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Perils of color correction.Share your thoughts.

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  #11  
Old 09-12-2011, 01:56 PM
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Re: Perils of color correction.Share your thoughts

No worries John,

This is complex subject anyway. I suppose absolute means absolute in this case working in sRGB mode and choosing in info panel CMYK values. That is basically how I do correction in both CMYK and RGB values staying in sRGB color space.
I certainly need a book regarding this subject and thanks for the Andrew book tip.I will look into it after I finished with watching euro basketball game.
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  #12  
Old 09-12-2011, 03:09 PM
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Re: Perils of color correction.Share your thoughts

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Originally Posted by nebulaoperator View Post
I suppose absolute means absolute in this case working in sRGB mode and choosing in info panel CMYK values.
An absolute value would be Lab. Its based on how we see color. CMYK is based on some very specific output device (a printer, paper and colorants or inks). Adobe RGB and sRGB are based on a theoretical display. All CMYK and RGB devices are different although some are more similar than others. But Lab is absolute.

If you editing solely by numbers in sRGB and viewing numbers in some CMYK space, all you have to do is alter one (change to Adobe RGB (1998), alter the CMYK color settings) and both number sets will change. That’s not to useful. Lab will not suffer this condition. So if you want some way to look at color numbers in an absolute fashion, set the info palette to Lab for one readout, Actual Color for the other. That said, the scaling isn’t that intuitive but after using it awhile, you’ll get the idea.
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Old 09-12-2011, 03:28 PM
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Re: Perils of color correction.Share your thoughts

What I meant Andrew is info pallet as absolute in SRGB mode nut you can play in both in RGB or CMYK. In reference working on sRGB but lets say do color correction in CMYK.I don't quiet know if this makes the sense unless image goes for the print.Than why would one choose CMYK color correction from info in CMYK rather than RGB when image end up on the web?
When you say colors in absolute fashion and set the palette to LAB is this reading be absolute for the web and the print? Or I just buy your book and come back later?
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Old 09-12-2011, 03:37 PM
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Re: Perils of color correction.Share your thoughts

If you have an sRGB document and view Actual Color, you are viewing the numbers in sRGB. So in that context, its absolute. The conversion (in this case) to CMYK is really useless unless you intend to convert the sRGB document into CMYK for this process. That’s all the numbers are showing you. Unless you print the image to that device, the numbers are no more useful than any other color space or profile you could load to view said numbers (expect Lab). Lab is a device independent color space. Its not tied to this printer, that display etc. In this case, its an Absolute set of values that define a color based on human vision. If you have Lab values, you can produce ANY other set of values for any device you have a profile for.

The first question you need to ask is, why do I need these numbers? Do you want the numbers to be based on what you are actually currently working on or what the numbers will become if you alter the color space. If you only care about the current values, you only need to look at the actual color values. If you want to know what the numbers will become after you convert, based on where those numbers are going to be used, you can load that as well and get the conversion.

In this set of posts, CMYK is being loaded. Why I don’t know, especially when it appears no one intends to convert and print the sRGB file to that CMYK process. And we’ve seen where two people have different color settings and end up getting different CMYK values.

The $64K question is, why is anyone looking at CMYK values? Are you going to convert from sRGB to this exact profile to generate those numbers? And even if you are, is it useful or necessary to see the numbers while still in RGB?
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Old 09-12-2011, 04:01 PM
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Re: Perils of color correction.Share your thoughts

Lets say I only want images to be displayed on web. So it doesn't make a sense to work on the CMYK info pallet then, right?
Lets say if I work on LAB mode now are you saying this mode will be absolute for web, print or whatever as it is absolute?
Numbers? Hmm.. reference t oRGB mode numbers can give you indication what it should be less or more right but here I am confused when you can have a big shift in info pallet(sRGB lets say) and the color balance is right. When looking at one of your tiff looks like RGB values not necessarily have to be equal in value(less or more) to represent right color balance in image and the other images have pretty much tight values and the right color balance. Here I have confusion
Thanks Andrew.
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Old 09-12-2011, 04:41 PM
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Re: Perils of color correction.Share your thoughts

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Originally Posted by nebulaoperator View Post
Lets say I only want images to be displayed on web. So it doesn't make a sense to work on the CMYK info pallet then, right?
The World Wide Web (not a Web press)? None whatsoever.
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  #17  
Old 09-12-2011, 04:47 PM
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Re: Perils of color correction.Share your thoughts

Comment for Nebula and questions for Andrew

Quote:
Originally Posted by nebulaoperator View Post
Or I just buy your book and come back later?
Don't just come back later yet I would definitely recommend reading Andrew's book. All of the discussion around color managed workflow (including all of these posts) will make a lot more sense if you do.

Andrew, as per my added edit in a prior post and PM sent to you I want to give your approach a go. The approaches you mention make edits in ACR and Lightroom. That is where I do most of my initial edits though using RGB values to match up the color I want vs seeing LAB numbers (or even CMYK) is a pain in the rear for me. Is there a way to have the color samplers in ACR or Lightroom display numbers in LAB (or even CMYK) for adjustments?

