Image Processing Reference
In-Depth Information
Before we turn our attention to GIMP's image editing features, I would
like to start with a section on opening and developing digital negatives,
so-called RAW files. If you are exclusively taking photographs in JPEG
format, just skip this section and the next, and go on to section 2.3. If your
camera is capable of taking photos in a RAW format, or if you are just curious,
read on.
2.1 JPEG versus RAW
If you are taking pictures not only during good weather, but also at dusk,
at night, or with a flash, then JPEG is not the best format for good pictures.
Photographs shot against the sun are problematic. Keep in mind that the
JPEG format has a color depth of 24-bit (approximately 16.8 million colors).
The results are images in true color. Nevertheless, the lossy compression of
this file format saves file space by blending areas of similar color. This reduces
the amount of information that needs to be stored. Thus, color information
and details are lost. If the light is good, you will also obtain a good result.
Unfavorable light, on the other hand, will make it difficult to obtain good
results, even if you post-process your image. Once the image is compressed
as a JPEG, similar colors are standardized, hence blended together.
The Joint Photographic Experts Group (JPEG) format was developed in the
early '90s. It was soon being used for displaying images on the Web because
of its high compression. It offers small storage size with short download time,
which was important back in the days when the World Wide Web was slow.
With the emergence of digital cameras, it was the best format for the limited
storage space of the early storage media.
To assure optimal image quality, the manufacturers of digital single-
lens reflex (SLR) cameras offer their own storage formats. Even some high-
end bridge and compact cameras offer these so-called RAW formats. If your
camera offers a RAW format, you will find details in the handbook. You will find
the settings in the menu of camera's menus.
Generally, these RAW data formats store the image data on the camera's
chip in the highest resolution without compression with a 48-bit color depth
(about 281.5 trillion color shades). The size of the file is about three times as
large as that of a JPEG with the same amount of pixels. The storage process
takes considerably longer than it does for the JPEG format, which is why the
RAW format is not suited for sports and wildlife photography, where fast
consecutive series of photographs are taken. RAW images are often referred
to as digital negatives. They first must be developed with the help of a suitable
program and saved in another file format before they can be passed on for
further editing. However, the results are usually worth the effort.
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