Exposure..

[dognose]

I'm working on translating this effect into IM calls.

http://ebin.wordpress.com/2007/03/21/ho ... photoshop/

I'm stuck on reproducing the exposure setting:


I've used the -sigmoidal-contrast 4,0% .. but I'm not sure what else i'd use..

[dognose]

no one has any ideas?

[fmw42]

why don't you do some tests with a gradient image to see what changes occur for different exposure settings. then use my profile script to visualize those changes. profile script is at http://www.fmwconcepts.com/imagemagick/index.html/ then post those results

I started to try that, but I only have PS CS and it does not have the exposure option.

[Massimo C.]

Try with something like this:

Code: Select all

convert in.png -level 20%,80%,0.5 \( +clone -modulate 100,0 \) -compose hard-light -composite -modulate 100,150 out.png

[fmw42]

Try with something like this:

Code: Select all

convert in.png -level 20%,80%,0.5 \( +clone -modulate 100,0 \) -compose hard-light -composite -modulate 100,150 out.png

Was this by experimentation to try to come close or do you have any true understanding of what PS is doing for this exposure panel, in particular any algorithmic information?

[Massimo C.]

Was this by experimentation to try to come close or do you have any true understanding of what PS is doing for this exposure panel, in particular any algorithmic information?

Experimentation. The PS panel gave me a clue: the gamma parameter is afaik the only one i can set in IM.
IM examples always come handy: http://www.imagemagick.org/Usage/color/#level_gamma
Then a sort of contrast mask:

Code: Select all

 ... \( +clone -modulate 100,0 blur xx \) -compose hard-light -composite ...

...without blur
The result needs more saturation (-modulate)

[fmw42]

the real question is the original user trying to duplicate the action of this window in general or just these settings and for one particular image

[fmw42]

I did some experimentation with Exposure in the Mac Preview app and then examined the histograms produced. I think I have worked at what exposure does or at least a good approximation. I have a new script, exposure, that lets one change the exposure amount in an image. See http://www.fmwconcepts.com/imagemagick/index.html

[gomez000123]

nice post,.,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,