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GFF's Guide to Saving Pictures for the Web
Final compression and using the right format can be as important as taking good photos and scanning them correctly.
There are basically two formats, which are useful for the web: GIF and JPEG. A rule of thumb is JPEG for photos, GIF for graphics and logos. None of these are particularly good for storing the originals, as they both manipulate the picture with a potential loss of quality, but each has advantages in making small files, which load fast and work in a manner suitable for web use.
JPEG is the one that can make the smallest files, but also the one that can do most damage. The JPEG format can be compressed in different degrees, and if you use too high a compression factor, you will wind up with a very poor picture. JPEG alters the picture and will leave obvious, visible traces in the picture. On the other hand JPEG-compression can do wonders to file size with almost no trace of compression.
The danger of JPEG lies in large areas of almost uniform colors, which can get a strange box-like structure when compressed too hard. A discrete blue background is a good example of such a fragile element. Pictures with more details, hackles, feathers, dubbing, mixed colors will render well with JPEG-compression.
GIF works in a different manner. GIF does not alter the picture as such, only the colors. The maximum number of colors in a GIF picture is 256 - in some cases 216 as we will see later. These colors can be selected from an almost endless scale, but you can only use a limited number. GIF works its magic by this limitation and compressing the picture in a way that does not deteriorate it.
As mentioned GIF works partly by limiting the colors. The color collection used is called a palette. The palette is limited to 256 colors, but by further reducing the number of colors you can compress the picture significantly. Naturally a picture with 64 or even 32 hues has a less chance of representing the content properly, but it is absolutely worth looking into the GIF as an alternative to JPEG.
If you want to make GIF's which come out as good as possible on all systems, you have to fall back to the so called browser safe palette of 216 specific colors. By doing this you severely lessen your chances of showing a perfect picture, but you do enhance your chances of having the picture shown on the user's screen the same way as it is shown on yours. JPEG will do the same, though.
GIF is undoubtedly the best format for logos and graphics, which contain areas of uniform colors, but for fly pictures it is not the greatest file format.
Both GIF and JPEG can be interlaced. Interlacing is a technique by which the picture can be shown in stages - typically three or four - with increasing quality.
When the picture loads, it is shown in a rough version at first, and through a few iterations, it is completed to its full quality.
The purpose of this is to give the user a chance of judging the picture before it is fully loaded. This is no longer as needed as it was in the prehistoric Internet age, but for large pictures it can still be convenient. When you interlace a picture it can sometimes grow a bit.
Save your work
When you are satisfied with the result it is time to save your work. This stage is the refined stage, where the picture is in its optimal quality regarding web use. It is not suitable for anything else than putting on a web site. If you want to store it for future use, work on it again or print it, return to the last saved TIFF-file, where the optimum quality can be found, or work from the original, where all the picture's original details are present.