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Color and luminance separation comparison results

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  #11  
Old 06-19-2011, 12:04 AM
Flashtones Flashtones is offline
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Re: Color and luminance separation comparison resu

Thanks John.

Sure, setting adj layers to Lum, hue, sat or color is the usual approach. I'm wondering in what situations one would go the next step to actually separating the image into luminosity and chromacity layers before adding adjustment layers?

IOW, why physically separate the color from the luminosity (using the plugin or your alternative approach) when we can effectively do the same with adj layers and blend modes?
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  #12  
Old 06-19-2011, 07:14 AM
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Der_W Der_W is offline
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Re: Color and luminance separation comparison resu

Because we can't (at least not fully).

The problem with the blending modes is that they take effect after the adjustments were applied.
I did a test image here where I first drew an overlay curve and then applied it in "Color" mode.

This is the original: http://dl.dropbox.com/u/7124285/JW-P...pieren_PRE.jpg
This is the curves applied in "Color" mode: http://dl.dropbox.com/u/7124285/JW-P...erkopieren.jpg
This is the curves applied to the color directly: http://dl.dropbox.com/u/7124285/JW-P...eren_Farbe.jpg

As you can see when the curve is applied to the color, the results are richer and less shadows/highlights desaturate.


On the other hand personally I haven't found much use for this separation in my workflow as I tend to work out the main color and luminosity in the RAW converter, so no need for this kind of curves.

Jacob Rus at the Applied Color Theory newsgroup also wrote a reply to a somewhat similar question. Here's the advantages and disadvantages of the separation he came up with:

Quote:
Originally Posted by Jacob Rus
To my mind, here are advantages:

* Not all filters work in CIELAB mode
* The curves dialog is designed for RGB and is a horribly inflexible and
limited interface in CIELAB mode; this can be improved somewhat by
doing something like the "ladder" trick, but even that is far from ideal.
* You can't use the exclusion blending mode in CIELAB mode. This is
really tragic because the combination of exclusion + linear light mode
layers allows some really powerful tricks.
* Some RGB color space might be your intended output space, in which
case you won't have to worry about gamut clipping between working
view and final output.

And the disadvantages:

* Photoshop's way of splitting "luminosity" (a term made up by Adobe)
from "color" is an extremely bad approximation of the way the chromatic/
achromatic components are split by human color vision. The mathematical
computation it does is only actually meaningful when gamma = 1.0, and
the primaries in use are the NTSC primaries. When you use sRGB, the
computation is essentially arbitrary. In practice any kind of operation
performed by Photoshop luminosity/color severely distorts every color
relationship in a usually undesirable way. CIELAB is a much better
approximation (though it suffers some big problems with hue constancy
along radial lines).
* RGB is an extremely unnatural way to break up the colors of an image,
so every time you do anything with tools like hue/saturation, curves,
etc. you'll end up severely distorting hue, chroma relationships between
colors, or else spending inordinate amounts of effort trying to avoid
such distortions. This is true whether you work on your original image
or work with some intermediate processed form.
* If you plan to output CMYK, it's very difficult to get the content of your
image to properly fill the CMYK gamut in most RGB working spaces.

There are probably some other advantages/disadvantages, but this is
enough of a list for now. :-)
See the full post here if you're a member of the group: http://tech.groups.yahoo.com/group/c.../message/23975
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  #13  
Old 06-19-2011, 08:19 AM
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John Wheeler John Wheeler is offline
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Re: Color and luminance separation comparison resu

Hi Flashstone

For most basic image processing as Jonas also mentioned, I too use Lightroom (or ACR) and sometimes don't even need to go to PS.

