Another stupid CM question

[SteelD]

OK, so AdobeRGB has a wider gamut than sRGB. Web/screen display uses sRGB and printers use AdobeRGB. Is that right? How do we know that a printer has a wider gamut than a screen? Is this assumed from knowledge that ink on paper has this capability or is it something in the printer specification?

In other words, if a buy an Epson 3800, will I get better images by using AdobeRGB thoughout even though the image looks muted on-screen because it is clipped by the monitor?

[bez]

I’m no expert so perhaps should keep quiet, but I don’t think it’s quite right to say printers 'use' Adobe RGB. In this sense they are colour blind, and will print whatever is sent to them by the application, within the limitations of their ink set.

It’s hard to accurately compare transmitted light (monitor) to reflected light (print) and the two are rarely exactly the same.
So if anything I think it’s the other way round – a good monitor is capable of displaying colours any particular printer can’t reproduce (hence the gamut warning in Photoshop soft proofing) and because they’re transmitted light, will generally look 'brighter' than a print.

[SteelD]

I’m no expert so perhaps should keep quiet, but I don’t think it’s quite right to say printers 'use' Adobe RGB. In this sense they are colour blind, and will print whatever is sent to them by the application, within the limitations of their ink set.

Maybe I should have made my question a bit clearer. How do I know that a given inkjet printer has an inkset capable of support a gamut wider than, or at least the same size as, AdobeRGB?

So if anything I think it’s the other way round – a good monitor is capable of displaying colours any particular printer can’t reproduce (hence the gamut warning in Photoshop soft proofing) and because they’re transmitted light, will generally look 'brighter' than a print.

I thought that a monitor had a very limited gamut hence their support for sRGB and that a printer can reproduce a wider gamut than a monitor.

Maybe somebody can point me to a source of 'colour management made simple' I don't need the history or an in-depth explanation of what it all means just what I should use where.

Thanks

[Costas L]

I thought that a monitor had a very limited gamut hence their support for sRGB and that a printer can reproduce a wider gamut than a monitor.

What you say can be true depending on the specific monitors and printers you have in mind. An old very cheap basic monitor might well have a more limited gamut than a one of the new range pro quality printers from Canon and HP which exceed the sRGB gamut. But this is not generally true, quality monitors designed for image display approach and in some instances exceed parts of the AdobeRGB gamut.

This has nothing to do with colour management, you just need to look at the specifications of the screens and printers you are interested in and compare their gamut with the one your interested in. For monitors, start with these 2 - check percentage of NSTC gamut a monitor covers, you will also find info on these on other posts.

Dell Ultrasharp 2407WFP-HC
NEC MultiSync LCD2690WUXi

[SteelD]

Thanks for that Costas though I wouldn't know what figures to look at or what they mean. Let's be specific - I plan to buy an Epson Pro 3800 so I assume that that has a reasonable gamut and would support AdobeRGB.

My monitor is an old iiyama Vision Master Pro 19" CRT so I doubt that that is very good and must be the next thing to upgrade (not now but sometime next year). I'll just have to live it for now (can't afford printer and screen in one go).

[DavidW]

Unfortunately there's no such thing as Colour Management Made Simple; it's a topic where trying to understand the nuances can help. That said, there's some excellent articles in the Tech Corner at Steve's Digicams. Look particularly at February 2005 for a start, then May 2005 if you use an Epson printer or June 2005 if you use a Canon printer. Other particular favourites are July 2005 on rendering intents and September 2005 on soft proofing - though I'd leave soft proofing for a while until you've assimilated the more basic stuff.


There are two sorts of profile; device independent, which are for mathematically defined abstract colour spaces, and device spaces, which characterise a real device such as a monitor or printer. Printer profiles are only valid for a particular printer / ink / paper / driver combination (though, in truth, changing driver versions doesn't usually affect things).

Files are best created and kept in device independent spaces with a few notable exceptions. The one that comes to mind is sending files to be printed by a bureau; often you have to apply the profile of the Frontier or similar device as these devices don't understand embedded profiles. You save the files without embedded profiles and send instructions to print without colour corrections. In essence, what you've done is used colour management on your machine to move the data to the device's own colour space, then told the operator to print your files with no further adjustment.

