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How to remove annoying magenta cast

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  #21  
Old 11-22-2010, 04:25 PM
fashionbug fashionbug is offline
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Re: How to remove annoying magenta cast

Quote:
Originally Posted by Mike Needham View Post
What I don't much understand is why there is so much guesswork going on. If in any doubt at all you could correct by the numbers, but otherwise..... I'm more of the mind of Flashtones in saying that finding the neutral will sort most of your cast out.

What do you mean by that ?

done some further corrections :

What do you think, is the color balance off the scale :

http://fashionbug.org.uk/color_corre..._red_scarf.jpg
http://fashionbug.org.uk/color_corre...red_scarf2.jpg
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  #22  
Old 11-22-2010, 04:35 PM
fashionbug fashionbug is offline
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Re: How to remove annoying magenta cast

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Originally Posted by pavkey88 View Post
lots of variations here. Makes me think the color settings for the monitors are in need of adjustment. Tareq's seem to be the most accurate to me - I just calibrated a week ago.

Like Mike said, if in doubt go by the numbers. Everybody's eyes play tricks on them once in a while.
What do you mean by go by the number ?
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  #23  
Old 11-22-2010, 05:15 PM
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andrewrodney andrewrodney is offline
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Re: How to remove annoying magenta cast

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Originally Posted by fashionbug View Post
What do you mean by go by the number ?
Good question. A lot of work by the numbers indeed is effective, some not at all.

IF you are dealing with RGB in an RGB working space (sRGB, Adobe RGB (1998), ColorMatch RGB, ProPhoto etc), then when all three values are equal, its neutral. 67/67/67, 129/129/129 etc. This is not necessarily true in all RGB color spaces but IS in all RGB working spaces. So if you can get that gray bkgnd to be three identical (or very close) values, and indeed it or something else in the image is a known neutral, fixing that cast will often pull the other colors in line.

There is an old urban legend of working by the numbers in CMYK (usually presented for skin tone values) that really needs to die and go away because CMYK is a highly device dependent color space based on some mix of inks for some kind of press. In the very old days, when Photoshop had a fixed definition of CMYK for one device, people were able to work by the numbers after a lot of testing and playing around. But any modern version of Photoshop (past say version 5) can deal with a myriad of CMYK device color spaces such that a set of values someone gives my be OK and may be a mile off.

Working by the numbers and using a well calibrated and profiled display is useful, but only when the colorspace of the document is in a condition where the numbers are well defined. That is the case with RGB working spaces in terms of neutrals, and neutrals are one area where you can often look and correct for a color cast. I say usually because gray cement, lit by sunset should not be neutral, it should have a golden glow. All this work by numbers stuff needs some human intervention!
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  #24  
Old 11-22-2010, 05:32 PM
fashionbug fashionbug is offline
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Re: How to remove annoying magenta cast

i tried to get that gray bkgnd to be three identical, but somehow cannot manage to do that.
am i doing something wrong ?
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  #25  
Old 11-22-2010, 05:38 PM
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andrewrodney andrewrodney is offline
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Re: How to remove annoying magenta cast

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Originally Posted by fashionbug View Post
i tried to get that gray bkgnd to be three identical, but somehow cannot manage to do that.
am i doing something wrong ?
I’d do it in my raw converter (ACR or Lightroom) using the WB eye dropper (on a highlight I want neutral). In Photoshop you can set the grays neutral using the gray eyedropper tool in Levels or Curves. But be careful what you first set for the eyedropper sampling size. Click on the Eyedropper tool in the tool bar first. Check the sampling in the options bar (1x1, 5x5 etc). If set incorrectly, when you then use the eyedropper tool in Levels or Curves, it will use that toolbar eyedropper for the sampling. If it were set to say 100x100 and you didn’t get just the gray bkgnd, the results would be hosed.
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  #26  
Old 11-22-2010, 07:33 PM
SilvaFox SilvaFox is offline
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Re: How to remove annoying magenta cast

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Originally Posted by fashionbug View Post
What do you mean by go by the number ?
Hey Bug,

A lot of people would correct this cast by displaying CMYK "numbers" in the info palette and by using curves in an adjustment layer, would pull back on the magenta until it was 5 (or so) percentage points behind the yellow.

