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JPG, GIF and BMP Image Formats
One of the services that I offer is teaching people HTML
coding. There are a lot of things to remember and the thing
that seems to be forgotten the most, is making sure that images
have the right extension on them. I mean, you have a GIF (image.gif)
file, but you in the HTML, you want try to bring up the same
file, but with a JPG extension (image.jpg). This of course
will cause the browser to give you a nice little red x.
All this would be solved if there weren't so many different
graphic formats. Of course, each format has a different format,
so the solution is to pay closer attention, and also to learn
what each format is, and why they are used in different situations.
I will briefly describe 4 basic graphic formats.
The first thing that we need to understand is that there
are 2 types of image compression, lossy, and lossless. Different
image formats use different compression formats.
Lossless compression compresses an image without
removing any data. Lossy compression will discard
some of the data so that it can be compressed more. Lossy
images typically wouldn't have as many colours available.
JPG, JPEG, or Joint Photographic Experts Group Format
images have lossy compression. This is a common format
used when saving photographs. Doesn't save line art very
well.
GIF, or Graphics Interchange Format uses lossless
compression. The image quality might not be that high,
but there are sharp edges. This is one of the reasons
why it is used on web pages for small graphics. It can
retain the sharp edges. Another reason is that GIF images
can be used on PCs and Macs.
TIF, TIFF, or Tagged Image File Format is also
cross-platform between Macs and PCs. There isn't really
any compression with this format and the file size can
be quite large.
BMP, or Bitmap Format uses a pixel map which contains
line by line information. It is a very common format,
as it got its start in Windows. This format can cause
an image to be super large.
Below is a colour sample of 2 of the formats. The GIF image
quality is very poor. The JPG is a nice files size and looks
good.
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GIF, 4583 bytes |
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JPG, 7099 bytes |
Below is a black and white sample of the 2 formats. The quality
of the images is all quite good, but in this case, the GIF
file is the best choice.
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GIF, 2782 bytes |
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JPG, 6392 bytes |
Just remember when you are working with images to pick the
best format most appropriate for what you are doing and for
the type of picture it is.
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