Troubleshooting Photos –
Abrupt Color Changes, No Detail
Problem
The colors are roughly accurate, but instead of gradual changes in color, as for instance between the sunny and dark side of an object like the yellow sailing mark, there are sudden changes from one block of light color to another block of dark color as seem in poster 1. In some cases the transitions may be marked by clearly visible points of different colors, as in poster 2.
What should you look for?
It would be fairly easy to miss the problem with this picture if it were not for the sailing mark (on-screen, anyway – in print, banding like this shouts its presence throughout the photo). Instead of the almost infinite gradation of colors that you'd expect as the sunny yellow side transitions into the shaded side, you have harsh transitions and five big blocks of color with no variation. Once you've been alerted by this giveaway, it's easy to spot the monochrome reds of the forward-facing sailor's life jacket and the blotches of black on the stern of the boat.
Once you know what to look for, you'll notice a fair number of photos like this on the Web, even on large corporate sites where the people should know better.
What should you do?
A photo like this is said to be posterized, because it resembles a silk-screened poster, which is rendered with large blocks of a limited range of colors, and every photo-editing package now available has tools to help you achieve this effect (it has its uses). Did you accidentally use a posterizing filter on the picture? Probably not. Probably, you saved your photo as a GIF, a very old but still useful format that creates small files by ruthlessly limiting the number of colors and the amount of detail in the picture.
poster 1 shows the picture as a 64-color GIF. poster 2 shows the picture as a 64-color dithered GIF. Dithering softens the harsher transitions by blending the same limited set of colors in smaller areas to create the illusion of new colors, much as the French impressionist Seurat did in his pointillist paintings. Look at the natural-color wood in the front of the boat's cockpit – in poster 1, it's big blotches of olive and red masquerading as mahogany; in poster 2, it's smaller points of olive and red masquerading as mahogany. It's a better blend and it's an improvement, but it's not photographic color and of course the detail is limited.
How do you fix it?
Go back to your source, which should be a full-fledged photo format such as JPEG, TIFF or RAW (see this full discussion of photo formats, including appropriate uses for GIF) and re-save the picture as a JPEG or other photo format. Then you'll see smooth color transitions and detail as shown in correct, which brings out the true color and detail. If necessary go back to your original (see the suggestions on creating a safety net for your originals right from the camera in About JPEG).
