Choice of Color Space

I shoot RAW then process them to JPEGs in the sRGB color space, as that is the

color space required by the printer I use. Until recently, I used the 16-bit

sRGB color space for my RAW processing (in ACR), believing that it made sense

to work in the color space which was my ultimate destination. (I save my RAW

files so I can re-process the images if new printer technology becomes

available.) Having read arguments in favor of larger color spaces, a few

weeks ago I decided to process all my new RAW files in 16-bit ProPhoto, then

convert to sRGB when saving as JPEG. Today I find this article:

 

http://www.jeremydaalder.com/singleArticle.php?articleID=6

 

The author points out some issues that originally caused me to resist ProPhoto

(for instance, why work in a color space you can't see and can't print?), and

concludes that you should use the smallest color space that will hold your

image. He argues that the disadvantages of ProPhoto (posterization, poorly

mapped colors, etc.) usually outweigh the advantages, which he appears to

believe are few and far between.

 

The argument that you should use the smallest color space which will hold your

image makes sense to me. My question is this: if your ultimate color space

destination is sRGB, but sRGB is too small to hold your image, are you better

off dealing with the sRGB clipping by working in sRGB from the beginning, or

should you choose a color space that will hold the image, then convert to sRGB

after your post-processing is completed?

 

Thanks.

The posterization only comes if you're doing ProPhoto as 8-bit. Do it as 16-bit, then you won't run into it. Or, as even the anti-ProPhoto Mr. Daalder puts it,

 

"Converting from RAW into ProPhoto makes some sense, as you will likely not run into ANY significant clipping issues. "

 

I think it's funny how he says that ProPhoto is "HUGE!" over and over. Huge? It's about the same as the human eye, and about the same as what Canon (and likely other) dSLRs can capture, if I recall. That doesn't seem so excessive to me.

 

I haven't gone looking for photos of mine that exceed the sRGB or aRGB color spaces, but I am still aware of at least one that does so significantly. Because I converted the RAW file into ProPhoto, I have at least some ability to decide and control what happens to those out-of-gamut colors. Had I not imported into ProPhoto, that would not be the case.

 

My philosophy is to store as much information as I can, and decide what to do with it later. Early on, I made the mistake of throwing away information (be it deleting photos, destructive editing, etc.) in the hubris of thinking that my decision that day was the "one true path", only to regret it later.

 

steve

<p>Excuse me, but this "author" doesn't know what he's talking about. An explanation follows:</p>

 

<p>It is not only your output that determines your working space but also input. If all your input is sRGB (say from a digicam that has no RAW mode), and if all your output is also sRGB (say a minilab printer), then fine, use sRGB as your working space.</p>

 

<p>But when your input is larger than sRGB (input devices such as scanners and digital cameras with RAW mode can capture a huge range of colors), and even when your output is still sRGB, the question becomes more complex. First of all, we are often interested in "storing" a bigger range of colors than the printer can output, just so that we would be able to use them when better printers with better inks come out or when those LED displays finally become commonplace. But even if you are not interested in "storing" colors for the future, you still need a large enough working space so that you can handle large input colorspaces. Why?</p>

 

<p>To answer this, read <a href="http://www.creativepro.com/printerfriendly/story/12641.html">this article</a> which compares different rendering intents available in Photoshop. As you will see, the difference between perceptual and relative colorimetric intents is that in the former, gamut compression occurs, while in the latter, only the "tails" of colors that are outside the destination colorspace are compressed, resulting in visible "clipping."</p>

 

<p>Why do you need to know all that, you may ask? Because in Photoshop, no matter what your Color Settings are set to, the default rendering intent on input is Relative Colorimetric. Additionally, most LUT-based input profiles have only one A2B look-up table which supports only one rendering intent. This means that when you convert from input space to your working space, you will get gamut clipping when the colors in your source gamut fall outside the range of destination gamut. Take a picture of any colorful flower (or a sunset shot), process it with ACR, and you will see why big spaces like ProPhoto are recommended by many as the working space to use even when the output space is much smaller.</p>

If you <b>know</b> you will <b>never</b> print or display on a medium with more than an sRGB gamut, work in sRGB. Otherwise, work in the smallest space that will fit your image.

<p>To quote the original article: <i>Certainly, in volume terms, they are ALL pretty much smaller than even AdobeRGB. This includes - Lightjets, Lamdas (see Figure 5), Thetas, Pegasusses (Pegasi?), Canon, HP and Epson inkjets (see Figure 4), Dye Subs, and You-Name-Its. Not one of them has a gamut larger than AdobeRGB in total.</i></p>

 

<p>That's not exactly correct. The figure below shows a nice big patch of greens and blues that my Epson R2400 can produce with K3 inks on Premium Luster paper. They fall well outside of Adobe RGB (colored with red).</p>

 

<center><img src="http://www.eugenescherba.com/files/colors.png" ></center>

Interesting, Eugene. But will the blue/greens also fall outside of Pro? I am new to my 2400 as I have been a dye guy for years (Epson 7600 dye and 1280). That seems pretty extroadinary that the 2400 printer could do that!

