Legacy ImageMagick Discussions Archive

Should this command line burn pixels?
If so, what are the formulas it uses, and are these formulas listed in the documentation?

If not, there appears to be a bug in normalize....

img.jpg:


img-normalized.jpg:


Version: ImageMagick 6.3.6 10/01/07 Q16 http://www.imagemagick.org
Copyright: Copyright (C) 1999-2007 ImageMagick Studio LLC

Cheers
rling

-normalize is a simple command that fails in your case.

It findes the highest and lowest values in the image, takes off 1% more, then scales all the channels so those values are the maximum/minimum for each channel.
It is rather brain dead.

The problem for you is that 1% Instead you will need to use -contrast-stretch 0%, which works in exactly the same way but lets you specify the about of extra inward color to take off.

That will remove the extra 'burn' you see.

When I have finished work on image distortions I will be looking at the color methods developed by Fred Weinhaus in his IM scripts for auto-levels and other image enhancement. See http://www.fmwconcepts.com/fmw/fmw.html

In the mean time you may like to use his scripts for your images.

Thanks anthony.
I thought this was a bug in normalize but later worked out that it seemed to be equivalent to -contrast-stretch 1%, and often it looks good. I began to use -contrast-stretch 0 instead. It looks like a lot more than 1% of pixels get burned by normalize but I guess when the dynamic range is small that is what has to happen.

Can the percentage use a decimal point? Seems to not work on Windows, I'm wondering if the command shell is doing something to it since % has special meaning on Windows.

It probably can. most arguments are floats. though if your IM is only a Q8 you may have quantization issues. If a percentage is not specified the value is the quality dependant value.