CHROMiX

Clipping in image plots and human gamut

Hello

I have a Lab tiff comprising the following 21step colour sequences:

  • [50 -128 0] -> [50 127 0]
  • [50 0 -128] -> [50 0 127]
  • [50 -128 -128] -> [50 127 127]
  • [50 -128 127] -> [50 127 -128]

When I plot it, the ‘b’ coordinate gets clipped to approximately 90 and all points relative to colours exceeding this limit shift towards the ‘a’ axis.

If the L value changes from 50 to 100, the clipping moves into the blue region limiting ‘b’ values to the [-75 127] range.

Finally, L=10 restricts '‘a’ to [-42 127] and ‘b’ to [-128 25].

Is this due to the software taking into account human gamut boundaries?

Thank you a lot.

Giordano

My configuration:
Colorthink Pro 3.0.1b5 for macintosh
Mac OSX.4.6
G5 Quad with GeForce 7800GT
Plenty of ram

At 4:35 AM -0700 7/1/06, Giordano Galli wrote:

it shouldn’t be, no.

Is it a 16 bit Lab file? I’m not certain ColorThink reads them properly yet - one of the problems with 16-bit Lab files is they can appear in a number of different forms because the TIFF spec was not updated for 16-bit Lab and so it floats…

please submit the file using the new feedback system in ColorThink Pro 1.0 beta and we’ll take a look.

Regards,

Steve


o Steve Upton CHROMiX www.chromix.com
o (hueman) 866.CHROMiX


Post generated from email list

Hi Steve

The Lab file is 8-bit encoded.
I’ve submitted a feedback item as per your instructions.

Thank you a lot. I greatly appreciate your help with this.

Giordano

Steve Upton wrote:

please submit the file using the new feedback system in ColorThink Pro 1.0 beta
and we’ll take a look.

Sorry to bother you further, but this question of mine relates to an issue I’ve been investigating for a while now and is rather important to me: I’d simply like to know whether you were able to reproduce the ‘clipping’ in-house. As I wrote you, it merely suffices to open my image in the grapher.

Thank you for your interest.

Giordano