I could probably get used to using RGB numbers in the above case of using ACR/Lightroom. However, I do have cases where I am doing my color adjustments in Photoshop. My question is do you have a link to the steps for making such color adjustments while in Photoshop. I can use similarly described techniques in prior posts in RGB and just monitor the Lab values in the info panel while making adjustments in the Curves Adjustment Layer. If there are productive techniques to do so while in LAB Color Mode I would be interested in a good pointer/link to the information. Thanks
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Old 09-12-2011, 07:20 PM
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Re: Perils of color correction.Share your thoughts

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Originally Posted by John Wheeler View Post
My question is do you have a link to the steps for making such color adjustments while in Photoshop. I can use similarly described techniques in prior posts in RGB and just monitor the Lab values in the info panel while making adjustments in the Curves Adjustment Layer. If there are productive techniques to do so while in LAB Color Mode I would be interested in a good pointer/link to the information. Thanks
Again, the question is, what do you guys feel the CMYK numbers are providing and what are you using to color correct while viewing such numbers? I have no idea what or why CMYK values based on something that will never be used can be a guide to anything. So I can’t answer your question. I know what RGB numbers provide when they are based on the RGB values I’m currently working with. I know what is a neutral. I know what defines clipping. In Lab I have a guide to what starts as good skin tones. Otherwise I use my eyes, view the image on a calibrated display and make the image appear as I desire knowing that once I soft proof, what I see is pretty close to what I’ll get.
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Old 09-13-2011, 12:39 AM
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Re: Perils of color correction.Share your thoughts

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Originally Posted by andrewrodney View Post

For Lightroom, percentages work as well (there is a pattern as seen here): http://digitaldog.net/files/LR_Skintone_Ratio.jpg
Thank you so much! Trying to get skin right is something I've found absolutely MADDENING in Lightroom. I really wish there was a LR option to get an eye dropper LAB color reading.

- Nancy
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  #20  
Old 09-13-2011, 03:04 AM
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Re: Perils of color correction.Share your thoughts

HI Andrew
Sorry if you felt that I had bypassed your question. I thought that was directed elsewhere. I am more than happy to give you my thoughts on that matter. Just as a reminder, I am interested in using the LAB numbers approach per my previous post and PM to you and just looking for the step by step tutorials since I am one of those folks that needs to start on training wheels. : )

Why have I used CMYK or more correctly the CMY values for skin tone adjustments:

- As long as I leave my default CMYK Working Space to the same specific Space (which I normally do and leave it set to US Web Coated (SWOP) v2), a specific value of CMYK as best as I can tell does not change in the color samplers / color picker independent of which RGB color space in which I am presently working. As an example, if I used your Lab value in one of your shared images (thanks) of the Caucasian woman of LAB= 63/21/20 those match with the CMY values of 22%/49%/56% for my fixed CMYK color space. If I Edit > Convert to Profile to any other RGB space those CMY values do not change while the RGB values significantly change. That gives me independence of the RGB color space changes (again as long as I am consistent with the CMYK color space I use)

- For values, with the Caucasian skin example, I adjust for Yellow values to the same or slightly higher than Magenta value and the Cyan about 1/2 to 1/3 of the Yellow/Magenta values as a starting point for the skin tone (Cyan sometimes needs to be lower). I noted that for the Working CMYK color space that I use for the initial CMY values that I target are in the same range as the Lab numbers in your TIF file. Then I adjust by sight on a calibrated monitor

- I use the Curves Adjustment Layer for the tuning. I set a color sample at what should be a mid tone skin area. Use the "finger tool" starting from that sample point. To adjust my Yellow value I use the Blue adjustment curve, then adjust the Cyan Values with the Red Curve. Since the CMY are not exactly opposite of RGB it takes two iterations and sometimes three for the initial adjustment. From there, I adjust to what looks right on the monitor. Using the RGB separate curves with the Curves Adjustment level tunes in the initial and fine tuning of the skin tone is quite easy and intuitive at least for me.

- I do not have to leave RGB working space with this procedure

- One of the downsides of this approach is that if I ever change the default CMYK working space (even for an experiment) and forget to change it back, the initial starting point numbers will be incorrect. That would not be an issue using LAB

In summary, I can use CMY values independent of RGB color space changes, I am used to what CMY values are needed in my default working space for good skin tones, I don't have to leave working in RGB, and I can use a pretty simple RGB Curves Adjustment Level to tune in the CMY values.

I hope that gives you some understanding of the whys of the approach I used in the past.

Now back to my questions if you have the time.

- I am looking for a step by step approach to tune in the skin tones with LAB values using Photoshop whether it be in RGB or LAB Working Space. Any pointers to those tutorials would be helpful.
- For Lightroom again thanks for the reference "percentage" RGB numbers. Do you know if Lightroom has any color sampler features (ala Photoshop or ACR) and also can one read LAB values instead of just percentage RGB (of whatever RGB Color Space that LR is using). That would sure make things a lot easier for me with your technique of Temp and Tint sliders. I have not been able to find those features so may need to just use the percentage RGB numbers for Lightroom.
- Similar question about ACR, it shows absolute RGB values instead of percentages. Good news it has color samplers yet being able to read in LAB would sure simplify things. Especially since the RGB numbers displayed in ACR are given in the Color Space set at the bottom of the ACR page (so the numbers you want depend on if you are going to Photoshop in sRGB, Adobe RGB, or ProPhoto RGB). If the Lab numbers are not available, it sounds like I would need to fix the targeted color space (e.g. to ProPhoto RGB) and use the absolute RGB scale.

Bottom line, I would prefer to use one consistent approach across Lightroom, ACR, and Photoshop at least for measurement if not also for procedure to make life simple. You will probably tell me that I am dreaming yet wanted to know what was possible.

Using a Lab based approach across Lightroom, ACR, and Photoshop is appealing to me for the consistency of an absolute Color Sapce.

Thanks again in advance for any additional advice.

And just to reiterate, I am not looking to debate the merits of one approach vs another, I just what more help in how to do this with LAB numbers as a reference.
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