Some transformations are destructive - such as narrowing the bit depth (e.g. 16 bit to 8 bit) or changing the colour space of a file. If you have to do any of these, consider keeping a copy of the file before making these transformations, so that you can get back to where you were.


You hear a lot of talk about gamut - that's the range of colours that the profile can represent (if device independent) or the device can represent (if it's a device profile). One very important concept is that, by itself, colour management can't widen the gamut of an image; gamut is only lost via colour management. In other words, if your printer is capable of greens that are in Adobe RGB but are outside the sRGB gamut, you can only get those greens when printing an Adobe RGB file, because they can't exist in an sRGB file. It is possible to compare profiles by projecting gamut plots onto each other, but that can confuse rather than help. It depends on how your mind works.


The rendering intent determines what happens on transitioning from one colour space to another. For most photograhic purposes, you only need worry about relative colorimetric and perceptual. Absolute colorimetric has no place in a photographic workflow, whilst saturation is defined as being for items like business graphics, where you want bright saturated colours. However, some calibration solutions (I believe Printfix Pro is one example) use Saturation for their attempt to optimise photo printing.

In essence, relative colorimetric (which you should use with black point compensation on in almost every case) pins out of gamut colours in the destination colour space to the edge of the gamut. This gives good results if almost all your colours are in gamut in the destination colour space (as you can check using the Gamut Warning feature in Photoshop with the destination colour space selected in the proofing setup), but looks horrible if you have more than the merest hint of out of gamut colour, as you lose all tonality in the out of gamut areas.

Perceptual adopts a different approach; that compresses all the colours to avoid the 'out of gamut' effects of relative colorimetric. However, in doing so, it distorts your in gamut colours (by how much is not well defined at the moment). Perceptual is the safest choice for photographic work, but using relative colorimetric when appropriate can help.


Thinking of monitors as sRGB devices is rather out of date. sRGB is a reasonable approximation to an old CRT monitor. Modern LCD monitors, especially recent higher end models, have a significantly wider gamut than sRGB, including most or even all of Adobe RGB. You shouldn't set sRGB as the monitor profile for a modern monitor; if you have no colorimeter, use the manufacturer's canned profile plus Adobe Gamma or similar, though it's hard to get good results this way and a colorimeter is highly recommended.

sRGB remains the 'safe' option, not least for use on the web where very few browsers will use embedded profiles in images (at the moment, it's pretty much just Safari, though the upcoming Firefox 3 has colour management support on Windows and Mac OS X).


Modern digital SLRs used in RAW mode have particularly wide gamuts; there are colours that are in gamut even on older models that are outside the Adobe RGB gamut. This is why there's increased interest in using very wide gamut spaces such as ProPhoto RGB (which is used internally in Lightroom). These very wide gamut spaces must be used in 16 bit mode to avoid posterisation; in 8 bit mode, adjacent colours are just too far apart to represent smooth gradients. For that reason, if you want to turn a 16 bit file in a wider colour space into an 8 bit file in a narrower colour space, you convert it to the new profile then drop to 8 bit mode (and not the other way round!).

There are many potential pitfalls in using wider gamut spaces. As you've already figured out, you have colours in your file that can't be seen on your monitor. One way around this is to use screen profiles with gamut compression built in; essentially increases the degree of compression used for the perceptual transformation from the file to screen (screen profiles are invariably used with the perceptual rendering intent). Often an easier way is simply to be guarded if you make any radical transformations to the file; remember that there may be colours in your file that are out of gamut on your printer and your monitor.

The advantage of using wider gamut spaces is that you can preserve beautiful colours that you can print that are way outside narrower gamut spaces.



If you want some starting places, the most important thing is to get a good quality monitor and calibrate it with a good quality hardware colorimeter. Gamma 2.2 is standard for screen calibration, as is the use of D65 (or if you don't have D illuminants, 6500K). I'd take these as a starting place, except on a laptop screen where using the native colour point of the screen can produce better results. Laptop screens are almost invariably awful for colour critical work.

