reduced.
 9,959 unique colors JPEG Format 22 k |
 256 unique colors GIF Format 44 k |
|
256 unique colors |
 |
 32 unique colors |
 |
Things of Note About This Image.
This image looks quite good as a 256 color image. Most images with a good blue sky do not. This is probably because this image has almost no secondary colors, as can be seen in the color palette.
Also of notice is the file size of the JPG and the GIF images. Notice that the GIF image is larger than the JPG. This is unusual, but common enough such that questions like "which file format is smaller" can only be answered in general terms.
Dither
Dithering is a process used in the printing of black and white images for newspapers. A standard printing press can only print black or white. To get gray you print alternating black and white dots very close togeather. At a distance the human eye sees this as gray. Photoshop has an algorythm to ajust pictures to dither. This is not built into the GIF file format but a filter applied to an image that can then be saved any way you want.
Below are two images one dithered, one using the pattern method of dithering before saving.
Under that is a zoomed in section of the sky.
|
32 colors No Dither |
 32 colors Pattern Dither |
 Zoom No Dither |
 Zoom Pattern Dither |
Next -----> Random Examples