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ICC false profiles for color grading/correction

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  #41  
Old 02-11-2017, 02:16 PM
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andrewrodney andrewrodney is offline
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Re: ICC false profiles for color grading/correctio

Device Link Profiles and CMYK-to-CMYK Conversions: Sometimes, the ability to convert from an original file from RGB to CMYK isn’t possible. If an existing CMYK document exists but it needs to be reseparated into a new flavor of CMYK, there are a several issues to consider. One potential problem with CMYK-to-CMYK conversions is that the black generation can change since the conversion is from CMYK to PCS (CIELAB) then back to CMYK. This will affect solid black items like text or drop shadows that were intended to print with only black ink. A new mix of CMY and K inks will be used instead of just black ink.

One method that is a solution to this problem is to use a type of ICC profile called a device link. A device link is like two profiles hardwired into one. There is no Source and Destination methodology with device links because they are built as a one-way street, allowing only a very specific, fixed type of conversion. Products that build device links first ask the user which two profiles they wish to use and the order in which the transformation should take place. If I specify I want a device link to be built with the US U.S. Web Coated (SWOP) v2 profile as the source and the U.S. Web Coated profile as the destination, this is the order of the CMYK-to-CMYK con- versions. No PCS enters the picture and it’s possible to produce a better CMYK-to-CMYK con- version with more control over the remapping of the black channel.
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  #42  
Old 02-11-2017, 02:18 PM
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Re: ICC false profiles for color grading/correctio

Quote:
Originally Posted by Shoku View Post
Regarding data:

The first three attached images show the levels for each image in the profile adjustment sequence - no white lines means no data loss, even though the shape of the levels is slightly different due to the conversion.

The fourth image shows the levels after a curves adjustment and the obvious data loss.
The data loss will occur once converted but in high bit, it's moot! The same is true using a Photoshop curve or other such adjustment. There is no free lunch here! But the check for the lunch isn't pertinent when we edit in high bit, which we should always do IF we are worried about data loss (and white lines in a Histogram).
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  #43  
Old 02-11-2017, 03:35 PM
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Tony W Tony W is offline
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Re: ICC false profiles for color grading/correctio

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Originally Posted by Shoku View Post
... I use gamma adjusted profiles to apply a density change without adversely changing the color, for a quick adjustment when I know the client is seeing the image lighter or darker on their end because of bad calibration....
Different strokes for different folks I guess but I would not bother adjusting the profile gamma but may use the Exposure tab to affect gamma only.

I would certainly not send out a gamma adjusted file, or in fact any adjusted image just trying to compensate for a clients bad calibration. I would rather try and educate the client with some basic images and a description of how they should look maybe including one of the test images or a series of tests such as Lagom.

I can just envisage the scenario I send out a poorly corrected image to a client to compensate for either my guess of where their monitor is at or even visit to see how bad it is and apply a crap correction to compensate. Said client then decides to send out to a lab for a print or two and is horrified with the returned result- lab blames image data, client blames me

The changes to the histogram are largely due IMO to pushing data in 8 bit. The fact that you have got data loss in certain areas plain to see but so is the fact that the push has also added data in other areas hence the single spikes appearing above areas which were previously smooth.

If I need to change gamma I would tend to use the Exposure control using the Gamma slider only without profile jumping. AFAIK causing the same 'damage' as profile jumping. This is only a one click solution although the sliders has the advantage of infinite adjustment within the normal limits in addition it is possible to use presets.

Attached image show data from raw output from ACR as Prophoto with the duplicate image having adjustment to gamma only - no sign of data loss in the histogram.
Second image convert to Adobe RGB then duplicated and applied a gamma of 1.0 approximately i.e. gamma slider set to 2. Again other than histogram shape nothing bad
Attached Images
File Type: jpg Prophoto-with-exposure-gamma-change.jpg (158.1 KB, 6 views)
File Type: jpg AdobeRGB_AdobeRGBGamma1.jpg (159.2 KB, 10 views)
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  #44  
Old 02-11-2017, 04:12 PM
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Re: ICC false profiles for color grading/correctio

Is anyone with Photoshop CS6 kind enough to load this LUT (https://www.sendspace.com/file/einwcq) in a color lookup layer, in lab mode, and then export it as an ICC abstract profile just to see what happens?

