On Thu, 27 Apr 2000 19:07:39 +0200, Gilles Tran <tra### [at] inapginrafr>
wrote:

>See my post in p.unofficial.patches.
>Below is an example of a highlight/midtone/shadow post-processing (done
>with Micrografx Picture Publisher <SNIP>

What you seem to have done is to simply raise the contrast of the
image. In most image manipulation programs this would actually require
both an increase in contrast, and a general darkening of the image.

If this doesn't make sense to anyone, why you need to perform two
simple tasks to achieve one simple effect, I can explain. Most image
manipulation programs don't rotate the slope of the response curve
about it's midpoint, but rotate it around the 0 point. Looking at the
charts I attached to this post might explain what I mean by that.

I have attached my recreation of your effect. I have also included
pictures of curves that represent what I did to the tonal range of the
image, labeled "before" and "after." In keeping with my earlier
listing of formulas for such effects, here are the formulas used:

    Rout = (Rin*1.6)-0.3
    Gout = (Gin*1.6)-0.3
    Bout = (Bin*1.6)-0.3

My version looks pretty darn close to yours, and we would need to work
with a lossless image format to really get any closer. If you want to
post a PNG, I'll send back a PNG to match yours. Then we won't have to
worry about how much precision we might be losing through JPEG
compression. 

If this sort of effect is what you want, it can be achieved with
"iso-functions" applied to tonal response.

Later,
Glen Berry

( Remove the "7" from 7no### [at] ezwvcom to email me. )

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