[softwarelist] Re: Loading pictures into OPro
- From: Chris Johnson <chris@xxxxxxxxxxxxxxxxxxxxx>
- To: davidpilling@xxxxxxxxxxxxx
- Date: Mon, 23 Jun 2008 15:54:45 +0100
In article <23a1eab34f.tim@xxxxxxxxxxxxxxxxxxxxx>,
Tim Powys-Lybbe <tim@xxxxxxxxx> wrote:
> GIF also is lossy
Not strictly true that GIF is lossy - like sprites, BMPs etc, all the
original information is retained. However, GIF is only 256 colours,
so in that sense some colour information may be lost if a 24-bit
colour image is converted to the 8 bit GIF format. For 1 - 8 bit
images, no information is lost.
JPEGS (and e.g. MP3s) are lossy because various techniques are used
to discard what is 'considered' to be non-essential information to
allow the high compression ratios. The information discarded can
never be recovered.
JPEGS are not recommended for colour images (or B&W) that have areas
of constant, or near constant, colour, since the algorithm used to
produce a jpeg will introduce artifacts, often seen as patches of
slightly differing colour across a constant colour. Hence jpegs are
ideal for real photos, since any artifacts are hidden by the
constantly changing colours across the image, whereas for a e.g. Draw
image, with large areas of constant colour, jpgs would not be a first
choice. Sprite, TIFF, GIF would be better. PNG also, which is a
lossless compression method, and also 24-bit with masks.
If you go through a long sequence of only load/save/load/save with a
jpeg, the quality slowly deteriorates, whereas with GIF, the final
image will be identical to the original GIF.
Sorry for rambling on - I've obviously got nothing better to do!
Chris...
--
Chris Johnson
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