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CHAPTERCreating Images 3
Choosing the Right Format
Because the JPEG and GIF formats were specifically designed for
a particular image type, each is inherently more efficient when
used on the correct type of image. Therefore, an image that
should be saved as a JPEG will be larger if you attempt to save
it as a GIF, and vice versa. GIF PNG
Scale and Crop Images
Images with needlessly large pixel dimensions will also be
needlessly large files. Using a good image-editing tool to reduce
the dimensions of the image dramatically reduces its file size.
You can also crop unneeded portions out of the image to reduce
its size.
Resolution
Image resolution describes the number of pixels per inch in an image.
Whereas images for print need to have a high resolution, images for the
Web should never be more the 72 dots or pixels per inch. Many computer
screens are simply incapable of displaying higher-resolution images, so
keeping the image at a higher resolution simply wastes file size.
GIF and PNG Features
GIF supports optional features such as animation and
transparency. PNG supports transparency. Adding these can
make your image look better, but also adds to the file size.
Therefore, choosing to not use these features reduces the
size of the images.