I would bring files into Photoshop from Camera Raw as 16 bit ProPhoto RGB. It's never got me into trouble; just be aware of the potential pitfalls. If you use a non-destructive workflow with adjustment layers, masks and the like, it can be possible to revisit the decision to use 16 bit ProPhoto later - especially if you're working in Photoshop CS3 with the RAW file as a Camera Raw Smart Object, and you're using Smart Filters, adjustment layers and masks only.

Remember that colour management can only ever reduce gamut by itself, not expand it. If you use even Adobe RGB at this stage, you are throwing away some colours that your camera can capture, though, to be fair, those losses may well not be significant. You can always delay the decision to throw away those colours, but once they're gone, they're gone. If you must use 8 bit, use at most Adobe RGB; as I explained earlier, ProPhoto RGB has such a distance between adjacent colours that you must use it in 16 bit mode.


Files for the web should be 8 bit sRGB - convert to sRGB first, then 8 bit. Don't lose the original file, as both transformations are destructive. In Photoshop you can use Image -> Duplicate (or the New button in the History palette) to avoid getting into a situation where pressing Save will overwrite your original.


For printing, use the best profiles you have for the printer / ink / paper / driver combination you're using. If possible, use the application to manage colour and tell the printer driver that's what you're doing. The main reason this isn't possible is when printing monochrome; in that case, you usually have to let the driver do the colour management.

The gamut warning feature in Photoshop can help you choose a rendering intent, and soft proofing can help you tweak the image, but neither are a complete replacement for printing a proof. You can always print a smaller version of an image and/or print just tricky areas at full size first when trying to optimise the settings.

Be aware that different papers have different gamuts and properties. Glossy paper has a wider gamut than matt. When printing with profiles, you should use the same driver settings as were used to create the profile, especially for paper type. If you don't know the correct settings for a third party profile, ask.


Be aware that the illumination you use to view a print changes your appreciation of the colours, also that prints and on-screen display can never match perfectly because - amongst other things - your screen is emissive and the print reflective.


I hope this quick trip through colour management helps. I'm only recommending starting points, and these are my decisions for my workflow.

Understanding what you're doing can help you make wise decisions. If you're originating content on your machine, think about what you want to finish up with. If you need 8 bit Adobe RGB JPEG files and you're making little or no adjustments on your computer, it may be best to set your camera to Adobe RGB and shoot JPEG. (That said, it may be best to shoot RAW + JPEG; it never hurts to restrict your options).



David

[bez]

How do I know that a given inkjet printer has an inkset capable of support a gamut wider than, or at least the same size as, AdobeRGB?

I think it’s true to say there are colours in Adobe RGB the 3800 (or any inkjet printer) will not be able to reproduce.

When’s your book coming out DavidW?

[Costas L]

Thanks for that Costas though I wouldn't know what figures to look at or what they mean. Let's be specific - I plan to buy an Epson Pro 3800 so I assume that that has a reasonable gamut and would support AdobeRGB.

My monitor is an old iiyama Vision Master Pro 19" CRT so I doubt that that is very good and must be the next thing to upgrade (not now but sometime next year). I'll just have to live it for now (can't afford printer and screen in one go).

As Bez said - the 3800 is good in the gamut area.

I assume the monitor is calibrated, since without that your just wasting your time and ink and paper on the 3800. I do not think your monitor will be a problem unless you find the prints and screen do not match up too well, suspect biggest problem might be with shadow detail on old monitors.

[Kevgermany]

Comparing a printer's capability in percentage terms to a specific colour space is pretty meaningless. As was mentioned above, the capabilities are printer/ink/paper/driver related.

One needs to assess the performance in specfic colour areas, particularly the ones that affect your work.

One also needs to bear in mind that it's the overall appearance of the print that matters - not whether a colour is out of gamut or not. Unless you're going to be comparing prints side by side with others, you'll find most of the modern printers give good results.

Personally I find the reds and greens poor on my 2100, but it's an old model and hopefully the newer machines have improved on it.

Suggest you get some sample prints of your own images from Epson, although I don't think they'll really tell you the full story.