There are two approaches that I think about where I use this type of capability

1) Specific turn the crank how to I solve a specific problem type of approch. Here are just two examples of how I have used the separation
- For mask creation, for me it is how do I best separate out what I want from what I don't want. Separating out the Luminosity/Hue/Sat provides me options for mask creation that is a new angle compared with other approaches.
- For eliminating some camera sensor based Moire patterns per my previous post on ReTouchPRO and here is the direct link to my blog (details in the screencast): http://jkwphoto.blogspot.com/2011/05...ove-moire.html
- many many other approaches yet point 2 may better explain why

2) Second way of looking at how to use the separation: On a broader base of thinking about the value of separating out Luminosity and Color (Hue and Sat) is basically identical to why you would want to see the individual channels of any color model/mode. Why would you want to see or manipulate the individual channels of RGB. Why would you want to see or manipulate the individual channels of LAB. Why would you want to see or manipulate the individual channels of CMYK. Basically it gives me insight to the image and the problems I am trying to solve. It also provides approaches to the solution that are not available when the channels are just all combined with each other.

The main difference with the Luminosity/Hue/Sat model embedded in the RGB model is that you don't have a channels panel to have immediate easy access to each separate channel so you have to pull them out with a Layers approach.

I am certainly not trying to sell this technique for anything special. Just another technique within PS among many others. So I will leave this with you to think about. Every time you hear about a technique that touts the major advantages of converting to LAB mode so the the color and Luminosity are separated and can be manipulated separately, there is often a way to do the same thing (or very similar) from right within RGB using the separation techniques talked about above. Each color mode/model has its strengths and weaknesses so this is just another option to explore.

So what is it good for? Sometimes you have to go exploring to find out just like exploring any other available color model/mode. Hope that helps.
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  #14  
Old 06-19-2011, 11:52 AM
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andrewrodney andrewrodney is offline
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Re: Color and luminance separation comparison resu

I too have to wonder what the practical implications of all this really is. We have a process designed by Thomas Knoll way back in 1990, whereby there is a boost in saturation (which I suppose produces what some are saying is a hue shift?) when altering “luminosity” (the wrong term but one we have to live with). We also have the ability to use blend modes to counter this designed effect. According to Thomas, there’s a lot more code involved doing the move as he designed it, and he designed it because *most* users prefer the rendering. But its not forced upon us.

It seems that for many years, the idea that having this rendering was wrong. Colorimetrically? I suppose. What about the results of this distortion or lack of distortion when once again, we have to convert the data to an output color space? What appears preferable to the user, with or without the ‘shift’ is all that matters. And it appears this is a bit moot if you do all this work in a raw converter which I think makes far more sense for so many reasons.

I think the question should be, with the two (or even more) options in Photoshop alone, is there a need for a 3rd party product? If one decides to do all the heavy lifting in terms of global color and tone work from raw, is there any difficulty with the current Adobe tools and if so, are there other raw converters that solve this problem if the problem even exists?


Quote:
In practice any kind of operation
performed by Photoshop luminosity/color severely distorts every color
relationship in a usually undesirable way.

RGB is an extremely unnatural way to break up the colors of an image,
so every time you do anything with tools like hue/saturation, curves,
etc. you'll end up severely distorting hue, chroma relationships between
colors, or else spending inordinate amounts of effort trying to avoid
such distortions.
This may be true in the context of the math. But the image(s) itself? Can someone illustrate the distortions such that using either of the above Photoshop methods, or an Adobe raw converter, the image is unacceptable visually? I don’t care about the math behind the process, I care about the image rendering.
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  #15  
Old 06-19-2011, 11:56 AM
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andrewrodney andrewrodney is offline
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Re: Color and luminance separation comparison resu

Oh, and in terms of having this distortion or lack of distortion while working in RGB or otherwise, there’s no such distortion in either case when converting to an output color space or even another RGB working space? Considering the effect of rendering intents on a conversion, I kind of doubt it. Is this all a solution in search of a problem?
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  #16  
Old 06-19-2011, 03:05 PM
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John Wheeler John Wheeler is offline
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Re: Color and luminance separation comparison resu

