LAB: why no "c" channel?

Snapper

Greetings all!

I've been lurking for several months and have picked up a massive amount of information from the learned folk who frequent this forum: I thank you all most sincerely.

I read a post some weeks back where someone explained why it was not necessary to have a Red/Cyan channel in LAB, but I can't find it again and I'm having trouble coming up with useful words to search on.

Could someone please run this one past me once more.

Thanks!

DavidTO

Snapper wrote:

Greetings all!

I've been lurking for several months and have picked up a massive amount of information from the learned folk who frequent this forum: I thank you all most sincerely.

I read a post some weeks back where someone explained why it was not necessary to have a Red/Cyan channel in LAB, but I can't find it again and I'm having trouble coming up with useful words to search on.

Could someone please run this one past me once more.

Thanks!

My understanding is that it's because you can describe red and cyan with magenta, blue, yellow and green.

Red is magenta and yellow, for instance. Cyan...I'm not sure, I'd have to go review the materials. I guess I get downgraded for that.

Have you gone through our LAB reading group?

Snapper

DavidTO wrote:

My understanding is that it's because you can describe red and cyan with magenta, blue, yellow and green.

Red is magenta and yellow, for instance. Cyan...I'm not sure, I'd have to go review the materials. I guess I get downgraded for that.

Have you gone through our LAB reading group?

Thanks for your quick reply! Yes, I'm gulping down all the LAB tuts I can find - it's a fascinating colour space, and the more I go there the more I like it! I'll keep trawling through the posts to try and find the answer.

DavidTO

Snapper wrote:

Thanks for your quick reply! Yes, I'm gulping down all the LAB tuts I can find - it's a fascinating colour space, and the more I go there the more I like it! I'll keep trawling through the posts to try and find the answer.

Get the book.

LiquidAir

Magenta + Yellow = Red
Green + Blue = Cyan

When the a and b channel have the same value (a = b) you are somewhere on the Cyan - Red axis.

Nikolai

DavidTO wrote:

Get the book.

I second that

The reason why LAB (aka L*a*b, from CIELAB) has chosen this particular color combination is rather academic and mostly historical. Dan goes into some details about that, but the real matter is: yes, it's possible to use many different combinations, but here's one, it works, so it kinda boils down to Occam principle. We have way too many DVD, HD and media card formats to start colorspace format war once again (as if we don't have enough colorspaces already:-).