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  #1  
Old 05-20-2006, 12:08 AM
extrememc extrememc is offline
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Gray Card

I have been having problem with setting the color balance using the gray card in CS2. I have attached to photos with and w/o the gray card and when I use the eye dropper in CS2 to adjust the color the results are not greats. What am I doing wrong? What I am trying to do is using the correct color balance for not only this photo, but a few other that were taking in this same location with the light the same. If someone could give me direction on this in lamen terms I would appreciate it. Thanks
Attached Images
File Type: jpg Joann gray.JPG (25.1 KB, 98 views)
File Type: jpg Joann.JPG (24.3 KB, 67 views)

Last edited by extrememc; 05-20-2006 at 12:16 AM.
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  #2  
Old 05-20-2006, 01:26 AM
Gary Richardson's Avatar
Gary Richardson Gary Richardson is offline
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Hi,

Don't have CS2, I use PS7, so not sure what tools you'll have that I don't.

OK, to use the grey card.

First use eyedropper sampler to put samplers on the mid grey, white, and black areas of the chart.

What you're wanting to do is get each of the values for R,G,B to be equal.

Start with mid grey as this is the major adjustment. Open a curves adj layer. Now look at the values for mid grey in your sampler. You're looking for which channel has the mid value. Now in curves open one of the other channels (in the drop down menu at the top of the box) move the curves cursor over your mid grey sampler point, and Ctrl+click. This will put a marker on your curves graph. Select that point, and move it up/down with the up/down keys on your keyboard to make the value of that channel equal to the value of the "mid value" channel. (look at the eyedropper values for mid grey as you adjust curves, the values to the right are the ones you're trying to equalise).

Now repeat this for the other channel.

You should now have equal channel values for the mid grey.

Next white. Here you want to make all the values equal to the largest value of the 3 channels. To achieve this use the same technique as described above.

Now black. Here you want to make all the channel values equal to the lowest value. Use same techniques again.

Lastly go back to mid grey. Altering the white and black points will have pulled your channel values a little. Select the mid value, and adjust the other channels to equalise. (usually it's easy to adjust).

Note: Usually you can't get all channels exactly equal in grey, white and black, just get the best balance you can. Mid grey is the most important to get balanced.

OOPS, have posted picture of eyedropper values before I made final mid grey adjustment, sorry. (But I think you can get the general idea from them).

Final picture is just to show what wierd shapes you can get in your curves when adjusting this way. I've showed the blue channel. White point to right, black (dark grey actually) to left.
Attached Images
File Type: jpg Joann gray CC.jpg (63.4 KB, 50 views)
File Type: jpg Eyedropper.jpg (9.0 KB, 20 views)
File Type: jpg Curves.jpg (29.6 KB, 17 views)

Last edited by Gary Richardson; 05-20-2006 at 02:07 AM.
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  #3  
Old 05-20-2006, 02:12 AM
imann08 imann08 is offline
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I essentially did the same thing as Gary did but used CMYK instead. That enabled me to look at her skin color and have a better idea of what I was doing. That's just a personal preference. Anyways, I put my markers on two of the grays, the skin of her chest and the left shoulder. I used the Curves Adjustment Layer. I control click on each of the markers starting with the grays and adjust them to get them to the proper numbers. Unlike RGB, with CMYK you want cyan to be just a little higher than magenta and yellow for a neutral color. I also nudged up the black channel to get a little more contrast.
Attached Images
File Type: jpg Joann-grayCMYK.jpg (73.2 KB, 36 views)
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  #4  
Old 05-20-2006, 05:32 AM
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Flora Flora is offline
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Hi,

....3 small Tips to add to Gary's great explanation ...

1) from Katrin Eismann's Book (and this is true for the Curves as well!!):
Quote:
To get the most out of Levels you will need to set the black and white target values before beginning. This tells Photoshop which values to use for black and white.

1. Open the Levels dialog box and double-click the white eyedropper. A Select white target color label appears above the color picker (see figure 2.9).

2. Use the HSB scale and set the white target color to 95% brightness, or RGB 243, 243, 243, and click OK.

3. Double-click the black eyedropper and set the black target color to 5% on the HSB scale, or 12, 12, 12 RGB, as seen in figure 2.10; click OK.

By setting the white target color to 95% you will hold slight tonality in your whitest whites, and the black target color 5% will hold shadow information in the darkest parts of the image.
2) Use a Levels/Curves Adjustment Layer instead of working directly on the image ....

3) .... this way, once you found the right values and you are happy with the result, you can simply 'drag and drop' your Levels/Curves Adjustment Layer to all other pictures taken in the same location and with the same light... Meaning ... you do the correction work only once ...

