Convert gray content of gray/white image to black ?

[Rye]

Well, let's say I have this picture:



Let's assume I want to change all the gray color in this picture to plain black.

Is there a command to have imagemagick change all grey of this image (preferableby using grey [Hex: C8C8C8] to black [Hex: 000000] ?





I ask for a way to use the color value itself so I could use this code on more complicated examples in future.
[spoiler]


For example changing a certain yellow tone in this image to a special orange or something[/spoiler]

[snibgo]

For that image:

Code: Select all

convert Clipboard01.png -auto-level p.png

Sometimes contrast-stretch works better, or level, or level-colors.

See http://www.imagemagick.org/script/comma ... ptions.php

[Rye]

Is this also possible by using the HexCodes I mentioned

[snibgo]

Code: Select all

convert Clipboard01.png -level-colors #c8c8c8,white p.png

[fmw42]

Code: Select all

convert Clipboard01.png -fuzz 10% -fill black -opaque "#c8c8c8" result.png

change the fuzz value to whatever works best

[anthony]

That latter (using -opaque) is probably not good as the image is full of shades of gray, and -opqaue is a boolean (all or nothing) type operator.

-level-colors will give ber find control over the transformation. -level will give grayscale control -normalize and -auto-level will automatically maximise contrast (though with different 'level' selection)

[Rye]

Ok, this works really well. Thanks.

Another question:

If I wanted to change from one hex code to a specific other one.
What woudl I have to change in that code of yours ?

[fmw42]

Code: Select all

convert image -fuzz XX% -fill "newhexcode" -opaque "oldhexcode" result

[Rye]

Thanks ! Just what I was looking for!

[fmw42]

see
http://www.imagemagick.org/Usage/color_basics/#replace