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ICC false profiles for color grading/correction

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  #31  
Old 02-11-2017, 03:10 AM
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Re: ICC false profiles for color grading/correctio

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Originally Posted by klev View Post
Most of the time there isn't much of an advantage in applying something in LAB. People do it when the correlation of RGB channels is problematic, but they don't do it using ICC profiles.
This might be worth pointing out: "Abstract profiles" are ALWAYS Lab to Lab profiles (independent color values e.g. Lab/XYZ inside) whereas usual ICC profiles (sRGB.icc etc..) are the connection between device dependent color space (RGB, CMYK) and device independent color space (Lab, XYZ). Abstract profile maps the original Lab values to the corrected Lab values.

"Device Link profile" is the connection profile between device dependent color spaces (RGB to RGB) without connecting to the device independent color space (Lab, XYZ).

Photoshop will convert from RGB to Lab and back again to RGB when Abstract profile is use.

So, the goal is to create an abstract profile to change the appearence of the image by tweaking the Lab colors without altering the RGB values.
Attached Images
File Type: png abstract profile2.PNG (57.2 KB, 9 views)
File Type: png usual_profile.PNG (22.4 KB, 5 views)

Last edited by marameo; 02-11-2017 at 03:24 AM.
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  #32  
Old 02-11-2017, 03:49 AM
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Re: ICC false profiles for color grading/correctio

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Originally Posted by marameo View Post
So, the goal is to create an abstract profile to change the appearence of the image by tweaking the Lab colors without altering the RGB values.
This does not sound possible, perhaps a language translation issue but...

If you 'tweak' the L*a*b* colours by altering values as you must, then the RGB values must also change. If it was possible the RGB values remaining the same equals no change in image appearance.

Apart from a plugin making things easier I.e. A one click solution, I have yet to see any advantage to applying a wrong profile (probably more accurate than declaring it a false profile). Sure you will/may dramatically alter the image appearance in assigning a wrong profile but this is what you would probably do more elegantly using the tools provided in PS. BTW wrong profile is probably just as silly as calling a false profile, and if you create your own profile perhaps it should be called strange profile or mystery meat profile who knows

The underlying original image data is fixed at the time of acquisition but can be pushed and pulled in so many ways with so many tools I am having a hard time understanding why and how a particular method is preferred.

I will be very happy to have my knowledge extended and my thoughts corrected but PLEASE do not just waffle on theorising. Please provide image examples and methodology to corroborate your findings
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  #33  
Old 02-11-2017, 06:12 AM
SZStudio SZStudio is offline
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Re: ICC false profiles for color grading/correctio

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Originally Posted by klev View Post
Ultimately people do nonsense like this when they're trying to work around a very bad design (and yeah ICC profiles have a very ugly design)
Are you sure?
Device link and Abstract are just the color correction tools, like curves or shadow/highlights, you can use the Masks, Blend If of the Layer, change the Blend Modes etc.
But the result depends of the color space of the image, sRGB, EktaSpace, ProPhoto etc.

Think different, color correction profiles are huge time savers, you can get the effect in one second, here is an example:
Technicolor Process 4 - 3 Strip
Attached Images
File Type: jpg BA.jpg (66.9 KB, 12 views)
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  #34  
Old 02-11-2017, 06:31 AM
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Re: ICC false profiles for color grading/correctio

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Originally Posted by Tony W View Post
If you 'tweak' the L*a*b* colours by altering values as you must, then the RGB values must also change. If it was possible the RGB values remaining the same equals no change in image appearance.
Of course the RGB values must also change; let the CMM (PCS) deal with that.
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  #35  
Old 02-11-2017, 08:36 AM
Shoku Shoku is offline
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Re: ICC false profiles for color grading/correctio

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Originally Posted by SZStudio View Post
Are you sure?
Device link and Abstract are just the color correction tools, like curves or shadow/highlights, you can use the Masks, Blend If of the Layer, change the Blend Modes etc.
But the result depends of the color space of the image, sRGB, EktaSpace, ProPhoto etc.

