What Photoshop fill for 18% grey card?

Started Dec 16, 2005 | Discussions thread
Petruska Veteran Member • Posts: 8,939
Nice data at that link....

pixelgenius wrote:

Petruska wrote:

is that I would like to meet the person that can print with an inkjet printer a “true” 18% gray compared to a commercial gray card (ColorChecker). Just produce a color in PS using any one of the suggested numbers, print it with many different printers and you will have many different looking shades of gray prints. Matte papers versus luster, satin, gloss are also going to look different.

Later today I will spot read my Xrite ColorCheckers 18% patch using my I1Pro’s just to see what Lab and RGB values are indicated.

Bob P.

There is this too:


ColorChecker_RGB_and_spectra.xls (155 KB .zip) (April 2012)This Excel spreadsheet contains:oRGB tables for 19 spaces, and L*a*b* (D50) values derived from averaged spectrums;oRGB tables for 19 spaces, and xyY (D50) values derived from GretagMacbeth L*a*b* D50 data (2005);oRGB tables for 19 spaces, and L*a*b* (D50) values derived from CIE (1931) xyY data (1976);oAveraged spectral data with Standard Deviation tables (from 30 charts)

I measured the #23 patch (supposed to be the 18% gray) on the my ColorChecker Passport with my 3, I1Pro Rev D UVcut spectrometers using I1Profiler.

L*a*b measurements, D50 illuminate....

#1 I1Pro   36.41   -0.58   -0.35

#2 I1Pro   36.34   -0.62   -0.46

#3 I1Pro   36.37   -0.61   -0.33

Not exactly the same numbers as in the spreadsheet data but close enough.  My measurements do indicate to me that my 3 I1Pro spectrometers track closely to each other.  The #2 spectro has 15 hours of lamp time, the #3 has less than 60 seconds.  Thus anyone looking to buy a used I1Pro shouldn't shy away from one with a lot of lamp hours on it.

Bob P.

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