A studio shot on a plain white background that was originally intended to be a cut-out vignette half tone. The large area of plain white and the soft shadow to the right are challenges for the JPEG format because any compression artefacts will start to show up there first.
The restricted palette makes low bit-depth GIF or PNG a possibility and allows the background to be transparent although the file size will be larger than with JPEG.
The image shown is a 6-bit (64 colour) GIF with a transparent (white) background.
|Red Dog - GIF format, 6-bit (64 colours), dithered|
|Red Dog - PNG format, 6-bit (64 colours), dithered|
A full tone photograph with lots of fine detail in the masts and rigging. Although there is a predominance of blue in the shot, allowing a restricted palette to be used, the JPEG gives format better results than the other two and at about half the file size.
The sky and clouds are the most difficult areas for both JPEG and dithered GIFs and PNGs.
|Tunisian Port - JPEG format|
A very stylised photograph that I originally used as a posterised illustration. The large areas of flat colour make the choice between a JPEG and GIF or PNG more difficult.
The JPEG version was slightly smaller than the other two but required a low degree of compression to keep the flat areas from going blotchy.
|Sun Arch - JPEG format|
This image is well suited to low bit-depth GIF or PNG. If saved as a JPEG, even the lowest compression displays artefacts on the sharp edges and requires a file that is three times bigger than it needs to be.
|Big Deal - GIF format, 4-bit (16 colours), not dithered|
|Big Deal - PNG format, 4-bit (16 colours), not dithered|
This is the type of image that works best in GIF format. With only one foreground colour and one background colour plus the anti-aliased fringe, it only needs 3 bits (8 colours) and gives a very small file size.
Note that these graphs are at a larger scale than all the others.
|Simple Headline - GIF format, 3-bit (8 colours), not dithered|
|Simple Headline - PNG format, 4-bit (16 colours), not dithered|