Quote:
Originally Posted by John Wheeler View Post
The efficacy of accurately reproducing the Lobster extracted colors I believe is in question. The reason being is that it (as well as PS) is based on a definition of Saturation which IMO was based on computational efficiency rather than meaningfulness from a color model.
I would have to agree with Andrew (glad to cross paths with you again). For a $99 plugin the value add does not seem to be there IMHO. I also did not mind doing the little bit of evaluation though because it did sound initially intriguing. Sometimes there really is a difference in what tools have to offer. With the initial look though, I have not been intrigued enough to download the evaluation copy. If there is someone out there with more knowledge of the tool and why it would be worth purchasing, it would be great to hear.
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  #17  
Old 06-20-2011, 08:50 AM
e2b e2b is offline
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Re: Color and luminance separation comparison resu

Quote:
Originally Posted by John Wheeler View Post
If there is someone out there with more knowledge of the tool and why it would be worth purchasing, it would be great to hear.
As I understand it, Lobster makes two claims:
1. That separation of luminosity from chromaticity is useful.
2. That of the various possible sets of chromaticities that could be separated from luminosity, the set that Lobster produces is particularly (if not uniquely) useful.

I too would be interested in hearing about how these claims stand in the light of practical experience.

I have managed well enough until now without finding a need for this sort of separation, but nevertheless I have found this whole thread absolutely fascinating, especially the insights into the inner workings of PS - thanks Der_W, for drawing it to my attention

Steve
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  #18  
Old 06-20-2011, 10:14 AM
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John Wheeler John Wheeler is offline
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Re: Color and luminance separation comparison resu

Quote:
Originally Posted by e2b View Post
...nevertheless I have found this whole thread absolutely fascinating, especially the insights into the inner workings of PS - thanks Der_W, for drawing it to my attention
Steve
Hi Steve and any other ReTouchers that are also fascinated by the inner workings of PS (isn't that the definition of a fellow gearhead? ) then here is a reference for you (WARNING - not directly useful to the retoucher unless you need the math insights)

Buried away in Adobe's "PDF Reference and Adobe Extensions to the PDF Specification" is a boatload of details on their inner workings of Adobe software including Photoshop. This document is "in theory" a common reference for all their Adobe products (not sure I really believe that). In any case, the math for all the blending modes (including Color, Hue, Sat, Luminosity and all the others) are found starting around 320 of this PDF document with the actual blend equations starting on page 324 (told you it was buried).

Here is the reference to the PDF file for the original PDF document:

http://wwwimages.adobe.com/www.adobe...32000_2008.pdf


Here is the reference to the Adobe page with all the udpates to that document.

http://www.adobe.com/devnet/pdf/pdf_reference.html

And yes, the word "fascinating" is in the eye of the beholder
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  #19  
Old 06-20-2011, 07:30 PM
Flashtones Flashtones is offline
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Re: Color and luminance separation comparison resu

Thanks for the thorough replies. I've played with the separation at various times in the past thanks to the actions of a certain generous poster here (shout out to Jonas!)

It's interesting and fun, but I just always forget to break it out for use when I'm actually working and not just testing.

Jonas, I agree in your provided example it looks better. Interestingly, it more resembles a HSL layer set to about +45 saturation than it does a curve in color mode. However, it seems to do so with less banding in the background, thought I wonder if that might be because the original you worked on was higher bit or less jpegged than the original I borrowed (solely for this test of course) from your post?
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  #20  
Old 06-21-2011, 06:55 AM
e2b e2b is offline
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Smile Re: Color and luminance separation comparison resu

Thanks for the links to reference material John. It is not just the mathematics that interested me, but the insights into quirky things like the special definition of luminosity, inconsistencies in usage between different modules within PS, etc. (thanks Jonas). I guess there must have been many decisions made in the process of developing PS, which were expedient at the time, but now seem hard to explain.

To me, PS is essentially a very successful commercial product that satisfies the vast majority of its users, even if it does some odd things internally - it is not intended to be a sort of universal programming language. However, it has become such a standard tool that people seem compelled to go out of their way to achieve within PS (with actions, plugins and droplets) that are not really in its nature.

Sometimes it is better to do things outside the constraints of PS, with Lightroom being a case in point.

Steve
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