Think different, color correction profiles are huge time savers, you can get the effect in one second, here is an example:
Technicolor Process 4 - 3 Strip
Exactly my point regarding gamma changes. Same color space for both sample images. One with a gamma of 2.2 (CM_1) and the other with a gamma of 1.8 (CM_2) to bring it back to what was originally intend, then converted to the final output color space.
Attached Images
File Type: jpg CM_1.jpg (464.0 KB, 9 views)
File Type: jpg CM_2.jpg (474.7 KB, 9 views)
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  #36  
Old 02-11-2017, 09:57 AM
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Re: ICC false profiles for color grading/correctio

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Originally Posted by Shoku View Post
Exactly my point regarding gamma changes. Same color space for both sample images. One with a gamma of 2.2 (CM_1) and the other with a gamma of 1.8 (CM_2) to bring it back to what was originally intend, then converted to the final output color space.
Still not getting this. You assign a profile with a lower or higher gamma than the original to attempt to enhance or bring back detail contained in the original data making the image look good then you convert to required output space.

Why, when you can adjust gamma in PS by at least a couple of methods without assigning wrong profiles then converting to bring back into line?

It seems to me that it should be preferable most of the time to use PS tools direct to adjust gamma on the fly with the advantages of both visual clues and the ability to have seamless control of the steps rather than jumping from say gamma 1.0, 1.8, 2.2 etc.

Unless th point is that you know you have received a file that is incorrectly tagged then it seems the proper time to assign the correct profile.
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  #37  
Old 02-11-2017, 10:20 AM
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Re: ICC false profiles for color grading/correctio

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Originally Posted by Tony W View Post
Still not getting this. You assign a profile with a lower or higher gamma than the original to attempt to enhance or bring back detail contained in the original data making the image look good then you convert to required output space.

Why, when you can adjust gamma in PS by at least a couple of methods without assigning wrong profiles then converting to bring back into line?

It seems to me that it should be preferable most of the time to use PS tools direct to adjust gamma on the fly with the advantages of both visual clues and the ability to have seamless control of the steps rather than jumping from say gamma 1.0, 1.8, 2.2 etc.

Unless th point is that you know you have received a file that is incorrectly tagged then it seems the proper time to assign the correct profile.
Exactly. There's no free lunch here. The necessarily tools have existed in Photoshop even before it supported ICC profiles!
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  #38  
Old 02-11-2017, 11:51 AM
klev klev is offline
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Re: ICC false profiles for color grading/correctio

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Originally Posted by SZStudio View Post
Are you sure?
Device link and Abstract are just the color correction tools, like curves or shadow/highlights, you can use the Masks, Blend If of the Layer, change the Blend Modes etc.
But the result depends of the color space of the image, sRGB, EktaSpace, ProPhoto etc.

Think different, color correction profiles are huge time savers, you can get the effect in one second, here is an example:
Technicolor Process 4 - 3 Strip
I mentioned that the ICC profile system has an ugly architecture, yet we're stuck with it. I'm willing to concede that there might be some use for this, yet not in the context described. Marameo seemed to depict a workflow in which someone works on an image stored in RGB while cumulative adjustments are stored up and later applied in LAB.

You would normally make adjustments in LAB if they are difficult to achieve using typical adjustment tools in some RGB space. Either way the software will apply a conversion from whatever profile you're in through the PCS to some viewing profile, typically the one stored by your system's cmm for viewing.

My other point was that RGB based adjustments are only problematic in situations where the correlation between channels would be problematic. This isn't every case, especially in something like photoshop where the available tools are tuned for use in RGB color spaces.


Quote:
Originally Posted by marameo View Post
This might be worth pointing out: "Abstract profiles" are ALWAYS Lab to Lab profiles (independent color values e.g. Lab/XYZ inside) whereas usual ICC profiles (sRGB.icc etc..) are the connection between device dependent color space (RGB, CMYK) and device independent color space (Lab, XYZ). Abstract profile maps the original Lab values to the corrected Lab values.

"Device Link profile" is the connection profile between device dependent color spaces (RGB to RGB) without connecting to the device independent color space (Lab, XYZ).

Photoshop will convert from RGB to Lab and back again to RGB when Abstract profile is use.

So, the goal is to create an abstract profile to change the appearence of the image by tweaking the Lab colors without altering the RGB values.
That makes more sense now.