Steve, you've got to check out pigment inks! Here are comparisons of third party MISPRO

inks on an Epson R220/Epson Premium Glossy with aRGB and ProPhoto RGB. Even with the

Prophoto you can get beyond the space with green and blue, and way beyond monitor space.

You do have to be really careful to not get colors that are way out of context.<div></div>

Thanks for the information, everyone. My conclusion based on your information, my reading, and my observations is that in fact I should do my post-processing in the sRGB color space if I know the ultimate destination is sRGB. Here's why I have concluded that. First, I save my RAW files so I can always process them in a different color space if in the future I can print with a larger color space. Second, if the conversion to sRGB occurs at the beginning of my post-processing work, then I can observe and attempt to address clipping which may occur. For instance, comparing the sRGB and ProPhoto color space with the same RAW files, often more clipping occurs in sRGB, but sometimes I can reduce that clipping through exposure and contrast adjustments. However, if I were working in the ProPhoto color space then converting to sRGB as a last step, I would not know about the correctable clipping during my post-processing work, and so would not know to attempt to address it. In my case, then, it seems ProPhoto would be an advantage only if I were willing to save a 16-bit TIFF in ProPhoto, then convert that TIFF to an sRGB JPEG copy for printing purposes. Because I already save my RAW files, and TIFF files from my camera (1Ds2) are enormous, I am not willing at this point to save both RAW and TIFF files. Is my logic actually logical, or if sRGB is the ultimate destination (for now), is there still an advantage to converting to sRGB as a final step rather than a first step, where you also save your RAW files?

 

Thanks again for your help.

After messing around for a while with ProPhoto, here's why I chose the middle ground with AdobeRGB:

 

1. Very few images from my 20D have fallen outside AdobeRGB - mainly images with super saturated colours (reds/magentas and yellows particularly).

 

2. When I convert these files to one of my Epson R1800's ICC profiles, I encounter extremely bad colour channel clipping - and even worse if I convert to sRGB.

 

2. My Epson R1800 seems a good fit with AdobeRGB - converting an image fron AdobeRGB to one of my printers ICC profiles almost never results in colour channel clipping.

 

4. Even if there are current printers who's gamuts are potentially larger than AdobeRGB, what's the point as you are still limited by the paper anyway.

 

5. If output devices/paper in the future do greatly exceed AdobeRGB and ProPhoto would prove to be the best option, I still have the RAW files and I can re-process them into any colour space i feel like.

 

I'm concentrating on getting the best prints I can with the equipment I have RIGHT NOW. I'm not thinking about what may or may not be around in the future. For me AdobeRGB is the ideal middle ground between sRGB and ProhotoRGB, so that is what I use.

<i><p>However, if I were working in the ProPhoto color space then converting to sRGB as

a last step, I would not know about the correctable clipping during my post-processing

work, and so would not know to attempt to address it.</i></p>

 

<p>There would be no clipping at all if "Perceptual" rendering intent was selected.</p>

<p><i>Very few images from my 20D have fallen outside AdobeRGB - mainly images with

super saturated colours (reds/magentas and yellows particularly).</i></p>

 

<p>It's interesting that you came to this conclusion. You mean you are not interested in

preserving saturated reds/magentas/yellows? Wonder what you are shooting then...</p>

"There would be no clipping at all if "Perceptual" rendering intent was selected"

 

Wrong.

 

"It's interesting that you came to this conclusion. You mean you are not interested in preserving saturated reds/magentas/yellows? Wonder what you are shooting then..."

 

Correct. I am not interested in preserving colours I cant actually print. Like I said, I want to make the best of what I have now. With ProPhoto, make a couple of contrast and saturation adjustments, colours that were only just outside of AdobeRGB are now WAY outside. AdobeRGB is just easier to manage.

 

I'm not here to argue - I'm just here to give my opinion on why ProPhoto does not (currently) work for me. Everybody's needs are different and if ProPhoto works for you, then fine. There are people who argue for ProPhoto and against ProPhoto - but no-one argues against AdobeRGB. There's a reason for that.

