Subject: Which graphic format to use
From: ACRE NL
Date: 11/7/2001, 11:04 AM


     Paul wrote:

     Chuck please zoom in on one quarter of the drawing at a time and
     save each zoom as separate jpg. Send all four jpg's I think that
     should do the trick.

     Mark Wrathall wrote
     Line drawings should be saved as .gifs and photos as .jpg.

     A basic overview of why.

     A bmp saves three bytes (0-255 red, 0-255 blue, 0-255 green) per pixels for
     all pixels. This is simple but very memory inefficient. A featureless black
     background takes as much memory as fine detail.

     Jpgs compress by comparing pixels and just recording the changes. The more
     uniform area, the more it can be compressed. Think of blue sky. You can have
     one 3 byte pixel to define the color, then the next ten are defined as "
     same as your mate :). The more fine detail, the less information you can
     throw away, therefore the bigger the file. Using the JPG quality setting
     defines the tolerance of what the program is to consider as "same as your
     mate. With low quality selected you get stepped banding instead of gradual
     color gradients. Because jpgs define relative to control points, they can
     generate blocky artifacts, making it unsuitable for line art.

     Gif files use a limited palette of up to 256 colors (although it can be any
     256, the palette for that picture is part of the file). It compresses by
     throwing away nuances of color. A line diagram has no nuances, and normally
     only a few colors. Therefore .gifs are loss less for drawings, but make for
     crappie photos with the limited palette. Note that gray scale images are only
     256 shades, so this is also loss less in .gif format.

     Tifs are loss less, but have limited compression routines. Mainly interesting
     for photography as it supports 16 bit color.

     Very interesting. I've just jpeg'd everything here to fore. Thank you, Mark ........Jerry

It is no problem for me as I can quickly convert among formats.

Paul Lamar
 
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