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Author Topic: Correcting images in LAB vs RGB  (Read 19869 times)
joofa
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« Reply #20 on: February 22, 2010, 11:53:24 AM »
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Quote from: digitaldog
As many who knew him would agree, Bruce Fraser was one of the best writers on the subject of imaging and this post, dating back well over a decade is a good read on the subject of using Lab:

It would appear to me that while some of the criticism on the Lab space is justified, such as regarding the origins and intended use of Lab space, but in the quoted note by Bruce Fraser, Bruce has heaped upon Lab some issues that have been incorporated in more modern color appearance models (CAMs) and using that in conjunction with Lab space. The distance formulae in Lab space are also becoming increasingly complex (CIE 94, DE 2000, etc.) and are intended to remove some of the shortcomings mentioned in the note above.


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Michael H. Cothran
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« Reply #21 on: February 22, 2010, 12:07:47 PM »
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Quote from: John R Smith
If you are not working on pixels in RAW, what are you working on? Surely the sensor in the camera must ouput a file which is composed of pixels (one for each sensel) each one representing a location and a colour/lightness value? Or if not, what are they?
John

John - To use an analogy, and I hope I'm correct in saying it this way -

There ARE no pixels in a RAW file. Only data. A "blue print," if you will, on how the file should be constructed. Since, in RAW format, nothing has yet been built, it is more advantageous to adjust the blue print (which is what you would be doing in a RAW converter), than to alter or modify the house once built (which is what you would be doing once pixelized in PS).

Michael
« Last Edit: February 22, 2010, 12:14:20 PM by MichaelHCothran » Logged
digitaldog
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« Reply #22 on: February 22, 2010, 12:15:32 PM »
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Quote from: joofa
It would appear to me that while some of the criticism on the Lab space is justified, such as regarding the origins and intended use of Lab space, but in the quoted note by Bruce Fraser, Bruce has heaped upon Lab some issues that have been incorporated in more modern color appearance models (CAMs) and using that in conjunction with Lab space. The distance formulae in Lab space are also becoming increasingly complex (CIE 94, DE 2000, etc.) and are intended to remove some of the shortcomings mentioned in the note above.

Agreed but just what applications are you referring to that have incorporated such modern CAMs in the context of this discussion of Lab in Photoshop?
I think Bruce is suggesting modern CAMs address the issues he points out and yet, do we have access to them, nearly a decade after this post?
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Andrew Rodney
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joofa
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« Reply #23 on: February 22, 2010, 12:20:08 PM »
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Quote from: digitaldog
Agreed but just what applications are you referring to that have incorporated such modern CAMs in the context of this discussion of Lab in Photoshop?
I think Bruce is suggesting modern CAMs address the issues he points out and yet, do we have access to them, nearly a decade after this post?

I think you are right that Photoshop may not have incorporated more modern models. However, my reply was a general one and not intended towards Photoshop as the quoted text from Bruce Fraser was also more general and perhaps not intended towards Photohsop.
« Last Edit: February 22, 2010, 12:20:34 PM by joofa » Logged

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« Reply #24 on: February 22, 2010, 12:25:22 PM »
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Quote from: joofa
I think you are right that Photoshop may not have incorporated more modern models.

As far as I know, it doesn’t. And editing in Lab in Photoshop has all the issues and more Bruce points out above.
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Andrew Rodney
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« Reply #25 on: February 22, 2010, 01:22:28 PM »
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Quote from: Ishmael.
--open image and convert to LAB color, where I fix up the color cast, contrast, and saturation using multiple curves adjustments layers. Add clarity and noise reduction by converting the background layer to a smart object and applying high pass, luminance NR, and median (for color noise) filters.


All of the above (except for the convert to Lab) would best be done in Camera Raw on a raw file. The advantages would be to offer a far more efficient workflow and optimal final output results.