[SteelD]

Thanks for comments and thanks to DavidW for that detailed response (I've read it a couple of times and think I need to read it a few more times).

So, this is what I've now got:

Shoot in RAW. When importing into PS, check the out of gamut colors and adjust colour space i.e. if AdobeRGB still has out-of-gamut colour then open in ProPhotoRGB and then convert to AdobeRGB using a Perceptual rendering intent to bring colours within the AdobeRGB gamut.

The Epson 3800 should (from what I understand) have a pretty good gamut (even some AdobeRGB may be out) but it will be quite close.

So, if I profile my monitor (I've got an Eye One arriving today) and accept the fact that it isn't particularly wide gamut and that shadow detail isn't too good, keep my images in 16-bit mode and print to the 3800 using the ICC profiles provided for the respective papers I'll be using, then my colour-management process won't be too bad.

I hope that sounds about right.

(The water is becoming clearer but as it does so, I realise that there is more depth than I first imagined!)

[Kevgermany]

Your work flow sounds good, just watch for clipping, especially if you get tempted to edit/manipulate in Prophoto and start bumping up the saturation.

[DavidW]

If you want to project the gamut of one profile on to another and you use Windows XP, install the Windows XP Color Powertoy (if you can't find it, come back to me and I'll dig up a link). I believe the same features are built in to Vista.

There is software out there that will put the colour space of an image inside the gamut of a profile (these plots are typically drawn on Lab axes); that's probably the easiest way to visualise how well a device will manage to render a particular image - though you can do pretty well with the gamut warning and soft proofing features in a competent image editing program such as Photoshop. In any case, these results are only of any value if the profile is accurate.


The percentage coverage of a particular colour space is largely marketing guff - though it does matter in one important way. High percentage coverage of the NTSC colour space for the latest flat panels monitors suggest that those involved in video production can discard their expensive reference monitors and use a modern flat panel instead. Of course, this is irrelevant for a still photographer.

For people that do a lot of Adobe RGB work, then the more of Adobe RGB that's covered by your monitor, the better. However, high coverage is something to aspire to rather than being absolutely essential.

What really matters with any device is good coverage of the colours that you use, the device being well calibrated, and having a good profile.


On HP Advanced Photo Paper Glossy, my B9180 goes outside the Adobe RGB gamut in the yellow area (not awfully surprising, as yellow is a primary colour for a printer). It's also outside in parts of the magenta area (again, around another primary) and in the cyan towards green area (which largely reflects the cyan primary, with the greens being based on cyan plus yellow). For a shot of some daffodils, the B9180 may well make use of that coverage. For a head shot in the studio, it certainly won't!

No printer covers the whole of Adobe RGB; I'm not even sure that such coverage is even theoretically possible for a reflective device like a printer. The reason for suggesting using Adobe RGB (or a wider colour space) rather than sRGB is that modern inkjets have some significant areas of coverage outside sRGB. If you used sRGB for post processing, you've lost those colours from your file even if they were there in the RAW file.


The area where Adobe RGB is particularly wider than sRGB is in the greens (the main difference between the two is in the location of the green primary), which is an area I identified above as particularly strong in my B9180. The B9180 has some greens outside the Adobe RGB gamut; the same is true of other quality modern inkjets.

Consider a foliage shot taken with a modern DSLR in RAW mode. If you used sRGB in your workflow you may well lose a tremendous amount of green tonality that your printer could print. You'd keep all the tonality that the printer could print if you used a wide space like ProPhoto RGB.

A particularly nasty scenario would be to do most of your work on that shot in a wide gamut space, then convert to sRGB using relative colorimetric. You'd probably have a bunch of green colours pinned to the edge of the sRGB gamut; perceptual would have avoided this. Watch out if you're printing via a bureau that needs sRGB files and you start in a wider gamut space - the rendering intent you use to convert to sRGB matters! If all your colours were in gamut for sRGB anyway, relative colorimetric would produce a more accurate sRGB rendition, but with colours that are out of gamut for sRGB, relative colorimetric would be a disaster.


