Luminous Landscape Forum
Raw & Post Processing, Printing => Digital Image Processing => Topic started by: Jason Cory on February 07, 2006, 01:36:17 pm
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I've been searching the forums and while I've read a lot about Out-of-Gamut colors, I can't seem to find a simple answer to this question:
How do I get my Out-of-Gamut colors back In-Gamut?
Perhaps there is no simple answer to this question. I hope that's not the case, but I'd appreciate any info on the subject. Links or suggested reading also appreciated.
I have Adobe Photoshop CS2 for Photographers coming from Amazon. Hopefully that will clear some things up. Thanks.
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Sorry, I guess I should give a little more info about my workflow. I'm running PS CS2, using Bridge and ACR exclusively and my color profile is set to ProPhoto RGB. I output my raw files from .DNG to TIFF with Layers after processing. At present, I don't have a printer, so printer profiling isn't an issue for now. If it matters, I'll probably buy an Epson R2400 soon or order prints from a Pro Lab with a Fuji Frontier.
Thanks again,
Jason
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You will only get out-of-gamut colors when you convert to another working space or color profile. IOW, if you stay in ProPhoto (your working space), you'll only get out-of-gamut colors when you print -you convert to your printer profile- or convert to sRGB to post your photos on a website. The process of dealing with out-of-gamut colors is controlled by the rendering intent. Since you use Photoshop you can soft-proof and see how the different rendering intents affect your photos. The most commonly used intents are perceptual and relative colorimetric.
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Rendering Intent - Perceptual (causes the full gamut image to be compressed into the gamut of the destination) or Relative Colorimetric (converts out of gamut colors to colors that are inside the gamut - clips the out of gamut colors)
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Rendering Intent - Perceptual (causes the full gamut image to be compressed into the gamut of the destination) or Relative Colorimetric (converts out of gamut colors to colors that are inside the gamut - clips the out of gamut colors)
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OK, I have my color conversion setting set to PERCEPTUAL in the color settings box. Is this what you are talking about?
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Colors are only out of gamut when you try and reproduce them on a device that can't make those colors. When you do try and print them, and you have colors that ARE out of your printer gamut, you have two choices. Either the out of gamut color gets clipped and becomes the closest in gamut color, which is what happens when you use Relative Colorimetric rendering intent, or , all the colors get shifted slightly and the out of gamut color still becomes the closest in gamut color, which is what happens when you choose Perceptual rendering intent.
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Jason,
You may find useful information about rendering intents here (http://www.cambridgeincolour.com/tutorials/color-space-conversion.htm).
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I'll throw another wrench into this. Unless you've just dropped $5-$6K on a wide gamut display, you're not seeing anything on screen outside sRGB gamut.
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I am a wee bit confused...............
I am using Capture One, PS CS on a PC laptop.
CaptureOne is set to 16bit, ProPhoto RGB. Its colour management settings are set to my Canon 20D and SRGB.
CS is set to ProPhoto RGB, CMYK Euroscale Coated v2.
I take great care exposing to the right and the adjusting in CaptureOne before converting.
On my laptop's monitor I almost always get some colours out of gamut.
Even when I don't get them, they will usually appear during sharpening or increasing saturation.
Is it possible that technically there is nothing wrong with what I am doing and that it is the limitations of the monitor that is causing this?
I mainly shoot artwork for reproduction and, while the amoun of 'out of gamut' on a given painting or drawing is usually tiny, I'd still like to know where it's coming from.
Thanks.
D.
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Andrew, your "wrench" isn't much of a monkey, because when you work in ProPhoto and softproof to an Epson printer profile, you can still see a helluva difference (at least on my Sony CRT monitor you can), and that helps the monitor-to-print matching 95% of the way if you're well profiled and calibrated. But then again, you didn't say it was a monkey-wrench.
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Andrew, your "wrench" isn't much of a monkey, because when you work in ProPhoto and softproof to an Epson printer profile, you can still see a helluva difference (at least on my Sony CRT monitor you can), and that helps the monitor-to-print matching 95% of the way if you're well profiled and calibrated. But then again, you didn't say it was a monkey-wrench.
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True. Even using a sRGB display, you still benefit from a soft proof. Only the very wide gamut color outside any display remains "invisible". With Ink Black/Paper White, you benefit from a much better soft proof of the prints dynamic range even with an sRGB gamut display.
