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Photo Retouching "Improving" photos, post-production, correction, etc.

Color correction

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  #1  
Old 07-27-2010, 05:00 PM
Caravaggio Caravaggio is offline
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Color correction

Hello,

I am trying to learn how to do more accurate less subjective color correction on product shots as I have been told that my work has too many color casts in the grey and shadow areas of my images.

I can't seem to find any neutral greys in my image by using a neutral grey layer set to difference. (Greys should be 0,0,0 in RGB when the grey layer is set to difference, right?) What I have been doing instead is turning off the neutral grey layer and taking color samples of the areas that I think should be grey. I am then balancing the sampled points in curves so that each RGB channel has the same or close numbers for any sampled point. Is this how one balances the channels to remove a color cast or are there better ways? Oh one final question, should the curves adjustment layer on which the greys are being balanced be set to color as I don't want to alter the luminosity of the image?

Thanks a lot.
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  #2  
Old 07-27-2010, 06:56 PM
madclark madclark is offline
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Re: Color correction

It's really too easy for your eye to be fooled. I'd highly recommend you invest in a colorometer and use it. EyeOne or Pantone make a couple different models. The Huey II is a great starter model. It's just too difficult to calibrate with the naked eye. The method you use is to remove color cast should be considered a fix more than workflow.
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Old 07-27-2010, 07:07 PM
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0lBaldy 0lBaldy is offline
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Re: Color correction

after you get your 50% gray layer set to difference do a threshold adjustment layer.... slide the slider to the left till there is a small black point just large enough to accommodate the bullseye of the eyedropper tool that shows up and after you hold down the Shift key and click to set the point ( that is the neutral gray point.... you could then turn off the 50% Gray layer and use the same threshold layer again to establish and set the white point by sliding the slider to the right till you just see a white area just big enough for the bullseye (beware of reflections though) .. then set the black point the same way by going left..

when all three points are set hide the threshold layer and open a curves or levels adjustment layer and use those points to set the white, gray, black points

hope this helps some
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Old 07-27-2010, 07:33 PM
Caravaggio Caravaggio is offline
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Re: Color correction

I am on a calibrated monitor using color monkie.

That was really helpful, Olbaldy. I managed to find something very close to the grey point using your method. Thanks.
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Old 07-27-2010, 07:45 PM
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andrewrodney andrewrodney is offline
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Re: Color correction

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Originally Posted by Caravaggio View Post
I am on a calibrated monitor using color monkie.
Its an excellent solution. If you also want to work numerically, keep in mind that all RGB working spaces are well behaved, meaning that when R=G=B, the color is neutral (no cast). 20/20/20, 165/165/165, any three identical RGB values are a neutral. Be sure to set the eyedropper sampler appropriately (often more than 1x1). The set gray eyedropper in level and curves, in fact ALL eyedroppers though out the app use the eyedropper sampling you set in the options pane to sample color.
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Old 07-27-2010, 09:03 PM
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Aladdin Aladdin is offline
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Re: Color correction

Gentlemen, what do you think of this trick I learned a while ago to achieve almost same outcome:
Image/Adjustment/Matchcolor and the only thing you do is to "check" Neutralize box, this method works for most of the time.
I really like to know what the experts here think of it? Any downon side to it? Thanks
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Old 07-27-2010, 10:43 PM
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TommyO TommyO is offline
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Re: Color correction

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Originally Posted by Caravaggio View Post
I have been told that my work has too many color casts in the grey and shadow areas of my images.
Caravaggio,

With regard to color casts in the shadows, a common means of correcting these is to mask the shadows, convert to CMYK and desaturate the CMY channels. (It's simply faster and more exact.) While color casts look normal in the real world in reflections, etc, they generally are not acceptable in shadows for product shots (as was pointed out to you). I believe this same topic was covered in one of the jewelry RetouchPro Live broadcasts from Steve Koshlap. You may want to search the site for the link to the rebroadcast that Doug makes available on Youtube and give it a look.
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Old 07-28-2010, 10:58 AM
Caravaggio Caravaggio is offline
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Re: Color correction

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With regard to color casts in the shadows, a common means of correcting these is to mask the shadows, convert to CMYK and desaturate the CMY channels.
Tommy,

It sounds like a great technique, but I am wondering how to perform a channel by channel desaturation in CMYK. I converted the image to CMYK, masked the shadows and then chose one of the CMY channels. I then went to image adjustments, but hue saturation was not an option as it was grayed out. What am I doing wrong? Thanks.
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  #9  
Old 07-28-2010, 11:12 AM
Caravaggio Caravaggio is offline
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Re: Color correction

Oh, never mind, Tommy, I solved it! I see that I have to do the channel by channel desaturation as an adjustment layer when in a CMYK workspace.
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  #10  
Old 07-28-2010, 11:17 AM
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andrewrodney andrewrodney is offline
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Re: Color correction

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Originally Posted by Caravaggio View Post
Tommy,

It sounds like a great technique, but I am wondering how to perform a channel by channel desaturation in CMYK.
Not at all a good idea to convert from RGB to CMYK for this kind of work (or for that matter, anything but preparing this document for output to the said CMYK device). Huge data loss in terms of color gamut, time lost and so forth (more about this Saturday if you want to know more).
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