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Newb: out of gamut colors and color shift

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  #11  
Old 01-16-2011, 12:27 PM
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andrewrodney andrewrodney is offline
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Re: Misinformation Warning

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Originally Posted by Markzebra View Post
Thats not true. It's not useless, and certainly not outdated at all. If you are retouching using Adobe RGB, or even more worryingly Pro-photo RGB, then you will certainly need to get some idea of what you are doing using Gamut Warning and Proof colors.
Why? You’ll have to clip the gamut upon conversions. Its as simple as that. The overlay treats a 1% outside gamut and 100% identically! Perhaps if it provided an overlay where one color was 1-10%, another was 11-25% etc, as many other out of gamut utilities can provide, at least you’d know what you are looking at. But at some point, you have to convert to an output space. You should soft proof and see the relationship of the colors based on the rendering intent (and ideally, on a newer wide gamut display).
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  #12  
Old 01-16-2011, 02:15 PM
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Markzebra Markzebra is offline
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Re: Newb: out of gamut colors and color shift

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Why? You’ll have to clip the gamut upon conversions.
Again not true I'm afraid. You only have to "clip" over-saturated colors, if you have produced them by dodgy color retouching in your image. You don't have to lose anything if you know what you are doing. Thats the point, and what Gamut warning and Proofing is for. An RGB where all the colors are roughly within the CMYK gamut, will not be damaged the same way on conversion. Rendering intents only deal with out of gamut colors, and use flawed, compromised methods to bring them into gamut…

Rendering intents: Relative tries for the most saturated version of a color it can produce in CMYK, and as a result sometimes does a bad job of transitions in saturation. Perceptual: will bring everything in to order in a smoother more graduated way. But its more liable to under-saturate colors.

No one is saying these two Rendering Intents are bad, but when working with highly saturated images, its much better to avoid depending on them to salvage your poorly retouched RGB image.

Last edited by Markzebra; 01-16-2011 at 02:26 PM.
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  #13  
Old 01-16-2011, 02:32 PM
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andrewrodney andrewrodney is offline
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Re: Newb: out of gamut colors and color shift

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Originally Posted by Markzebra View Post
You only have to "clip" over-saturated colors, if you have produced them by dodgy color retouching in your image.
Colors are either in or out of gamut of the destination color space. If they are out of gamut, they clip (clip differently depending on the rendering intent but clip none the less). Seeing that your colors clip prior to clipping doesn’t change that a lick.


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You don't have to lose anything if you know what you are doing.
I don’t know what you mean by lose. If you have an output color space, say SWOP V2, or even an Epson 3880/Luster and your original is in say ProPhoto RGB AND there are colors in that working space that fall outside the gamut of either, when you convert, all those colors outside the destination color space clip. You can see this visually with the overlay, that doesn’t change these facts.

You can rub the overlay with the desatruation sponge which is incredibly crude and time consuming considering that as I pointed out, a 1% and 99% out of gamut color are treated the same. Or you can use the ICC profile and the rendering intent to do this in a far more robust and controllable way. The gamut mapping doesn’t treat 1% and 99% the same (with a Perceptual intent even in gamut colors can be affected to preserve color harmony with out of gamut colors). But either way, out of gamut colors get clipped into gamut! The overlay has zero role here. Its simply a visual tool and not a very good one at that.

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Thats the point, and what Gamut warning and Proofing is for. An RGB where all the colors within the image are roughly within the CMYK gamut, will not be damaged the same way on conversion.
Again, the word damage makes no sense here. Define damage. And you are incorrect, all out of gamut colors are affected by the conversion. What the overlay shows has not role in what an ICC profile does during a conversion. Further, please show me a CMYK and RGB color space where some of the gamut doesn’t exceed in one space or the other. You can’t define a saturated cyan in sRGB, you can define colors in sRGB you can’t define in CMYK etc. There’s always some in and out of gamut color mapping somewhere in color space.

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Rendering intents only deal with out of gamut colors, and use flawed, compromised methods to bring them into gamut…
Sounds quite ridiculous but please provide a reference to this “fact”. And since we are using ICC profiles to convert the data anyway, what relevance would this have if true (which is a highly suspect concept).

Quote:
Rendering intents: Relative tries for the most saturated version of a color it can produce in CMYK, and as a result sometimes does a bad job of transitions in saturation. Perceptual: will bring everything in to order in a smoother more graduated way. But its more liable to under-saturate colors.
That’s a very poor understanding of rendering intents. You need to do a bit more study here. And the facts are, there is no specification for conducting a Perceptual Rendering intent. Three different profile making products, measuring the same target data (being fed the same lab values) will produce different results from their Perceptual tables.