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Rendering Intent - Perceptual (causes the full gamut image to be compressed into the gamut of the destination) or Relative Colorimetric (converts out of gamut colors to colors that are inside the gamut - clips the out of gamut colors)
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Tim,
I assume you are THE author Tim Gray. Let us say that you are using Adobe Camera Raw and note that a certain raw image shows color slight clipping in sRGB and you use ProPhotoRGB to encompass the whole image. Of course the gamut of ProPhotoRGB is considerably wider than the gamut of the image. Now, if you print to a device with a gamut similar to sRGB and use the proper table profile to convert from ProPhotoRGB to the device, how is the conversion done?
Does it compress the entire ProPhotoRGB gamut to the device profile, or use just enough compression to cause the colors actually used in the picture to fit into the gamut of the output device? In the first case, considerably more compression than necessary would be used and the colors might appear flat.
Bill Janes
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ALL conversions from simple matrix profiles (which is how all RGB working space profiles are built) can only be conducted with the Colorimetric table. There is no Perceptual table in those profiles.
Yes, in Photoshop you can select sRGB and pick Perceptual to convert from ProPhoto. You're going to get a Relative Colorimetric intent unless you specifically select Absolute (which would look butt ugly). The Colorimetric table is used for both RelCol or Absolute.
When converting from ProPhoto RGB to sRGB, you're never getting Perceptual.
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I assume you are THE author Tim Gray. Let us say that you are using Adobe Camera Raw and note that a certain raw image shows color slight clipping in sRGB and you use ProPhotoRGB to encompass the whole image. Of course the gamut of ProPhotoRGB is considerably wider than the gamut of the image. Now, if you print to a device with a gamut similar to sRGB and use the proper TABLE [BASED] profile to convert from ProPhotoRGB to the device, how is the [perceptual] conversion done?
Does it compress the entire ProPhotoRGB gamut to the device profile, or use just enough compression to cause the colors actually used in the picture to fit into the gamut of the output device? In the first case, considerably more compression than necessary would be used and the colors might appear flat.
Bill Janes
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ALL conversions from simple matrix profiles (which is how all RGB working space profiles are built) can only be conducted with the Colorimetric table. There is no Perceptual table in those profiles.
Yes, in Photoshop you can select sRGB and pick Perceptual to convert from ProPhoto. You're going to get a Relative Colorimetric intent unless you specifically select Absolute (which would look butt ugly). The Colorimetric table is used for both RelCol or Absolute.
When converting from ProPhoto RGB to sRGB, you're never getting Perceptual.
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Digidog,
Thanks for the reply, but you did not answer my question. I was assuming a TABLE based profile (such as Drycreek.com) with a gamut similar to sRGB, not a matrix based sRGB table. In this case, how would the perceptual converson be performed?
Bill Janes
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I seriously doubt you'll find a lUT based profile of an output device that looks anything like sRGB. When you look at working space gamuts, you see they have a very simple shape due to how the primaries are defined mathematically. One of the reasons we need large(er) gamut spaces is due to this shape mismatch. Take ProPhoto RGB. The blue primary was designed to be saturated (to the point it falls outside the CIE chromaticity plot). You need a big honkin triangle in shape so that much smaller but odd sized output color spaces can be contained. It's a bit like trying to fix a square peg in a round hold. The round hole has to be much larger in size to fit this odd shape and indeed, a lot of the curves in the shape are not used but are necessary to make the fit.
As mentioned, when you do gamut mapping and have all the intents available you can clip colors to the boundaries of move all colors in a way to attempt to perceptually keep all colors appearing "the same" or keeping the color relationships as they were prior to the mapping.
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.
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.
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Digidog,
I know that you have written the Fuji Frontier and other commercial photo printers do not have sRGB as their color space, but merely convert the sRGB data to their own gamuts. The assumption of an output device with sRGB characteristics was merely hypothetical.
Unfortunately, you still have not answered my original question. If you are using ProphotoRGB with a moderately sized gamut image and printing to a relatively smaller gamut device using perceptual rendering with a table based profile, does the gamut compression occur for the entire ProphotoRGB gamut or only to the extent of bringing the out of gamut colors into gamut?
