G4URH Picture Formats
There are three major graphics formats on the web: GIF,
JPEG, and PNG. Of
these, PNG has the spottiest support, so that generally leaves one to chose
between GIF or JPEG format. There are many other available formats in which to
save image files; it is likely that many of your web site visitors will not be
able to view your files.
JPEG is a lossy compression technology, so some information is lost when
converting a picture to JPEG. Use this format for most photographs because the
images will be smaller and look better than a GIF format picture.
________JPEG Image_______________GIF Image_______
Notice the easy-to-see graininess of the second photo and the
GIF photo would still have a larger file size without the quality of the JPEG image.
It is not good to edit and re-edit a JPEG image because more detail is lost
with each subsequent save. If you want to edit the picture multiple times, save
it in a different format (like TIFF) on your machine, but post it to the web as
GIF files are better for figures with sharp contrast (such as line drawings,
Gantt charts, logos, and buttons). One can also create transparent areas and
animations with GIF images. A GIF image has a maximum of 256 colors however, so
images with gradations of color will not look very good.
To make the picture quality difference
more noticable, I saved the JPEG image at 30 quality. Notice the blurry
portions around areas of high contrast (such as text).
GIF is a patented file format technology. PNG is an open-source standard
that can be used for many of the applications of GIF images. PNG is better than
GIF in most respects, providing more possible colors, alpha-channel
transparency, and color matching features. The PNG format is not as widely
supported as GIF, although it is supported (to differing degrees) on the
version 4 and later browsers.
If you are interested in PNG images, visit the
official PNG home site or the
W3C PNG web page where you can
find some browser tests.
Other picture formats
BMP or bitmap files are pictures from the Windows operating system. Using
these on a web page can cause problems because they cannot be viewed by most
browser. Stay away from using BMP files on the web.
TIFF images have great picture quality but also a very large file size. Most
browsers cannot display TIFF images. Use TIFF on your machine to save images
for printing or editing; do not use TIFFs on the web.
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