GIMP tools - BDA

GIF (Graphics Interchange Format)
GIMP 18
It is a graphics interchange format, introduced by CompuServe in 1987. At that time it
was used for transferring images by computer networks. In 1989 the format was
enhanced, which added support for transparent background and animation. This format
has the extension .gif. It is a compressed format and very suitable for compressing
images of one colour, i.e. one colour by vertical or horizontal pixels. It uses LZW 11
compression which compress without losing images with up to 256 colours. This format
is usually used for drawings and charts. It supports transparency, animation. In this
format files take the least space, therefore they are suitable for creating banners,
buttons, logotypes and any other website elements.
This graphics format is very popular on the Internet. It is supported by all browsers and
most of the graphics editors. Due to the qualities of a compression algorithm (limitation
of the colour palette up to 256 colours or less, compression with expander according to
horizontal lines), it may deliver very small graphics files, where the initial image has large
areas of uniform colour. However, it is not suitable or barely suitable for saving photos
and images with large horizontal gradients. The file saved will be large and of rather
average quality.
GIF has another wonderful quality, namely line by line data storage. Lines are grouped
and their order in the file is changed. This leads to the possibility to upload the image in
several stages. When we have only part of the file, we can see it all only with a lower
resolution. This possibility is widely used in websites. Here, the user has to remember
that such saving increases the size of a file.
Advantages of the format include good compression, animation support and line by line
data saving. Transparency is only partially supported.
The drawback of the format is low colour depth (8 bits) and a limited number of colours
(256).
JPG (Joint Photographic Experts Group)
It is a wide spread graphics format, supported by all browsers and many graphics
editors. The common filename extensions for this format are .jpeg, .jfif, .jpg, .jpe,
however .jpg is the most common one. The image saved in the JPEG format does not
lose its quality. During the compression process, an image is divided into blocks. Each
block has it own colour palette, on the basis of which it is encoded. As a rule, not all
colours used in the image participate in the compression of a block, therefore the
palette is rather limited (it also depends on the selected quality parameter). If an image
has many sharp colour transitions, a high level of compression leads to a distinctly
artifacted image (a form of noise around contrasting edges). This may be avoided by
choosing a higher quality parameter. In such a case, the file size considerably increases,
which means low usage of the format. This format does not support the transparency
effect.
11 Lempel-Ziv-Welch.