The latter instance would require a "smart algorithm" that actually looks at the contents of the file to determine the extent of compression required, whearas the former would simply squash down the whole ProphotoRGB gamut.
Bill Janes
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Digidog,
I know that you have written the Fuji Frontier and other commercial photo printers do not have sRGB as their color space, but merely convert the sRGB data to their own gamuts. The assumption of an output device with sRGB characteristics was merely hypothetical.
Unfortunately, you still have not answered my original question. If you are using ProphotoRGB with a moderately sized gamut image and printing to a relatively smaller gamut device using perceptual rendering with a table based profile, does the gamut compression occur for the entire ProphotoRGB gamut or only to the extent of bringing the out of gamut colors into gamut?
The latter instance would require a "smart algorithm" that actually looks at the contents of the file to determine the extent of compression required, whearas the former would simply squash down the whole ProphotoRGB gamut.
Bill Janes
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First, the Frontier only assumes sRGB as the source color space when converting to the destination color space. In any conversion, you have to define the source and the destination. Both are equally important.
A working space is a container for holding you image data and it has a fixed gamut. You can shoot a gray card in RAW and encode that data into two working spaces of differing gamuts. It might fully fit within sRGB and it will of course fit in ProPhoto with a heck of a lot of additional gamut around this data. So looking at the scene gamut before even deciding what working space to use for encoding is useful. If you can fit this gray into sRGB, using ProPhoto buys you nothing.
OK you have a very saturated scene gamut that required ProPhoto RGB and you need to convert it into sRGB to place on the web. In this case your "suck" with RelCol gamut compression due to the profile structure.
You have an image and you want instead to map it to a printer color space and it's smaller. The compression will take place at the boundaries of the image gamut as you should see in the screen dump I placed in my last post. Hopefully you can see that there are colors that are not at the boundaries of the larger triangle. Some may be, some may not be but the area where a color lies in the chromaticity diagram is where the mapping starts. Does that answer the question?
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You have an image and you want instead to map it to a printer color space and it's smaller. The compression will take place at the boundaries of the image gamut as you should see in the screen dump I placed in my last post. Hopefully you can see that there are colors that are not at the boundaries of the larger triangle. Some may be, some may not be but the area where a color lies in the chromaticity diagram is where the mapping starts. Does that answer the question?
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More or less. Your screen dump contains colors at the boundaries of the larger space; therefore, the whole larger gamut would have to be compressed down, starting with the boundary; the colors closer to the smaller gamut would be compressed proportionally.
But what about the case where there are no colors near the boundary of the large space, but a few colors are present slightly outside the smaller gamut? Only a small amount of compression would be needed. If the compression began at the boundary of the larger color space, the formerly slightly out of gamut colors would be placed well inside the limits of the smaller space and saturation would suffer. From your answer, I would infer that in the hypothetical case, one would get better results from the use of a gamut just large enough to encompass all the scene colors. In this case, the ProphotoRGB space would not be optimal. Do you see what I mean?
Bill Janes
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I'm not sure I understand. The colors are where the colors are with respect to their chromaticity coordinates within the entire plot (human gamut). Obviously if they fall outside the gamut of working space A, that's a problem. If they fall within the gamut, the fall where they fall.
If you need them to now fit within the gamut of a much smaller working space (you need sRGB), the now fall where they fall depending on the rendering intent used to remap the colors.
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I'm not sure I understand. The colors are where the colors are with respect to their chromaticity coordinates within the entire plot (human gamut). Obviously if they fall outside the gamut of working space A, that's a problem. If they fall within the gamut, the fall where they fall.
If you need them to now fit within the gamut of a much smaller working space (you need sRGB), the now fall where they fall depending on the rendering intent used to remap the colors.
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What I was concerned about is addressed in this post:
[a href=\"http://www.steves-digicams.com/techcorner/July_2005.html]http://www.steves-digicams.com/techcorner/July_2005.html[/url]
My concern was that by using an excessively wide gamut space, saturation would be comprised when using perceptual colorimetric rendering with relatively small gamuts.
According to the cited article, the amount of compression used is up to the maker of the profile, and in most cases the entire larger gamut (starting at its boundaries) is not simply smashed down to the size of the gamut of the printer.