That's what I did with your pictures .. (Attachment 1)

* Working in RGB Mode, and using a Levels Adjustment Layer, I set White and Grey Points as shown in Attachment 2... (I didn't set the Black Point because I wasn't sure if any of the shadow in the image was really black)

* Dragged the Levels Adjustment Layer from the 'Grey Card' image I used to correct the colours and simply dropped it on top of the backgroung of the second image ...
Attached Images
File Type: jpg F_Joann-gray.jpg (99.2 KB, 65 views)
File Type: jpg W+G-Points.jpg (55.8 KB, 42 views)
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  #5  
Old 05-20-2006, 10:10 AM
Syd Syd is offline
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Flora, thanks for that excellent tip! I have been using Photoshop for almost a year and a half now I had no idea that you could set the values of the eyedroppers. Now I know why everything went dazzingly white when I touched it with the white eyedropper. To remedy that I have always just turned down the opacity of the adjustment layer (perhaps with the same results, I'm not sure...) but this way I can now set those values as default values. Thanks again.
Sincerely Syd
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  #6  
Old 05-20-2006, 10:31 AM
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byRo byRo is offline
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The geek way......

The question has already been superbly answered - so I'll go off on a little tangent now.

Hey, wait a minute - a thread about colour correction and nobody has mentioned LAB mode?

There is, actually, a good reason for not using LAB mode here.
In LAB the colours and the luminosity are separate entities.
This way any adjustments made to the colours will apply equally to all luminosities - which is usually what we want.

In this case however, extrememc, has been thoughtful enough to provide us with grey references at various different luminosities. A quick fix in LAB gets them all pretty close to 0 for the A and B values - but not all at the same time.

OK, so forget LAB and let's stay with RGB (or C,M,Y,K ).
Adjusting colours in RGB has a drawback that many often forget. If we mess around with the R,G,B values without taking the necessary precautions we may correct the colour but we are going to alter the Luminosity.

So here's a geek way.......
1) Drop four eye-dropper points,one for each grey reference;
2) In the info palette (<F8>) change the readings from RGB (default) to LAB (Aha!! );
3) Make a curves adjustment layer and click on each of the 4 eye-dropper points in turn with <CTRL> and <SHIFT> pressed (this makes marks on the curves for R,G and B at the same time )
4) Play time Watch the info palette and move the points on the R,G,B curves until the A and B values get to zero (grey) and the L value is unchanged.

After having fixed the four points you'll see that the curves (especially Red) may be stretching at the end points - move the end point to straighten out the curve.

There you have it - one "perfect" geek adjustment.

Overkill? Yes
Interesting? Well I thought so.

Attached Images
File Type: jpg GreyCard-byRo.jpg (99.3 KB, 52 views)
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  #7  
Old 05-20-2006, 12:38 PM
Syd Syd is offline
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Ro, thanks for that detailed and clear description. I can't set my color sampler points to show Lab values when in RGB mode. My info options palette gives me three options: First Color Readout, Second Color Readout and Mouse coordinates. No matter what combination I set them in, as long as I am in RGB they only show RGB values. I have included a screen shot to show what I mean. Secondly you point out that changing color in RGB mode can mess with the luminosity. What if you used levels or curves to change the color (say by using the grey eyedropper tool) and then set the adjustment layer to color. Would that be the same as changing the color in Lab?
Sincerely Syd
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File Type: jpg Query.jpg (90.2 KB, 13 views)
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  #8  
Old 05-20-2006, 01:16 PM
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Cameraken Cameraken is offline
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Hi Extrememc.

A few more points.

This is one big grey card. It also looks homemade. That’s OK but the grey need to be 18% reflective to be a ‘mid’ grey. If this is not the case then it can’t really be relied upon for exposure. (Although it will work fine for colour balance)

Because the grey card is so big it could be affecting exposure.
If you are using TTL metering this large grey card in the middle of the picture could be altering the exposure (especially if it’s shiny)
This would mean that the black on the greycard would not be the blackest point in the image.

Had the greycard been hung on the background I think your results would be improved.
The black on the greycard could be guaranteed as the darkest black in the picture (because it’s farthest away from the light source)

I tried to colour correct the second image without the greycard. I knew the background should be white and the hair black, then I added a curve to boost the midtones.


Ken.
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File Type: jpg Ken_Joann.jpg (78.1 KB, 33 views)
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  #9  
Old 05-20-2006, 01:35 PM
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byRo byRo is offline
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Quote:
Originally Posted by Syd
Ro, thanks for that detailed and clear description. I can't set my color sampler points to show Lab values when in RGB mode.
Have a look at the arrow in my attachment. It points to a little triangle. Click on the triangle and a menu pops out with ALL the options. (You set each point separately)

Quote:
Originally Posted by Syd
What if you used levels or curves to change the color (say by using the grey eyedropper tool) and then set the adjustment layer to color. Would that be the same as changing the color in Lab?
Sincerely Syd
Like I said my method is a sort of illustrative overkill.
Yes, you would get practically the same results.

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  #10  
Old 05-20-2006, 08:56 PM
Syd Syd is offline
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Ro, got it. That's two things you have taught me today. I had no idea you could do that. They don't even look like they are clickable! And thanks for the tip about shift-ctrl clicking the eye-dropper points. It puts all the points on the R,G and B curves simultaneously. What a time saver! Flora's tip about setting the values for the black and white eye-droppers is a great one too. You guys are really so helpful.

Sincerely Syd
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