Colorchecker Charts, RGB Values, & Help Me Tim !!

[Mark_48]

I've been using as a monitor image reference the "Printer Test file" from www.digitaldog.net . I've done a monitor calibration with the Pantone Huey and the Printer Test file seems to be an accurate rendition on screen to my eye and the embedded GretagMacbeth Colorchecker chart included in the image compares well with charts included in the book "Real World Color Management". In the book the RGB values of each square is indicated for the Colorchecker chart. Taking the eyedropper sampling tool in PS7 and looking at the RGB values in the squares from DigitalDogs site the values do not match. I then took and modified the chart filling each square with the values from the book. This modified chart does not compare well with the original chart or the one in the book. The RGB sample numerical values do not change using different monitor profiles, although the visual color renditions do slightly, which I would expect.
Can PS7 create incorrect colors using RGB values and/or could the eyedropper sampler misread the RGB values - PS7 not calibrated ? Or am I not comprehending something in how I'm making a comparison.
Below are two charts, both cropped from the Printer Test file. The first has no intentional modification to it's color rendition. The second image has the squares filled with RGB values from the book "Real World Color Management".

[tim]

I have no idea, nor why you care. I think you need the services of our King Measurebator (http://photography-on-the.net/forum/member.php?u=28729), Curtis N.

So long as your prints look pretty much like your monitor stop worrying.

[René Damkot]

The values of R,G, and B for a given color will vary depending on the document color space.
Apart from that, I agree with Tim ;)

[RedWingNut]

If you play around with a Huey or similar, and adjust the gamma or brightness or contrast, the RGB values of the colors don't ever change but the appearance of those colors does.

Is this your problem?

[maderito]

As René said, RGB color numbers depend on the color space.

Digital Dog's Macbeth chart was saved in ColorMatch color space. I believe Fraser's chart quotes Adobe RGB values. (My copy of Fraser's Real World Color Management has LAB values - but I've seen his RGB values somewhere).

Even if you got your color spaces right, I wouldn't expect 2 versions or quoted RGB values of the Macbeth chart to be identical - unless they are "synthetic charts" - that is created in PS by specifying RGB numbers, not by actually photographing the original chart.

Digital Dog's file is a printer test file. You print it and assess if the colors are right or not. Also, it should look good (skin tones, etc) on your calibrated monitor.

[Mark_48]

Thanks all. It indeed was the color space that was causing the variation in numbers and color tone. At least I feel more confident the Huey is doing what it should.