Device link sounds like a way of sidestepping a few particular issues with CMMs, such as unusual clamping. It's most likely implicitly re-referenced with respect to some other space unless they pre-computed mappings to popular color space profiles, such as Adobe 1998 and sRGB. I'm not sure which it is, but it's not possible to generate such a thing without some assumptions. RGB is contextual. It isn't one particular space. The channels values each tell you how to scale a particular function, but they don't tell you the function. That's why you need some translation to a common basis or a particular translation for each one.

It's like this. You need

sRGB --> PCS and PCS --> sRGB

and

Adobe1998 --> PCS and PCS--> Adobe1998

or

sRGB --> Adobe1998 and Adobe 1998 --> sRGB

In the second case, each individual profile needs to understand how it can be translated with any other profile. In the first case each only needs to know how to match a particular PCS. I imagine devicelink profiles made the first step implicit, then tested on commonly used profiles and CMMs.

If your profile converts to LAB, applies some adjustment, then converts back to RGB, that will alter RGB values. If you plan to use them, it has to alter these numbers at some point. I imagine that the tendency to use LAB is either to avoid issues of correlation within RGB channels or create something that can easily be applied by a variety of users with predictable results, independent of their individual working spaces.

The issue of abstract profiles is a bit different, and as I said this is all quite ugly. In fact the first case sounds like an attempt to import what the film industry did with LUTs in a manner that's compatible with ICC's specifications, which were never designed for this kind of thing.

If you're making local adjustments to individual pixels, then these cannot be stored in any kind of profile. That's because your image may not contain unique mappings from the original values to the output values. Consider 2 pixels.

<128,128,128> --> <128,129,128>
<128,128,128> --> <122,128,127>

You now want your CMM to apply a profile based adjustment, yet they're slightly different colors. Either you take a possibly inconsequential loss of detail or you accept that a profile cannot be used to make this particular adjustment.

The slight loss of detail case occurs with a sparse LUT, where values not explicitly stored in the table are interpolated.
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  #39  
Old 02-11-2017, 12:43 PM
Shoku Shoku is offline
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Re: ICC false profiles for color grading/correctio

Quote:
Originally Posted by Tony W View Post
Still not getting this. You assign a profile with a lower or higher gamma than the original to attempt to enhance or bring back detail contained in the original data making the image look good then you convert to required output space.

Why, when you can adjust gamma in PS by at least a couple of methods without assigning wrong profiles then converting to bring back into line?

It seems to me that it should be preferable most of the time to use PS tools direct to adjust gamma on the fly with the advantages of both visual clues and the ability to have seamless control of the steps rather than jumping from say gamma 1.0, 1.8, 2.2 etc.

Unless the point is that you know you have received a file that is incorrectly tagged then it seems the proper time to assign the correct profile.
You are correct, there are plenty of other tools in PS, and they all have uses and limitations. I use curves over selective color when possible, but I also use selective color when the situation demands. I use LAB to increase color saturation in a more natural way than Hue Saturation, but I also use Hue Saturation. 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. As SZStudio said,

"Think different, color correction profiles are huge time savers, you can get the effect in one second."

It's amazing how close you can get with one click, without needing to take the time to determine how your curves are affecting highlights, mid-tones, and shadows. Curving is intuitive once you are familiar with the process, but a one-click profile assignment is quicker, and it works when the situation calls for it. I have never experienced a profile conversion being a negative step. Selective Color, Levels, and other slider tools can cause more damage to the data, and limit further adjustment, than I have ever experienced with a profile assignment and conversion when done properly. The proof is in the final, visual result, which in the end is all that really matters.
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  #40  
Old 02-11-2017, 01:33 PM
Shoku Shoku is offline
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Re: ICC false profiles for color grading/correctio

Quote:
Originally Posted by Tony W View Post

It seems to me that it should be preferable most of the time to use PS tools direct to adjust gamma . . .
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.
Attached Images
File Type: png origial.PNG (185.5 KB, 7 views)
File Type: png Assign.PNG (188.0 KB, 7 views)
File Type: png converion.PNG (211.5 KB, 7 views)
File Type: png curves.PNG (187.8 KB, 8 views)
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