Ricky, I believe it is true that there is no clipping with perceptual, but there can be desaturation. As I understand it, perceptual compresses the larger color space to fit the smaller color space, so out-of-gamut colors are not clipped, but in-gamut colors are compressed as well and may thereby be less saturated. Basically, you need to choose your rendering intent based on the nature of your image; in some cases, perceptual may be better, in others, relative may be better. I believe when bringing a RAW file into ACR in a space smaller than ProPhoto, Photoshop uses relative to convert to the smaller color space. This leads to the contention that whether you convert bringing the image into ACR or at the end of post-processing results in essentially (even identically) the same image, at least if you convert using relative. I can see where this is true if the images are processed exactly the same, but my experience has been that I can sometimes reduce clipping in sRGB through ACR -- clipping I would not have observed in ProPhoto, so that my post-processing work would have been different. So, I assume, the end result would not be the same -- it would arguably be better by having started the process in sRGB. Meanwhile, perceptual worries me if it may reduce the saturation of in-gamut colors. It strikes me that choosing between perceptual and relative adds another complication which could be avoided by working in sRGB. I am not trying to argue in favor of sRGB as a working space; rather, I want to obtain the best and most predictable image quality while still maintaining a relatively efficient workflow appropriate for an amateur like me.

Converting an image from ProPhoto to a smaller colour space using Perceptual often will still result in colour channel clipping. I know this because I've done it with my own files!

 

To quote Bruce Fraser:

 

"Perceptual rendering attempts to compress the gamut of the source space into the gamut of the target space. Exactly how this is accomplished is left to the discretion of the tool used to build the profile, but typically perceptual rendering desaturates all colors to bring the out-of-gamut colors into the target gamut while more or less maintaining the overall relationship between colors."

 

Note the use of the word 'attempts'. With ProPhoto sometimes colours are so far out of the gamut of the target colour space that mapping these colours to the target AND maintaining the overall relationship between colours is impossible - and clipping occurs.

<p>Ricky, you and Bruce are talking about apples and oranges

here.</p>

 

<p><i>Exactly how this is accomplished is left to the discretion of

the tool used to build the profile</i></p>

 

<p>"Discretion of the tool used to build the profile" line means

that Bruce is talking about LUT profiles with A2B0 tables that often

have only one such table for only *one* rendering intent built-in.

Conversion between ProPhoto and sRGB does not involve LUT tables.

Normally you get "0" or negative numbers for any of the channels

with absolute colorimetric conversion, but this is where Perceptual

intent comes in. BTW, Bruce recommends ProPhoto for most tasks in

16-bit, with the only exception being for very specialized ones or

8-bit pathways.</p>

<p><i>I believe it is true that there is no clipping with

perceptual, but there can be desaturation.</i></p>

 

<p>True. You can have colors that are (a) saturated (b) with no

clipped channels, and © in a small colorspace like sRGB. Pick

two.</p>

Two things:

 

 

1. My store has a Noritsu 2901 digital printer that prints with teeny-tiny LEDs and a newer 3213 machine that prints with a laser. Both machines balk at files that aren't 8-bit.

 

 

Consequently, if I know my output will be making C-prints with these machines, I'll shoot in sRGB or scan to get 8-bit files. A huge color space wouldn't do me much good for purposes of these machines.

 

 

2. For home printing, I've been pleased with Adobe RGB. For instance, this image of a dog and her toy was taken with a D100 in Adobe RGB. My Epson 2200 renders the bright yellow and day glow orange in the toy perfectly. So far at least, I haven't run into a color image shot or scanned in Adobe RGB where I've had trouble reproducing a crucial color.<div></div>

<p><i>For home printing, I've been pleased with Adobe RGB.</i></p>

 

<p>Adobe RGB is an excellent choice for a working space. I am not

arguing against it; I am just trying to make it clear that ProPhoto

RGB is not *inherently* bad just because it is bit. ProPhoto is also

an excellent choice, particularly for 16-bit imagery, even when the

palette of colors is small.</p>

 

<p>For nitpickers, by "saturated" in my post above I

meant "colourful" as defined by CIECAM02 specification.</p>

I played around a little with raw converter and converting raw files to the different color spaces.

 

I had been using AdobeRGB until I read Bruce Fraser's _Real World Camera Raw_. He recommended using ProPhotoRGB, which I've been doing ever since. 16-bit.

 

What I found by turning on the shadow/highlight clipping is that sRGB clips significantly more than ProPhotoRGB. Not a big surprise. These are normal pictures. Inside. Outside. Pictures of children, mainly, because that's what my last few sessions have been. I'll try some average wedding pics after this weekend. I'm not traveling to the Amazon rainforest to take shots of exquisitely saturated flowers under a brilliant sunset. Nor anything with a huge contrast range. ProPhotoRGB holds all but a few of the brightest highlights. AdobeRGB holds a few less highlights. sRGB clips not only more highlights, but also starts clipping yellows and reds.

