Extracting black chroma from L*a*b* data

[shewhorn]

This was inspired by this thread:

http://www.luminous-landscape.com/forum/index.php?topic=44889.0

I have a bunch of linearization targets that I've scanned in already. I'd like to graph the chroma curves using a spreadsheet. Extracting chroma doesn't seem to be too difficult using this equation:

sqrt( a^2 + b^2 )

So a little back story if you don't want to read the entire thread... Scott Martin suggested using ColorBurst to plot chroma curves to determine optimal ink levels when building a new media type. I was just curious to see if I could replicate the graphs I've already done using ColorBurst by importing the scanned data I already have into a spreadsheet and graphing it there. I was successful for cyan, magenta, and yellow. The black threw me for a total curve though. For L*a*b* values of 22.9, 2.16, 2.12; ColorBurst is showing a Chroma of 77.1. The value I'm getting is 3.02655. Now, that kind of makes sense to me seeing as how chrominance is supposed to convey color information and black, black is black. So what is ColorBurst doing to get their higher value?

Cheers, Joe

[Mussi_Spectraflow]

Hey Joe,
I think you're doing everything right, that's the correct formula for determining chroma. A value of 77 would represent a very saturated color so something isn't right, are you sure that not displaying hue or something else. Is not then it might be a bug in how things are displayed.