Correcting colour using Curves and Gretag Macbeth CC

D
Posted By
Dinarius
Jul 21, 2006
Views
705
Replies
6
Status
Closed
I had been using a Levels Layer to correct colour by taking samples with the Colour Sampler Tool from four of the grey scale patches on the Gretag CC and then adjusting the channels individually.

Someone suggested that I should try a Curves Layer instead. I did and the results are astonishing. In Levels, when it got to the fine tuning stage in each channel, the R/G/B levels in one sample started to affect those in another. However, in Curves this doesn’t seem to happen. So, the tonal range is noticably greater and the colour is a lot more accurate. (I shoot mostly fine art for catalogue.)

However, the Colour Sampler Tool only allows me to take four samples and there are six grey scale patches on the Gretag CC. I’d like to be able to use all of them.

What is the best way of doing this?

Many thanks.

Denis

Must-have mockup pack for every graphic designer 🔥🔥🔥

Easy-to-use drag-n-drop Photoshop scene creator with more than 2800 items.

D
Dinarius
Jul 21, 2006
One other question……..

On the point of the actual RGB values of each of the Gretag CC patches……and I realize that this may be outside the remit of this forum.

There seems to be little agreement of what the actual values are.

Bruce Lindbloom argues here > <http://www.brucelindbloom.com/> (click on Calc/ColourChecker RGB summaries…..) that the values are colour space dependent.

I have done tests, all in ARGB 1998, using four of the six grey scale patches and inputting the values given by Lindbloom, Gretag and Fraser. There differences in the actual input values are subtle. But, the results are noticalbly different. On my calibrated monitor, Lindbloom’s values produce the cleanest results.

I would be interested in anyone’s recommendations for choice of colour space and corresponding Gretag CC grey scale input values.

Many thanks.

Denis
M
mm
Jul 22, 2006
Denis
The best info for the color checker chart is below and has every combination. <http://www.babelcolor.com/download/RGB> Coordinates of the Macbeth ColorChecker.pdf Malcolm
D
Dinarius
Jul 22, 2006
Malcolm,

Outstanding! Just what I was looking for.

By the way, the link you posted is no longer working.

This is the new one…..

<http://www.babelcolor.com/main_level/ColorChecker.htm>

Many, many thanks.

Denis
D
Dinarius
Jul 22, 2006
Or more directly this link…….

< http://www.babelcolor.com/download/RGB%20Coordinates%20of%20 the%20Macbeth%20ColorChecker.pdf>

Scroll down to page 5.

D.
D
Dinarius
Sep 4, 2006
Philo,

After a lot of experimentation over the last few weeks, I’ve come to the conclusion that Hue/Sat is the only way to go.

I’ve used the following workflow to very good effect.

Shoot the Gretag CC.

Using Adjust tab in ACR, adjust the six grey patches until they are as close as possible to readings I want (Babelcolor 16bit A1998).

Using the Calibrate tab, adjust until the RGB patches are as close as possible – paying particular attention to getting the three colours correct in each of their own patches (e.g. getting the red in the red patch to 152)

Save these settings and apply them to all the other images.

Process the shot of the Gretag CC.

Then in CS2…………

Using a Levels Layer. Adjust the White, 4th Grey Patch (160, 160, 160) and Black pathces to the required levels.

Using a Hue/Sat Layer. Fine tune the Red, Green, Blue and Yellow patches until they’re where I want them. In fact, the only reading I can’t get pretty much bang on is the blue in the Yellow patch. Getting a reading of 7 when it should be 53. All 11 other readings are within +/- three points.

I then simply Save and Load these settings to the other images.

Results are superb, I have to say. The HS just takes a bit of getting used to, but it’s far more accurate than Selective Color Adjustment Layer.

Thanks for your help.

D.
SS
Steve_Snow
Sep 24, 2006
While I am familiar with the strategies and techniques described above, I would like to get even more "objective" color accuracy with RAW images.

I want to shoot the image (metered for "perfect" incident exposure), run it through ACR, and the apply software (like Gretag macbeth profile Maker) to create a profile thta can be applied for all shots taken under identical lighting conditions. Exact representational color accuracy is critical for the these images.

Unfortunately, the adjustment tabs for exposure, brightness and contrast are completely arbitrary and seemingly MUST be applied to the image before getting it into CS2. I am completely unclear on what "neutral settings" are. "25" for brightness?? "50" for contrast?? How do I get the CC image out of ACR with minimal alteration while maintaining the perfect lighting for the exposre so it can be accurately and appropriately analyzed by a profiling software?

Thanks for your help.

Steve Snow

Must-have mockup pack for every graphic designer 🔥🔥🔥

Easy-to-use drag-n-drop Photoshop scene creator with more than 2800 items.

Related Discussion Topics

Nice and short text about related topics in discussion sections