P3D Re: Scanned Stereo pair manipulation software...

[John Ohrt <johrt@xxxxxxxx>]

Dylan The Hippy Wabbit wrote:

> There is no such animal as an uncompressed JPG.

Actually, such a file can occur, but you can't generate one on command
:-)

In the lossless compression mode, the output file will only be
compressed if the resulting file would be smaller than an uncompressed
file.  This is not true of .gif and some other file formats.

>  I know the compression
> setting control often reads 0-99, but it's just an arbitrary number.
> You're not meant to take it literally.  You might mean "Set the
> compression to it's minimum."  If you do you are probably throwing the
> baby out with the bath water.  A moderate compression setting will save
> quite a bit of space (and web server bandwidth) without having any visible
> effect.

  The 0-99 control is more of a quality setting, IMO.  As you noted the
effect is non-linear.  The lower the quality, the greater the losses
permitted, and usually the greater the compression achievable.  Do NOT
get sucked in by claims that selecting 100 is stupid.  It depends on the
implementation.  In some cases, the setting means use lossless
compression.  Read the docs.  

Finally, the better JPEG compressors aslo provide optimization by
fiddling with the default parameters.  If you have it, use it.  Any
reader can decode the image.

Regards,
John



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