 

I've heard that I should use the smallest color space that can contain my raw file. I've heard that I should just use ProPhotoRGB. Based on my experience, both can be true at the same time. Anything smaller than ProPhotoRGB clips additional highlights. Not a huge deal. Probably wouldn't even notice by the time I make a print. But why throw away information before I even start?

 

I'm still learning about this whole idea of colorspace, so don't take anything I've said here as being fact. I could very well be coming to the wrong conclusion. If so, please enlighten me. Thanks!

 

 

Eric

Joseph Holmes provides a number of working spaces to address some of the problems being discussed. Specifically addressed is the size of the working space vs. the range of 'useful' color it contains. Joseph provides his working spaces in several different sizes. See http://www.josephholmes.com/profiles.html .

 

I have been using his free working space (Ekta Space PS 5) for a year or so. It seems to work well for my uses and I'm thinking of buying one of his packages, probably DCam 3.

Eugene, it sounds like ProPhoto is an excellent choice if you work with images that exhibit problem colors that Adobe RGB would clip AND if you are going to follow through with profiling and a printer that would allow you to take advantage of the increased color range.

Yes, Eric.

Eugene, et al., since I do not know enough to know who is right, could you guys at least give me your opinion on this treatment of this topic?

 

http://www.luminous-landscape.com/tutorials/prophoto-rgb.shtml

 

At this point I am frankly just trying to be able to understand what you guys are talking about. Are there other sources that would be helpful to persons who have no real technical knowledge on these issues?

 

Thanks.

 

--Lannie

<p>Michael Reichmann's article mostly gets it right, but there are

two fine points to note:</p>

 

<p>First, the problem with what he calls "science-fiction" colors is

greatly exaggerated. In fact there is no problem at all thanks to

Photoshop's wonderful ability to map ProPhoto colors into monitor

colorspace for display. Whatever you do to the file that makes it

look wrong in ProPhoto will also make it look wrong in any smaller

colorspace (I am talking about 16-bit here). You can get "science

fiction" results with any colorspace, whether its sRGB or AdobeRGB

or ColorMatch. Again, thanks to Photoshop working-space-to-display

gamut mapping and monitor Proof Setup capability, this "science

fiction" problem only rests in Mr. Reichmann's mind.</p>

 

<p>Second point. Michael Reichmann states: <i>"But, on the other

hand, an image file in a wide space such as ProPhoto RGB needs to be

kept in a cage, so that it doesn't accidentally get into the outside

world. Anyone receiving a copy of such a file who doesn't know what

they have, and who doesn't function in a properly colour managed

workflow, or who presumes that the file is sRGB, can inadvertently

use it to produce some really horrid results."</i></p>

 

<p>I have my own opinion on this. First of all, a file in *any*

colorspace other than sRGB must be kept "in a cage," so what's the

problem? Second, when you get a color mismatch with

ProPhoto, you *definitely* know something is wrong, but when the

same happens with AdobeRGB, you sometimes know you got it wrong, and

sometimes you can't tell until you print the file, when it's too

late. So in this sense, ProPhoto is great for those who only started

understanding color management: when there is a mistake, you see it

clearly.</p>

Eric Merrill, my experience parallels yours, and is why I started this thread. Frequently I see clipping in sRGB which disappears in ProPhoto. This argues in favor of using ProPhoto. However, my printer requires sRGB. (See Eric Friedmann's last comment -- I cannot take advantage of ProPhoto's wider gamut for printing.) When I convert to sRGB, whether at the beginning or the end of post-processing, it seems I have two choices: use relative colorimetric, and the clipping returns, or use perceptual colorimetric, and risk desaturation of colors. Therefore, I believe it is correct to say, if your ultimate color space destination is sRGB, that working in ProPhoto just delays the clipping or desaturation which may occur. So, my conclusions are (1) save RAW files so you can later exploit a larger color space if desirable; (2) if you don't shoot in RAW but still post-process your images, shoot JPEGS in the largest color space available with your camera, and save that original; and (3) do your post-processing work in the color space which is the ultimate destination for that image. I believe (3) is the correct choice because sometimes, through exposure, contrast, and brightness adjustments, I can (at least in ACR) reduce or eliminate the clipping which occurs in sRGB. If I were working in a larger color space, I may not be aware of that clipping, and therefore would not know to attempt to address it. However, you may (wisely, perhaps) choose to do your post-processing in the largest available color space and save that as an original before converting to a smaller color space for printing if you do not care to duplicate your post-processing in the future when larger color-space printing may become available. My thought on that last point is that any image I return to later for potentially better printing will presumably also deserve a second effort at post processing.