Kev's idea to get sample prints of your images is a good one, but I'd raise two provisos. Firstly, unless your current monitor is calibrated and profiled, what you understand the file to look like isn't likely to be what it actually looks like. You get used to the defective rendition of your own monitor.

A typical uncalibrated flat panel is set to far too high a colour temperature (that is, far too cool), far too much contrast and is excessively bright. If that's what you were used to looking at and you looked at your images on my well calibrated and profiled screen, you'd think your images were awfully warm, lacking in contrast and dull. My screen is showing you nearer the truth of the file, it's just not what you're expecting. This is why a good calibrated and profiled monitor really should be the starting point for any serious photographic work. Fortunately both a quality monitor and quality colorimeter setup are getting much cheaper.

I am using a Dell 2007WFP (S-IPS version; there's some PVA based ones out there which aren't quite as good) with Monaco OPTIX XR Pro. Some of the Dell panels are now available with the -HC backlight, which increases the gamut significantly and is worth having, though it wasn't available when I bought the 2005FPW (the 2007WFP superseded the 2005FPW; I got my 2007WFP as a warranty replacement for the 2005FPW). OPTIX XR Pro is now discontinued; when X-Rite, who owned Monaco, bought out GretagMacbeth, they only had room in their product range for one screen calibration solution, and they kept Eye One Display 2.


The second proviso is that you get used to the look of your own printer and the paper you use. It may well be far from ideal, and the newer equipment is producing technically better results, but you don't like it because it's not what you're expecting. This is akin to photographers liking the look of their favourite films. Velvia doesn't produce a technically perfect colour rendition by any means, but as a creative product, some photographers find it valuable.

The optimum sharpening and resolution differs from printer to printer anyway - that can take a bit of learning with a new printer.


Overall, the most important thing to remember is that photography is a visual art, albeit with a fair amount of science involved. It's not getting the most technically perfect print that matters, but the one that is most pleasing to the photographer (and his or her clients if it's a paying job!).


As for bez's comment - I'm humbled. I sat down and wrote my original post aware that a family funeral was about to start that I couldn't get to because of my chronic health problems playing up.

I figured that the best way to remember Richard was to do something useful, so I wrote about colour management. I'm glad that the post helped.



David

[gcrogers]

David (SteelD),
IMO, the best way to learn this stuff is to start doing it...slowly, step by step, and methodically. It sounds as if you're like me, you want to know what you're doing before you start. That is a tall order for color management.

I might suggest the following; (just FWIW)

1. Decide that you want to do this (apparently you already have....good for you).
2. Choose a colorimeter and get your monitor calibrated. Don't worry about monitor gamut for now. You'll find out soon enough if your monitor is good enough for you or not. (and if it's good enough for you is all that matters.
3. Pick a paper that you like and make sure it has a proven profile (for example, any papers from your printer OEM as long as it's mainstream (Epson, HP, Canon, etc.) Load the profile.
4. Now you can start learning and worrying about color spaces and such.

Regards,
Greg

[DavidW]

Shoot in RAW. When importing into PS, check the out of gamut colors and adjust colour space i.e. if AdobeRGB still has out-of-gamut colour then open in ProPhotoRGB and then convert to AdobeRGB using a Perceptual rendering intent to bring colours within the AdobeRGB gamut.

The Epson 3800 should (from what I understand) have a pretty good gamut (even some AdobeRGB may be out) but it will be quite close.

So, if I profile my monitor (I've got an Eye One arriving today) and accept the fact that it isn't particularly wide gamut and that shadow detail isn't too good, keep my images in 16-bit mode and print to the 3800 using the ICC profiles provided for the respective papers I'll be using, then my colour-management process won't be too bad.

I suspect most if not all CRT monitors still in use are getting very tired. The tubes have limited life; most reckon they're pretty useless after five years. Not only does the picture on a CRT go soft over time, the gamut reduces as well.

It may be that reaching for the Epson 3800 makes the most sense - but I do wonder if you'd be better replacing the monitor now and either settling for a lesser printer or continuing to save for the printer. The Eye One Display 2 should be able to calibrate and profile your old monitor, but significant errors may remain, the on screen image may be soft (I really wouldn't want to try to judge sharpness on an aged CRT) and the gamut rather limited. If you are working with a poor monitor, you don't know what your files really look like.

