MACBETH Color chart corrections with PS

I would like to fine tune a Macbeth color chart I got on the internet with Photoshop 5.0 LE. I got the RGB values for each patch no. Can anyone advise me on how to modify each patch that I have to the correct patch. For example, my patch no 18 reads RGB 0, 134, 169 and the correct is 0, 148, 189. How do change mine to the correct RB values?
Do I go to hue saturation and do trial and error?
Is there any place I can type in the correct values and have the patch turn out correct.
Can I make my own chart by typing in the correct values and have Photoshop make the colors?
Thanks for any advice on this, Rick

"Stromer2" wrote in message

I would like to fine tune a Macbeth color chart I got on the internet

with

Photoshop 5.0 LE. I got the RGB values for each patch no. Can anyone

advise

me on how to modify each patch that I have to the correct patch.

Depending on your source of the chart, you shouldn't need to change the values.

For example, my patch no 18 reads RGB 0, 134, 169 and the correct is 0,

148,

189. How do change mine to the correct RB values?

You've probably got a Color Management issue. I'm not sure about PS 5.0 LE, but that may not be fully Color Management enabled. So you need to ask yourself the question; for what purpose you need to get certain RGB values? If you are working in an sRGB workflow (or another one), you could try some of the versions available at:
http://www.brucelindbloom.com/ColorCheckerRGB.html .

Do I go to hue saturation and do trial and error?
Is there any place I can type in the correct values and have the patch

turn out

correct.
Can I make my own chart by typing in the correct values and have

Photoshop make

the colors?

See the above link, but the easiest way is getting one of the download files on that page (in Lab colorspace), and convert the profile (not sure if PS5LE allows that). Second best option is creating your own chart with whatever values you want.

Bart

From: (Stromer2)

I would like to fine tune a Macbeth color chart I got on the internet with Photoshop 5.0 LE. I got the RGB values for each patch no. Can anyone advise me on how to modify each patch that I have to the correct patch. For example, my patch no 18 reads RGB 0, 134, 169 and the correct is 0, 148, 189. How do change mine to the correct RB values?

Double-click on the foreground color icon and in the dialog box enter the RGB values. Then use a selection tool (either rectangular marquee or magic wand should work) to select the box with the color you want to change, then do Edit

Fill with foreground color.

Bill

On 19 Dec 2003 14:43:44 GMT, (Bill Hilton)
wrote:

From: (Stromer2)

I would like to fine tune a Macbeth color chart I got on the internet with Photoshop 5.0 LE. I got the RGB values for each patch no. Can anyone advise me on how to modify each patch that I have to the correct patch. For example, my patch no 18 reads RGB 0, 134, 169 and the correct is 0, 148, 189. How do change mine to the correct RB values?

Double-click on the foreground color icon and in the dialog box enter the RGB values. Then use a selection tool (either rectangular marquee or magic wand should work) to select the box with the color you want to change, then do Edit

Fill with foreground color.

Bill

It would be a good thing to be able to accurately reproduce the chart, especially since new ones are $80. Does anyone have a workflow idea for how to develop an ink/paper ICC profile by use of a color reflection densitometer (such as the Macbeth or X-Rite)? Also, could the Kodak cal charts work as well in this application?

RogM writes:

On 19 Dec 2003 14:43:44 GMT, (Bill Hilton)
wrote:

<snip>

It would be a good thing to be able to accurately reproduce the chart, especially since new ones are $80.

Well, you can't. Each patch is not only of a specific color, but has a specific spectral reflectance. If you managed to print one that is a perfect match to the real ColorChecker, it wouldn't be under different lighting conditions.

Does anyone have a workflow idea
for how to develop an ink/paper ICC profile by use of a color reflection densitometer (such as the Macbeth or X-Rite)? Also, could the Kodak cal charts work as well in this application?

I'm sorry, but you have the money for an instrument, but not for the test chart? There really isn't a cheaper substitute.

--
-Stephen H. Westin
Any information or opinions in this message are mine: they do not represent the position of Cornell University or any of its sponsors.

Stephen H. Westin wrote:

RogM writes:

On 19 Dec 2003 14:43:44 GMT, (Bill Hilton)
wrote:

<snip>

It would be a good thing to be able to accurately reproduce the chart, especially since new ones are $80.

Well, you can't. Each patch is not only of a specific color, but has a specific spectral reflectance. If you managed to print one that is a perfect match to the real ColorChecker, it wouldn't be under different lighting conditions.

Does anyone have a workflow idea
for how to develop an ink/paper ICC profile by use of a color reflection densitometer (such as the Macbeth or X-Rite)? Also, could the Kodak cal charts work as well in this application?

I'm sorry, but you have the money for an instrument, but not for the test chart? There really isn't a cheaper substitute.

Actually, there is :-) The mini color checker is about $10 cheaper, and if you hover on eBay for a while you can find them for about $55. Which is another way of saying you can "rent" a color checker indefinitely for about $30 by selling it afterward on eBay

As for the Kodak cal charts, by which I assume you mean it8 targets or similar, probably yes, you can get a result that way, particularly if you stick to the gray step wedge. Things get problematical in a hurry, though, if you try to capture all the little patches of such a target using, say, www.curvemeister.com to sample each and every patch. The IT8 target was designed for scanner calibration, and does not really work well for a camera because of the subtle gradations.

If you want to experiment with this inexepensively, you may do so with curves instead of a profile. The free curvemeister demo will allow you to generate a curve based on assigning as many sample points as you like in RGB or Lab, save the sample points to a file with their color assignments. You may then generate a curve file in each color space reflecting your sample points.

Take care, and don't over-calibrate!

--

Mike Russell
www.curvemeister.com
www.geigy.2y.net