RGB to LAB

Questions and postings pertaining to the usage of ImageMagick regardless of the interface. This includes the command-line utilities, as well as the C and C++ APIs. Usage questions are like "How do I use ImageMagick to create drop shadows?".
Post Reply
redsmith

RGB to LAB

Post by redsmith »

Hello. Quick question:

when converting an image to the LAB colour space using GIMP; then doing the same with IM there is quite a difference between the output of the applications in the L channel. Am I misunderstanding something or is it a bug of some kind?

(ImageMagick, left; GIMP, right )
Image Image

Thanks in advance, R.
redsmith

Re: RGB to LAB

Post by redsmith »

Bump. Any reply would do - even if it's to point out I'm a numbskull; and to read the docs more closely.
User avatar
fmw42
Posts: 25562
Joined: 2007-07-02T17:14:51-07:00
Authentication code: 1152
Location: Sunnyvale, California, USA

Re: RGB to LAB

Post by fmw42 »

one of the two is using the log (option) of LAB for the L component. do a google search on LAB and see what it is supposed to be and if there are controls for log or not.
redsmith

Re: RGB to LAB

Post by redsmith »

Hello, fmw42, and thanks for the response. I haven't got the time to chase technical papers around but taking your mention of 'log ' as a starting point I applied an '-evaluate pow 3' to the separated channel and got something more like the expected result (from GIMP). I think I was mistaken in thinking the GIMP decompose to layers would give something like a pure channel separation. I'll experiment a bit further. Thanks again.
Post Reply