Quote:
No one is saying these two Rendering Intents are bad, but when working with highly saturated images, its much better to avoid depending on them to salvage your poorly retouched RGB image.
So would you care to tell us how you are going to convert the data to CMYK or RGB without a rendering intent (at least in Photoshop)? You’ve got this overlay. You have to covert the data. Just what do you propose to do?

Last edited by andrewrodney; 01-16-2011 at 02:37 PM.
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  #14  
Old 01-16-2011, 02:45 PM
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Re: Newb: out of gamut colors and color shift

Each device has a range of colors that it can reproduce, and that range is described within the device’s color space. Colors that are available in one color space but not available in another color space are called out-of-gamut colors. Colors in the original (source) color space need to be mapped to colors that exist within the gamut of the new (destination) color space. There are two basic techniques for mapping out-of-gamut colors. One technique is to take all the colors that are out-of-gamut and map them to the closest colors that are within color gamut of the destination. We call this technique gamut clipping. The second technique is to compress the range of color into the gamut of the destination. It is important to note that when using this method, some colors that were perfectly matched between the two devices will actually change. We call this method gamut compression although one could considering the out of gamut colors clipping into gamut in a disproportion method.

The ICC system provides different methods of gamut mapping and calls these rendering intents. When you perform ICC color transformations within an application, you will need to choose a rendering intent. The rendering intents were created for different situations. The names of the renderings are colorimetric, saturation, and perceptual.

The colorimetric method is a form of gamut clipping. The saturation intent is also a form of gamut clipping, but attempts to preserve the saturation of colors over lightness. The perceptual method is a form of gamut compression. When using the perceptual method, visual detail and luminance are preserved over hue and saturation.

The absolute colorimetric rendering intent reproduces the exact color that existed in the source—absolutely. If the source was light color on the dingy yellow-white of newsprint, the resulting color on your brilliant coated ink jet paper will be dingy yellow. This intent is really designed for making one device simulate the appearance of another device for use in proofing.

•Simulate Paper Colorand Simulate Black InkOff: Convert using the
relative colorimetric intent with Black Point Compensation.
•Simulate Black Ink: Convert using the relative colorimetric intent
without Black Point Compensation.
•Simulate Paper Color: Convert using the absolute colorimetric
intent (no Black Point Compensation).


The perceptual rendering intent transforms the colors so that the image in the destination space is perceived in the same way as the original. The conversions are weighted to deal with luminance over saturation and hue because our eyes will notice differences in luminance far more than differences in saturation or hue. Luminance information provides shape and detail; this is the most important factor to perception.
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  #15  
Old 01-16-2011, 03:53 PM
creativeretouch creativeretouch is offline
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Re: Newb: out of gamut colors and color shift

Andrew, I have found very useful to be aware of colors which are out of gamut. If you work on the photograph, you wish the final result will look in a "similar" way on any device or paper. So I try to keep all colors "inside safe gamut" even if I work in LAB colorspace ...
And now you say this "gamut warning" tool is too old to be taken seriously? Why is still present in Photoshop? Can I trust what I see as a gamut warning? Thank you for your explanation - Filip
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  #16  
Old 01-16-2011, 04:43 PM
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Markzebra Markzebra is offline
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Re: Newb: out of gamut colors and color shift

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Colors are either in or out of gamut of the destination color space. If they are out of gamut, they clip (clip differently depending on the rendering intent but clip none the less).
Thats exactly what I said. I humbly suggest it might be more successful to try and disagree with my point, if the objective is to try and undermine it in some way.

Lets remind ourselves, this started with you making the incorrect statement…

Quote:
The gamut warning is pretty useless! Its legacy functionality from Photoshop prior to version 5
The most intelligent way to work is not to retouch using colors out that are massively out of the destination gamut. Gamut Warning and Proofing functions are provided to help with this. And are not, as you suggested, purely legacy functions.

Repeating this more clearly, because you are seem to be unable to read my points clearly, or are perhaps willfully misreading them: My suggestion is that it is bad practice to work with an RGB image for print, that has many ranges largely out of CMYK gamut. There is no value in doing it this way. It will produce all kinds of problems. For example, you will likely be sending samples to your client with colors that are not produceable on conversion. And judgments on the image while working within these highly saturated colors will be compromised.

I have a very good understanding of what the intents do, and worked specialising in the field of profiling and color for three years. My statement is an accurate summary of what the two usable Photoshop rendering intents do. And what the differences between them are in practice for Retouchers. I made no reference to any other software as you did, and am unable to see the point in bringing that up.

Quote:
You can rub the overlay with the desatruation sponge which is incredibly crude and time consuming
To be honest I'm not sure what that can say about your Photoshop skills, if you think it would still be done that way.

