the physical size in inches or centimetres with an image editor
will also help with the reduction in the other important dimension
– file size. (Unless you just drag the handles to resize an
image in Word or a web editor like Dreamweaver which has no effect
on file size at all – that’s why you should use an image
editor first and then put it into Word or Dreamweaver.)
Halving the width and depth
will usually result in a file size of 25% of the original.
In these illustrations, examples of how the flower1 picture used
earlier in this section appears at a range of quality or compression
settings are shown after a reduction in height and depth dimensions
achieved a reduction to about 270Kb file size – still much
too big for most uses.
Literally millions of colours
and shades are used in photographs. An image file stores the combination
and position of colours used for each pixel. So lowering the number
of colours that can be stored reduces file size. The processes used
in the various methods of compressing a picture take care of this
A range of compression from
high to low is shown here for a picture of a flower. The Joint Photographic
Experts Group developed the commonly used JPEG file format, usually
shown as .jpg as the filename suffix. It works well for photographs
where thousands of small areas of different colours are invoved.