Bill Janes
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According to the cited article, the amount of compression used is up to the maker of the profile, and in most cases the entire larger gamut (starting at its boundaries) is not simply smashed down to the size of the gamut of the printer.
Bill Janes
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With the perceptual rendering intent, the creator of the profile can use any method they wish. If you profile the same device using the same instrument and patches but build it using two packages, you'll almost always end up seeing difference in output using Perceptual.
In theory, Colorimetric should match but that never happens either. But Perceptual is all over the map.
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The compression will take place at the boundaries of the image gamut as you should see in the screen dump I placed in my last post. Hopefully you can see that there are colors that are not at the boundaries of the larger triangle. Some may be, some may not be but the area where a color lies in the chromaticity diagram is where the mapping starts. Does that answer the question?
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According to this post, the compression usually does NOT take place at the boundaries of the image gamut, because the CMM does not take into account the image gamut, nor does it take place at the boundaries of the larger color space.
[a href=\"http://www.steves-digicams.com/techcorner/July_2005.html:]http://www.steves-digicams.com/techcorner/July_2005.html:[/url]
"Some misinformation on the web would lead you to believe that because the CMM cannot account for image gamut, that it simply compresses the entire gamut of the color space used by the image so that it fits inside the printer's gamut. This is, however, also not true. "
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Unfortunately, you still have not answered my original question. If you are using ProphotoRGB with a moderately sized gamut image and printing to a relatively smaller gamut device using perceptual rendering with a table based profile, does the gamut compression occur for the entire ProphotoRGB gamut or only to the extent of bringing the out of gamut colors into gamut?
The latter instance would require a "smart algorithm" that actually looks at the contents of the file to determine the extent of compression required, whearas the former would simply squash down the whole ProphotoRGB gamut.
Bill Janes
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The whole idea of perceptual is to prevent gamut clipping and thus to maintain a distinction between out-of-gamut colors. This means that image colors are shifted towards the center of the xy chromaticity diagram. To make room for out-of-gamut colors, some in-gamut colors must move too.
The extend to which in-gamut colors are compressed depends on the algorithms used by the profiling software. As there are no icc specifications for the perceptual rendering intent, the implementation is vendor specific -> proprietary algorithms.
There a many methods of gamut mapping. The difficult thing with gamut mapping is to account for the differences in shape of source and destination spaces. An additional problem is: What does the profiling software know about the source space of an image? It has to make some assumptions regarding this source space/colors.
Perceptual rendering applies the same gamut compression to all images, even when the image contains no significant out-of-gamut colors. As Mike Chaney writes "No smart CMM" yet.
Herman
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The whole idea of perceptual is to prevent gamut clipping and thus to maintain a distinction between out-of-gamut colors. This means that image colors are shifted towards the center of the xy chromaticity diagram. To make room for out-of-gamut colors, some in-gamut colors must move too.
The extend to which in-gamut colors are compressed depends on the algorithms used by the profiling software. As there are no icc specifications for the perceptual rendering intent, the implementation is vendor specific -> proprietary algorithms.
There a many methods of gamut mapping. The difficult thing with gamut mapping is to account for the differences in shape of source and destination spaces. An additional problem is: What does the profiling software know about the source space of an image? It has to make some assumptions regarding this source space/colors.
Perceptual rendering applies the same gamut compression to all images, even when the image contains no significant out-of-gamut colors. As Mike Chaney writes "No smart CMM" yet.
Herman
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In the absence of a smart CMS, photographers will have to assume more responsibility for the rendering of out of gamut colors. Perceptual rendering may be helpful in many cases, but, since it does not take the image contents into account, may not give the intended results and manual tweaking may be needed.
In an old post, Bruce Fraser gives some advice:
[a href=\"http://www.creativepro.com/story/feature/8582.html]http://www.creativepro.com/story/feature/8582.html[/url]
He briefly discusses tweaking an out of gamut Dahlia in his Color Management book.
Here is another post explaining how to use Hue and Saturation in Photoshop together with the gamut warning view to tame out of gamut colors:
http://www.udel.edu/cookbook/scan-print/ga...mut-huesat.html (http://www.udel.edu/cookbook/scan-print/gamut-hue-sat/gamut-huesat.html)
Bill Janes