I won't get into the sRGB vs other color space (nor 8 vs 16 bit) but there is very, very little one can't do in Camera Raw 5.x that has to be done in Photoshop unless you do substantial retouching and/or image assembly. Heck, you can even process out TIFF, PSD or JPEG files from Camera Raw without ever having to open Photoshop (open Camera Raw hosted in Bridge).

Considering Camera Raw was originally written by the same guy who was the primary author of Photoshop (Thomas Knoll) you might think he may have made some advances in image processing this time around...he did.
« Last Edit: February 22, 2010, 02:16:36 PM by Schewe » Logged
Ishmael.
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« Reply #26 on: February 22, 2010, 01:48:20 PM »
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Quote from: Schewe
All of the above would best be done in Camera Raw on a raw file. The advantages would be to offer a far more efficient workflow and optimal final output results.

I won't get into the sRGB vs other color space (nor 8 vs 16 bit) but there is very, very little one can't do in Camera Raw 5.x that has to be done in Photoshop unless you do substantial retouching and/or image assembly. Heck, you can even process out TIFF, PSD or JPEG files from Camera Raw without ever having to open Photoshop (open Camera Raw hosted in Bridge).

Considering Camera Raw was originally written by the same guy who was the primary author of Photoshop (Thomas Knoll) you might think he may have made some advances in image processing this time around...he did.


Thanks Schewe. Does the same go for earlier versions of Camera Raw? I'm using 4.0 on CS3.
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Schewe
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« Reply #27 on: February 22, 2010, 02:19:12 PM »
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Quote from: Ishmael.
Thanks Schewe. Does the same go for earlier versions of Camera Raw? I'm using 4.0 on CS3.

Camera Raw 4.6 (the last version for CS3) doesn't have the benefit of local corrections using gradients of brushes that Camera Raw 5.x does in Photoshop CS4. But for global image adjustments, yes, ACR 4.6 would be good for making important image adjustments.
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HickersonJasonC
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« Reply #28 on: February 22, 2010, 07:31:31 PM »
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Quote from: KeithR
I would suggest that you invest in Mr. Schewe's book "Real World Adobe Camera Raw"

Hilarious advice considering Jeff's typical attack on OP's "reading comprehension." Ironic? LOL in any case!
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Ishmael.
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« Reply #29 on: February 22, 2010, 07:51:50 PM »
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I don't mean to beat this horse to death but I am still not clear on one issue: is it wise to edit in Camera Raw using Pro Photo/16bit  and then convert to sRGB/8bit when I'm saving JPEGs for the web? Or is the conversion back to sRGB just going to undo whatever advantages Pro Photo gave me?
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curvemeister
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« Reply #30 on: February 22, 2010, 08:00:26 PM »
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Quote from: Ishmael.
I don't mean to beat this horse to death but I am still not clear on one issue: is it wise to edit in Camera Raw using Pro Photo/16bit  and then convert to sRGB/8bit when I'm saving JPEGs for the web? Or is the conversion back to sRGB just going to undo whatever advantages Pro Photo gave me?

Camera Raw uses a slightly modified version of ProPhoto internally in any case.  Converting to sRGB can be done at any stage, with no difference in quality.  From a procedural point of view, it saves a step to convert to sRGB coming out of ACR.
« Last Edit: February 22, 2010, 08:04:44 PM by curvemeister » Logged

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« Reply #31 on: February 22, 2010, 08:18:44 PM »
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Quote from: Ishmael.
I don't mean to beat this horse to death but I am still not clear on one issue: is it wise to edit in Camera Raw using Pro Photo/16bit  and then convert to sRGB/8bit when I'm saving JPEGs for the web? Or is the conversion back to sRGB just going to undo whatever advantages Pro Photo gave me?

Not at all a problem.
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Andrew Rodney
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Ishmael.
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« Reply #32 on: February 22, 2010, 09:39:52 PM »
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All your guys help is much appreciated. It's a huge help to me as I'm learning the different aspects of post-processing.  

