Digital BW, The Print

Howard,
I think your barking up the wrong tree... Your X-rite methodology is designed for a color response. I believe your building profiles and expect them to function as a linearization. They are merely a color correction look up table.. So the expectation of a linearized gray ramp can't happen that way.. X-rite does include linearization capabilities in some of their higher end software but in truth it doesn't work that well today or at all with printers that have more then 4 channels.. They added that feature to deal with spot colors I believe. 

jimbo----- Original Message ----- 
  From: howardhamilton3333 
  To: DigitalBlackandWhiteThePrint@yahoogroups.com 
  Sent: Tuesday, October 19, 2010 9:40 AM
  Subject: [Digital BW] camera profile


    


  I recently purchased the X-Rite Colorchecker Passport and have been doing a bit of work looking at the results, especially the gray scale produced for the camera profile (used in Adobe Camera Raw and/or Lightroom). I shot the Gretag Macbeth pattern under a variety of lighting conditions for which I also set the white balance on-camera by shooting a gray card and the white card that came with the Passport. The camera is Nikon D300. Since the Lab and RGB values for the color patches are readily available on-line, I was able to compare the values photographed with those of the color chart. I should note that I also bracketed the shots so as to get the white value of the pattern (241, 241, 241 in RGB) as close as possible to the card's value (241, 241, 241 in RGB). I find that I am consistently getting a non-linear gray response from the camera profile. I can readily adjust the near-white and near-black with exposure and black adjustments, but all intermediate gray values are higher than the values reported for the pattern. I can correct these values in ACR using the "Point" adjustments curve, and the results look good. I am, however, surprised that the X-Rite camera profile does not seem to get the gray values right. Has anyone here looked at this?

  I assume that the X-Rite program attempts to generate the best over-all color match using some kind of algorithm, but it isn't intuitive that it would need to screw up the gray values. I don't know, but it seems likely that X-Rites program is based on the earlier work by Bruce Frazer, the ACR Calibrator, etc., but I believe the gray values were set in those studies before attempting to set color values. 

  I should note that I see the same discrepancy in the gray values on the X-Rite sample download.

  Howard 



  

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