Legacy ImageMagick Discussions Archive

Hello,

i am completely new to Imagekick and i need to convert different types of images to the LAB colorspace.
I Am currently using this command: The problem is, that this command seems not to work for ECI-RGB images and CMYK images.
If I convert a CMYK image to LAB, the image looks completely oversaturated in magenta and cyan.
If I convert an ECI-RGB image to LAB, it is a bit darker than the original.

Help would be greatly appreciated,
Thanks

Please, always provide your IM version and platform when asking questions, since syntax may differ. Also provide your exact command line and if possible your images.

See the top-most post in this forum "IMPORTANT: Please Read This FIRST Before Posting" at http://www.imagemagick.org/discourse-se ... f=1&t=9620

For novices, see

http://www.imagemagick.org/discourse-se ... f=1&t=9620
http://www.imagemagick.org/script/comma ... essing.php
http://www.imagemagick.org/Usage/reference.html
http://www.imagemagick.org/Usage/
https://github.com/ImageMagick/usage-markdown

Note that for ImageMagick 7, convert is replaced by magick; otherwise, you are likely using ImageMagick 6.

Try converting from eci-rgb to srgb with profiles. Then convert to lab with -colorspace lab. I suspect ImageMagick does not know the eci-rgb colorspace, so you cannot convert from it using -colorspace. But you could with an eci-rgb profile. See http://www.eci.org/en/downloads for profiles.

Or use profiles to go from eci-rgb directly to lab.

Can you post a link to one of your eci-rgb files?

The Version i Use is ImageMagick 7.0.7-38 Q16 x86_64 2018-06-02.
The System i am on is macOS 10.13.5.

Using this Command i get the following result (on the left is the in.tif, on the right the out.tif):
https://drive.google.com/file/d/1hJAjGN ... sp=sharing

What software do you have that is reading and displaying Lab images? What data format does it expect? IM writes unsigned integers. Perhaps your reader software expects signed integers.

I suggest you try with ordinary photos, not images that have only three colours: black, white and some other colour.

WEll, i made progress. I split the conversion into two steps:
At first, i converted the original image to a sRGB colorprofile using Then, i converted the resultfile to LAB: But i needed to install Imagemagick with to get that working.

The result: The image i get from the first command (out.tif) looks completely identical to the original.
When i perform the final command (to LAB), i can notice a slight shift in color. barely noticable. But it is there. Any idea how i can get rid of that?
I Noticed that the color profile that the image has that i want to convert to LAB, makes a big difference. If the image is in ECI-RGB, it is darker after i converted it. If it is in sRGB, i notice only a slight color shift. If it is in a CMYK-Profile, it looks completely different.
That leads me to the question: is there a Colorprofile that is better suited for the LAB conversion than sRGB2014?
Or is there any magical parameter that i can add to the second command to get rid of the color shift?

If you do not start with sRGB image, then you will likely need a correct profile for the input, if there is not one attached to the input. So you may need to find an ECI_RGB profile from the page I reference and use two profiles, eci_rgb and then sRGB before you go to LAB. You may also be able to find an LAB profile and then just use the eci-rgb to lab profiles.

Can you post a link to an example ECI_RGB image?