Irfanview is a great utility for opening and saving in a vast range of
graphics file formats as well as performing a reasonable amount of manipulation
along the way.
It's designed for situations where the Windows Paint program just fails to
cut the mustard.
Effects include blur, emboss, oil paint, edge detection, explosion and
pixellise, while the enhance colours option allows you to adjust red, green and
blue levels along with brightness and contrast. There are sharpening and
resolution adjustments too.
Some of the most obscure formats - such as those native to Sun and SGI
(Silicon Graphics) platforms, along with bitmaps for mobiles - require
additional plug-ins but these, too, are free downloads.
This latest 4.x adds support for a new paint plugin, support for previewing
FLV files, new effects and much more.