Legacy ImageMagick Discussions Archive

The documentation http://www.imagemagick.org/script/comma ... l-contrast is wrong. It says: "Contrast indicates how much to increase the contrast. For example, near 1 is none, 3 is typical and 20 is a lot. Note that exactly zero is mathematically invalid."

It should read, "... For example, near 0 is none, ..."

This is easily shown:

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%IM%convert %SRC% -format "%%[fx:mean] %%[fx:standard_deviation] " info:
%IM%convert %SRC% -sigmoidal-contrast 0.001x50%% -format "%%[fx:mean] %%[fx:standard_deviation] " info:
%IM%convert %SRC% -sigmoidal-contrast 0.100x50%% -format "%%[fx:mean] %%[fx:standard_deviation] " info:
%IM%convert %SRC% -sigmoidal-contrast 0.500x50%% -format "%%[fx:mean] %%[fx:standard_deviation] " info:
%IM%convert %SRC% -sigmoidal-contrast 0.999x50%% -format "%%[fx:mean] %%[fx:standard_deviation] " info:
%IM%convert %SRC% -sigmoidal-contrast 1.000x50%% -format "%%[fx:mean] %%[fx:standard_deviation] " info:
%IM%convert %SRC% -sigmoidal-contrast 1.001x50%% -format "%%[fx:mean] %%[fx:standard_deviation] " info:

Fixed. Thanks for the patch.

snibgo wrote:The documentation http://www.imagemagick.org/script/comma ... l-contrast is wrong. It says: "Contrast indicates how much to increase the contrast. For example, near 1 is none, 3 is typical and 20 is a lot. Note that exactly zero is mathematically invalid."

You are correct about the old documentation. It used to not produce good results below 1 going towards zero. But the zero case has already been fixed for quite a while now thanks to Nicolas Robidoux, so zero is valid and produces a no-change result.

Thanks, Fred. I didn't think of testing zero but you are right, it works fine.

I suggest

Code: Select all

For example, near 0 is none, 3 is typical and 20 is a lot. Note that exactly zero is mathematically invalid.

is changed to

Code: Select all

For example, 0 is none, 3 is typical and 20 is a lot.

I will edit the docs if it is not already changed.

Legacy ImageMagick Discussions Archive

-sigmoidal-contrast documentation

-sigmoidal-contrast documentation

Re: -sigmoidal-contrast documentation

Re: -sigmoidal-contrast documentation

Re: -sigmoidal-contrast documentation

Re: -sigmoidal-contrast documentation