 
Thanks

Ish.
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Dale Allyn
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« Reply #33 on: February 22, 2010, 09:49:36 PM »
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Quote from: Ishmael.
I don't mean to beat this horse to death but I am still not clear on one issue: is it wise to edit in Camera Raw using Pro Photo/16bit  and then convert to sRGB/8bit when I'm saving JPEGs for the web? Or is the conversion back to sRGB just going to undo whatever advantages Pro Photo gave me?

Ishmael,

If you expect to do more than minor adjustments in PS (after moving from ACR), and if you expect to use that file for more than one type of output (such as for web and for printing to a quality printer with a wider gamut), you may prefer to convert to sRGB after doing your work on the file in PS. In other words, you may consider doing whatever needed in ACR, if moving to PS do so and work in layers there, then save your final masterpiece as a "master version". From this point you can convert to sRGB for web, and if your monitor is one which allows you to see a difference (i.e. a wide gamut display) you could then make whatever tweaks improve your sRGB file needs, convert to 8-bit, sharpen as appropriate and save for web as your needs require.

This way, you can go back to your "master version" in ProRGB and adjust it for printing to your favorite paper, etc. without needing to redo your work.

Also, I would agree that Real World Camera RAW is a good book to have in your library, as well as buying the video here at L.L. "From Camera to Print".
« Last Edit: February 22, 2010, 10:04:53 PM by DFAllyn » Logged

Tim Lookingbill
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« Reply #34 on: February 22, 2010, 11:58:28 PM »
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If you're concerned about ACR 4.6's limitations I can profess after about a year and half working with this version you can still do quite a bit in grabbing every detail your camera can deliver even when you think that images is hopeless and headed for the trash.

Below is a Raw shot from my Pentax K100D, a $477 DSLR. The image on the left is what the jpeg would've given me if I'ld shot it only in that format. As you can see it's a wreck, but the version on the right was all edited in ACR 4.6 on the Raw file in 16 bit ProPhotoRGB using primarily the HSL and curve tool and an extreme adjust to color temp without touching one pixel. All the edits were saved as one XMP rendering instruction file.

If I'ld done it in Photoshop (which I couldn't since the jpeg is shot to hell) I'ld have to go into separate tool dialog boxes and save individual custom named settings making for a very cluttered tool directory to keep track of on the computer for each image.

I'm not saying you'll be able to do this kind extreme corrections at the get go, but it will make you pause the next time you decide throw away an image because it looks like the image on the left. I started in Photoshop back in 1998 teaching myself photo restoration with Photoshop 4 and 5. I applied that understanding playing around with ACR tools to teach myself to get those kind of results.

I suggest you get to know those tools by doing the same. Then the thought of editing in Lab will soon be a distant memory.

Raw editing RULES!
 
[attachment=20432:JpegVsRa...angeFlwr.jpg]
« Last Edit: February 23, 2010, 12:16:57 AM by tlooknbill » Logged
Hening Bettermann
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« Reply #35 on: February 26, 2010, 04:08:47 AM »
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Hi!

The thread has made it very clear that Lab is no good option as an EDITING color space. But I wonder about 2 other potential uses:

1- Since it is a huge space, would it make sense as a space for archiving images?
2- ColorEyes advocates the use of Lab for monitor profiling. What is the experts view on this?

Kind regards - Hening.
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Tim Lookingbill
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« Reply #36 on: February 26, 2010, 12:34:26 PM »
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#1. No

#2. Not sure why ColorEyes would be telling you that. And besides that Lab space has nothing to do with calibration except act as a color reference space to compare one devices color response to a known mathematical definition of color which is all that computers understand. You're comparing Lab as an editing space as apposed to a color reference space. This is why images saved in Lab don't need an embedded profile to work in a color managed workflow because Lab is the reference space for everything and is also the reason you don't get a dialog box prompt of a "Profile mismatch or missing profile" when opening a Lab image in Photoshop. The problem saving images in that space is not all applications can read and/or display it properly.

