Fred Weinhaus scripsit:
> P.S. Again,
>
> If you do not need the gamma part of level, then you can do the same
> thing automatically with
>
> convert image1.png -contrast-stretch 0% image2.png
Thanks, tried to use it but couldn't grok docs and my experiments were
inconclusive. One question to documentation:
"Or, if percent is used, black-out at most black-point % pixels and burn
at most 100% minus white-point% pixels."
This applies strictly to number of pixels, not dynamic range of colors?
For example it will clip 4800 pixels on "white and black sides":
convert image1.png -contrast-stretch 1,1% image2.png
not 3 levels from each side (800x600 pixels, 8-bit depth, 255 levels per
channel)?
> It finds the min and max automatically and stretches the image
> linearly so that the min becomes black and the max becomes white.
>
> "The channels are stretched in concert. Specify -channel to normalize
> the RGB channels individually."
So to make auto-level known from GUI graphic programs I need:
convert image1 -channel Red -contrast-stretch 0% \
-channel Green -contrast-stretch 0% \
-channel Blue -contrast-stretch 0% image2
Yes, it looks so. I can almost exactly reproduce GIMP auto-level with
convert image1 -channel Red -contrast-stretch 0.75% \
-channel Green -contrast-stretch 0.75% \
-channel Blue -contrast-stretch 0.75% image2
(range clipping is often done to "strengthen" colors, grrr)
> Above deprecated (but still supported) in IM 6.4.0-11 but now
>
> convert image -format "%[fx:image.minima]" info:
> convert image -format "%[fx:image.maxima]" info:
> convert image -format "%[fx:image.mean]" info:
> convert image -format "%[fx:standard_deviation]" info:
>
> reports values in range 0 to 1. But you can now do math calculations
> within these.
Looks like duc info is true also for other values. For me
[EMAIL PROTECTED] ~/jpegs $ convert 7.jpg -format "%[fx:image.minima]" info:
0.0117647
I would expect 0 because appropriate section of identify -verbose output
is:
Channel statistics:
red:
min: 3 (0.0117647)
max: 215 (0.843137)
mean: 46.261 (0.181416)
standard deviation: 31.5845 (0.123861)
green:
min: 0 (0)
max: 206 (0.807843)
mean: 40.7828 (0.159933)
standard deviation: 32.9262 (0.129122)
blue:
min: 0 (0)
max: 204 (0.8)
mean: 29.8439 (0.117035)
standard deviation: 30.7852 (0.120726)
The same applies to image.maxima
Thank you very much.
m.
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