Thanks
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  #45  
Old 02-11-2017, 04:25 PM
SZStudio SZStudio is offline
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Re: ICC false profiles for color grading/correctio

What the problem?
Just load the LUT in Color Lookup layer, do not flatten, and export as Device Link profile
File> Export> Color Lookup tables> ICC profile

You can't save as Abstract in Photoshop (cause the layers will be flattened)
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  #46  
Old 02-11-2017, 04:53 PM
klev klev is offline
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Re: ICC false profiles for color grading/correctio

I usually don't load random things, but I checked it using a text editor. I have CS6, but I don't see a way to do this. File > export doesn't contain that option.
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  #47  
Old 02-11-2017, 05:04 PM
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Re: ICC false profiles for color grading/correctio

Quote:
Originally Posted by SZStudio View Post
What the problem?
I am on CS5.

Quote:
Originally Posted by klev View Post
I usually don't load random things, but I checked it using a text editor. I have CS6, but I don't see a way to do this. File > export doesn't contain that option.
Photoshop can export abstract profiles only if you are in Lab mode.
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  #48  
Old 02-11-2017, 05:31 PM
klev klev is offline
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Re: ICC false profiles for color grading/correctio

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Originally Posted by marameo View Post
Photoshop can export abstract profiles only if you are in Lab mode.
It still doesn't show up, and I can't load a cube in Lab mode for obvious reasons. Converting to lab would simply delete that cube. I mean converting to lab would either flatten the image or discard the color lookup layer. I don't think this is a supported workflow in photoshop or at least not CS6. Even in Lab mode, it didn't show up under my export menu.
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  #49  
Old 02-12-2017, 10:20 AM
Shoku Shoku is offline
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Re: ICC false profiles for color grading/correctio

Quote:
Originally Posted by Tony W View Post
I would rather try and educate the client with some basic images and a description of how they should look maybe including one of the test images or a series of tests such as Lagom.
We do that, almost every day. With an average of 600 clients a week, and fast turn-around times (one day in some cases), there is often not enough time for the client to re-submit their files. And to complicate the issue of bad files, most of those who submit files that need this type of correction know nothing about Color Management or Monitor Calibration, and it's not always that easy to teach someone over the phone or via email who is clueless, and frankly, just not that interested. A common response: "You're the experts, you fix it."

I think the failure here by some members to accept the concepts I have presented is a lack of understanding that this particular process is not used every day, but just one tool that's used as needed, like every other tool in PS.

We are open to advice, as long as that advice is not demeaning in it's presentation, with the understanding that, like most adjustments, there are often multiple ways to achieve the same result.

With the altered profiles already created, assigning when needed is quick , simple and works.

Quote:
Originally Posted by Tony W View Post
I can just envisage the scenario I send out a poorly corrected image to a client to compensate for either my guess of where their monitor is at or even visit to see how bad it is and apply a crap correction to compensate. Said client then decides to send out to a lab for a print or two and is horrified with the returned result- lab blames image data, client blames me
We do not guess or apply crap corrections. We are an offset printing facility. Two offset Komori presses on one HP Digital Press. We correct files for clients, but the majority of our corrections are to prepare files to print based on client instructions or to match submitted printed samples. When the printed sample is lighter or darker than the file we immediately notify the client and proceed based on knowledge, not assumption.
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  #50  
Old 02-12-2017, 11:00 AM
Shoku Shoku is offline
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Re: ICC false profiles for color grading/correctio

Quote:
Originally Posted by Tony W View Post
The changes to the histogram are largely due IMO to pushing data in 8 bit.
Exactly. When you receive an 8 bit file, changing to 16bit really doesn't help much.

Sample 1 Curve adjustment in 16bit.
Sample 2 Assign Profile in 16bit
Attached Images
File Type: png 16_curves.PNG (187.7 KB, 4 views)
File Type: png assing_16.PNG (187.2 KB, 4 views)
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