My statement…

Quote:
Rendering intents only deal with out of gamut colors, and use flawed, compromised methods to bring them into gamut
Pulling high gamut RGB spaces into CMYK will always be a compromise. To avoid this compromise, its best as far as possible not to make it. Since there is no loss whatsoever in taking a conservative approach to saturated color in RGB, its the best approach. If you are under the impression, as you seem to be, that all CMYK conversions do the same damage regardless of image content, then unfortunately I suggest you do your homework.

Quote:
So would you care to tell us how you are going to convert the data to CMYK or RGB without a rendering intent (at least in Photoshop)? You’ve got this overlay. You have to covert the data. Just what do you propose to do?
Again you completely misunderstood what I wrote, and I suggest you read it again. To clarify , you are suggesting depending on the Intent to deal with your out of gamut colors. I'm saying that the smartest approach is to avoid the Intent having to pull the colors too far. Its easier to work with.

Last edited by Markzebra; 01-16-2011 at 04:52 PM.
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  #17  
Old 01-16-2011, 05:58 PM
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Re: Newb: out of gamut colors and color shift

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Why is still present in Photoshop? Can I trust what I see as a gamut warning?
Its present in Photoshop for the same reason the legacy CMYK color engine is still in Photoshop (Adobe rarely if ever removes anything). Can you trust what you see with the gamut warnings? Not really because again, the overlay treats everything equally. Its far more effective to soft proof and SEE what the colors will look like based on the rendering intent.
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  #18  
Old 01-16-2011, 06:07 PM
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Re: Newb: out of gamut colors and color shift

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My suggestion is that it is bad practice to work with an RGB image for print, that has many ranges largely out of CMYK gamut.
Today, most users have to work with multiple output needs. Its really silly to funnel RGB into a small color space for one use (CMYK). And as I said, there’s all kinds of colors within even the smallest RGB working space (sRGB) that is out of nearly any CMYK output color space. So you can’t work solely as you propose. The gamut shapes of sRGB (any RGB working space) and any CMYK and most all RGB output spaces are severally different. Easy to illustrate with 3D gamut maps that I can point you to.

Moving out of gamut colors into gamut is something we’ve done for decades. It has to be done. You have the option of using a tiny RGB working space like sRGB and penalizing all other output color spaces than CMYK or you can work with a larger gamut working space and simply map out of gamut colors to CMYK and lots of other output color spaces, again using ICC profiles and a rendering intent you select. NONE of this has any bearing on the gamut warning overlay! Or to put it another way, the gamut overlay has no role in the gamut mapping, it simply shows you all out of gamut colors. And not in a very intelligent way! What you now do is key. You have to convert using ICC profiles, unless you are converting colors using some copy of Photoshop earlier than Photoshop 5 circa 1998. Those are simple facts.

Quote:
I have a very good understanding of what the intents do, and worked specialising in the field of profiling and color for three years.
Then what you wrote above must have come elsewhere because its quite inaccurate and a bit sloppy.

Quote:
Pulling high gamut RGB spaces into CMYK will always be a compromise.
No more than pulling smaller RGB spaces that are out of CMYK gamut is a compromise. You can’t fit round holes in square pegs here. FWIW, users have been using very wide gamut spaces for CMYK output for a decade or more. Devices who’s “gamut” is hugely larger than film and any CMYK output space.

Quote:
If you are under the impression, as you seem to be, that all CMYK conversions do the same damage regardless of image content, then unfortunately I suggest you do your homework.
You keep using the term “damage” without defining what you mean. That along with the post about rendering intent makes me suspicious of your understanding of this topic but lets wait a bit and why don’t you explain what you mean.

Quote:
To clarify , you are suggesting depending on the Intent to deal with your out of gamut colors. I'm saying that the smartest approach is to avoid the Intent having to pull the colors too far.
Provide a demonstrative way to prove that point will you?
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  #19  
Old 01-16-2011, 06:28 PM
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Re: Newb: out of gamut colors and color shift

Quote:
Originally Posted by Markzebra View Post
Rendering intents: Relative tries for the most saturated version of a color it can produce in CMYK, and as a result sometimes does a bad job of transitions in saturation. Perceptual: will bring everything in to order in a smoother more graduated way. But its more liable to under-saturate colors.
Some reading material:

http://www.ppmag.com/reviews/200405_rodneycm.pdf

http://www.adobe.com/digitalimag/pdf...p_colspace.pdf
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Old 01-16-2011, 10:15 PM
5nap5hot 5nap5hot is offline
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Re: Misinformation Warning

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Originally Posted by Markzebra View Post
...or even more worryingly Pro-photo RGB..
Ok I need an education.

I will state for the record that I am a photographer first. I was always told that I "should" be using ProPhoto RGB to process my images. Because of this, I use ProPhoto RGB as my default colorspace in photoshop.

Could someone explain why ProPhoto is bad? Why would people recommend it?
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