Too much of a PITA to deal with. Just stick to RGB. This stuff is complicated enough as it is.
« Last Edit: February 26, 2010, 12:38:28 PM by tlooknbill » Logged
digitaldog
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« Reply #37 on: February 26, 2010, 12:38:15 PM »
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Quote from: Hening Bettermann
1- Since it is a huge space, would it make sense as a space for archiving images?
2- ColorEyes advocates the use of Lab for monitor profiling. What is the experts view on this?

As to #1, see what Bruce wrote above:
Quote
For archival work, you will always want to preserve the original capture
data, along with the best definition you can muster of the space of the
device that did the capturing. Saving the data as Lab will inevitably
degrade it with any capture device that is currently available.

Generally speaking, you'll need to do at least one conversion, from input
space to output space. If you use Lab, you need to do at least two
conversions, one from input space to Lab, one from Lab to output space.

As to #2, that, as Tim points out makes no sense. Are you sure you’re not thinking about an L* tone response curve (which is full of controversy too and based on my understanding isn’t anywhere as useful or necessary as some would suggest)?
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Andrew Rodney
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joofa
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« Reply #38 on: February 26, 2010, 01:18:01 PM »
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Quote from: Hening Bettermann
The thread has made it very clear that Lab is no good option as an EDITING color space.

Unfortunately, many authors, and it would appear to me Bruce Fraser included, do not make a clear distinction between what is the theoretical limitation of a space and what is the current implementation of that space/standard/spec/etc. offering. Conflating the two results in notions that people make judgments on theory and algorithmic correctness based upon what a particular implementation (particular software) is doing. For example even in this forum issues regarding the correctness of stuff such as "optimal" sharpening etc., are being done based upon what a particular software, Photoshop, is doing. Of course, I fully realize that a particular software is what people have in their hands so they have to go by that software. However, that is the responsibility of a technical author to clearly delineate which shortcomings in a certain workflow are coming from a particular implementation and which are actual theoretical bounds.

I think I have a few books from Bruce Fraser at home and I shall go and recheck them, but what is quoted of his writings here on this forum, it appears, that Bruce is heaping criticism on Lab space, many of which, in more modern specs, have been assimilated into a theoretical model with Lab (think color appearance models, CAMs, in conjunction with Lab). In theory, it does not matter if Photoshoop does not have them, and an author should point that out that its Photoshop responsibility to modernize and not necessarily the fault of a particular space.

Quote from: Hening Bettermann
1- Since it is a huge space, would it make sense as a space for archiving images?

This is another one of an implementation issue. You would see comments such as that particular space is limited in "gamut", etc. However, in practise, many of those "shortcomings" happen because of certain decision early in the processing chain (such as clipping negative numbers and numbers greater than 1 (normalized) in color values, etc.). The primaries of a color space span the space and if such strippings, etc., are not done early on, and kept in the file all the way to end of the processing chain, when one is about to output, and then gamut mapping/clipping is done, then many of the restrictions of the "small" gamut of a certain space may be resolved.

In essence, notions such as "huge space" are appearing because it is "huge" in positive numbers and less than normalized 1 (though in Lab space, a and b do go negative). Otherwise, negative numbers did not stop CIE to conduct its spectral tristimulus determination experiments in RGB, and then they moved on to all positive XYZ space, because of concerns at that time regarding negative numbers, which should not affect us these days working with computers.
« Last Edit: February 26, 2010, 02:03:46 PM by joofa » Logged

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digitaldog
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« Reply #39 on: February 26, 2010, 01:35:07 PM »
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Quote from: joofa
In theory, it does not matter if Photoshoop does not have them, and an author should point that out that its Photoshop responsibility to modernize and not necessarily the fault of a particular space.
\

Having color appearance models and having color appearance models implemented in imaging software are two very different things.

What products have such color appearance models?
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Andrew Rodney
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