Your monitor can be green, orange or purple and those numbers won't change.

Sincerely,

Urban Legend

PS, Make sure to change the default "point sample" on your eyedropper to 3x3 or 5x5 as per Mr. Rodney, or you'll be getting a zillion different readings.
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  #27  
Old 11-22-2010, 11:09 PM
Tareq Tareq is offline
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Re: How to remove annoying magenta cast

I can get the most accurate color shots if i do more steps, but if one smaller size posted shot here and asked to correct it then even we can do something but i feel it will not be the best accurate work to do, i have calibrated monitors and i work on 30" monitor now even it is not the best but i can see the cast and i can't work great on that small JPEG pic, always the RAW and larger sizes will make it easier to go more accurate, and honestly speaking, my Hasselblad camera rendering the color way better than my Canon cameras, when i compare both shots done at same exact lighting condition i feel that Hasselblad shots colors are more natural and truer than Canon DSLRs shots.
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  #28  
Old 11-23-2010, 02:09 AM
fashionbug fashionbug is offline
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Re: How to remove annoying magenta cast

Quote:
Originally Posted by andrewrodney View Post
I’d do it in my raw converter (ACR or Lightroom) using the WB eye dropper (on a highlight I want neutral). In Photoshop you can set the grays neutral using the gray eyedropper tool in Levels or Curves. But be careful what you first set for the eyedropper sampling size. Click on the Eyedropper tool in the tool bar first. Check the sampling in the options bar (1x1, 5x5 etc). If set incorrectly, when you then use the eyedropper tool in Levels or Curves, it will use that toolbar eyedropper for the sampling. If it were set to say 100x100 and you didn’t get just the gray bkgnd, the results would be hosed.
Not sure i understand correctly.
is it in this window below that the settings for the eyeddroper have to be set to 1x1, 5x5, etc ?
http://livedocs.adobe.com/en_US/Phot...ages/ct_16.png

Last edited by fashionbug; 11-23-2010 at 03:28 AM.
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  #29  
Old 11-23-2010, 07:16 AM
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mistermonday mistermonday is offline
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Re: How to remove annoying magenta cast

Fashionbug, no, not there. You select the Eyedropper tool from the toolbar. Then look near the top left on your monitor - the Option Bar running across the screen. The pull down menu let's you select the sampler size: point sample, 3x3, 5x5 etc. I would attach ascreenshot but I am on my iPhone now.
Regards, Murray
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  #30  
Old 11-23-2010, 08:18 AM
Byakuya Byakuya is offline
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Re: How to remove annoying magenta cast

Quote:
Originally Posted by andrewrodney View Post
Good question. A lot of work by the numbers indeed is effective, some not at all.

IF you are dealing with RGB in an RGB working space (sRGB, Adobe RGB (1998), ColorMatch RGB, ProPhoto etc), then when all three values are equal, its neutral. 67/67/67, 129/129/129 etc. This is not necessarily true in all RGB color spaces but IS in all RGB working spaces. So if you can get that gray bkgnd to be three identical (or very close) values, and indeed it or something else in the image is a known neutral, fixing that cast will often pull the other colors in line.

There is an old urban legend of working by the numbers in CMYK (usually presented for skin tone values) that really needs to die and go away because CMYK is a highly device dependent color space based on some mix of inks for some kind of press. In the very old days, when Photoshop had a fixed definition of CMYK for one device, people were able to work by the numbers after a lot of testing and playing around. But any modern version of Photoshop (past say version 5) can deal with a myriad of CMYK device color spaces such that a set of values someone gives my be OK and may be a mile off.

Working by the numbers and using a well calibrated and profiled display is useful, but only when the colorspace of the document is in a condition where the numbers are well defined. That is the case with RGB working spaces in terms of neutrals, and neutrals are one area where you can often look and correct for a color cast. I say usually because gray cement, lit by sunset should not be neutral, it should have a golden glow. All this work by numbers stuff needs some human intervention!

I agree. that should solve the problem
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