If you get the monitor profiled, I'd be interested if a copy of the resulting profile; I could compare it to that of my Dell 2007WFP and sRGB.



Shooting in RAW I agree with. I never shoot JPEG on a DSLR; the only reasons to shoot JPEG are high volume and/or maximum frame rate work (such as 'canned' portrait shoots when you know your settings and lighting well and are going to do limited post processing, and sports work especially when images need to be filed very quickly).


Why are you worried about bringing everything into Adobe RGB? Adobe RGB isn't a magic panacea, and it's likely to be narrower than your camera's gamut in various ways. Unless you have to deliver Adobe RGB files to someone, I'd stay in the widest possible colour space so that you can make the fullest possible use of your printer's gamut.

Every run through a colour management system distorts the image in some ways - whether it's clipping out of gamut colours to the edge of the destination gamut (relative colorimetric, narrowing transformation), compressing the gamut of the entire image (perceptual, narrowing transformation), reducing the effective number of colours in the image (widening transformation without increasing bit depth first) or something else.

The ideal is to make just two transitions - from the camera's colour space to your working colour space, then from that space to the printer's colour space when you print.


If the files are just for your own use, and you're happy to work in 16 bit mode (with the associated penalties in memory use, processor power required and file size), I'd stick with ProPhoto RGB. Do not use ProPhoto RGB in 8 bit mode. As Kev notes, you can get into trouble with ProPhoto RGB, especially if you make significant tweaks to an image, but if you're modest, you'll be fine.

One caution with ProPhoto RGB is that some parts of the ProPhoto RGB gamut are imaginary colours. For more on this see the Wikipedia article on Imaginary Colour. One way to get into trouble is shifting some or all of your image into imaginary colours, or colours so far from the gamut of your monitor that you have no real way of perceiving what is happening (and no way to print anything near to resembling the resulting mess).


If you need Adobe RGB, select Adobe RGB in the RAW converter. That way, the histogram is showing for the Adobe RGB workspace and you can adjust the image for Adobe RGB there. Adobe RGB can be used quite happily in 16 bit or 8 bit mode, though if you want to transform on to sRGB at a later point, 16 bit is recommended.

If you just need a quick sRGB file and that's all you need, why not set the RAW converter to 8 bit sRGB? You can always set a different colour space and tweak the settings there later for a wider colour space. That way, you can tweak the settings in the RAW converter using a histogram that's correct for sRGB.


As far as printing goes, the Epson 3800 is about as good as it gets in this bracket at the moment. There is the improved K3 with Vivid Magenta inkset higher up in the Epson range, but it's not available in the 13" or 17" bracket at present, and it's not a huge improvement overall. Epson will, of course, talk about a new departure in colour, complete with prints that make use of the extended gamut in the magenta area, but for many prints I think you'd struggle to tell the difference. As we've said at various points in this thread, it's not how wide the overall gamut of a device is that matters - it's how well it covers the colours you want to use.

There are slight differences between the manufacturers - but as Vincent found in the "Three Pigs" review, Canon, Epson and HP are overall pretty close.

Overall, modern inkjet printers are extremely good, and whilst there will continue to be improvements, I think it unlikely that these will be anything other than progressive small improvements from here on.



David

[Costas L]

High percentage coverage of the NTSC colour space for the latest flat panels monitors suggest that those involved in video production can discard their expensive reference monitors and use a modern flat panel instead. Of course, this is irrelevant for a still photographer.
David

Why so David ? I have been busy pulling together a nice system for video editing but the benefits are certainly flowing into my still photography as well. I have not updated the monitor yet, but I see getting one that covers a high percentage of the NTSC colour space will benefit both my videos and still images.

If your saying there is a lot of hype out there I agree, and when it comes to 95% of what we do, wide gamuts and contrast ratios are not relevant. Most images make an impact from how they look in the mid tones, but the other 5% are the ones with that little touch of magic where getting it right across the board can help.