I'm writing this post in response to a particular question on the Australian Photography Forum, but it's a question I see asked everywhere I go.
"What colour space should I work in?"
Such a short question, but with such a complex answer. There's no way I can cover every aspect of this matter - heck, there's been whole books written about it - but I hope I can give a bit of guidance. There are so many variables to consider, and ultimately, personal preference plays a big part. (I'm going to try to keep this brief, but I bet I don't! And I'm going to try to keep it objective, but I bet I don't do that either!)
Let's look at the main contenders:
sRGB: As far as I know, the "s" stands for "standard" ... well, if it doesn't, it should. (In my view, it could also stand for "safe" and "sensible".) It's an approximation of the gamut of the "average" imaging device - monitors and printers. In truth, the devices upon which the standard was modeled have long since been superceded, but the standard remains reasonably sound. sRGB is the required colour space for the internet, and for all consumer print labs (and some pro ones).
Adobe RGB: This is a slightly bigger gamut, and is probably the "standard" of the future. At the moment only the very high-end monitors have a full Adobe RGB gamut, but I guess more and more will achieve it. The really good inkjet printers achieve a fair slice of Adobe RGB, and even exceed it in some colours.
ProPhoto RGB: This is a ridiculously big colour space that (I think) encompasses all visible colour. Needless to say, it far outstrips the colour reproduction capabilities of any monitors or printers currently available.
How do you choose your colour space?
Well, if you shoot in Jpeg mode, you choose it in the camera (ProPhoto isn't available). If you shoot Raw, you choose it in your raw processing program.
How do you choose the right one for you?
Well, I want to start by very firmly saying this: If you have no experience in colour management, use sRGB. I don't care what you read in a book, or saw on a forum, or some bloke told you at the pub. If you don't know the basics of ICC profiles and the conversion thereof, dabbling with the larger colour spaces will end in tears.
sRGB is your best friend. If you use sRGB throughout your workflow, you don't have to think at all. Like I said, the "s" stands for "safe".
Having said that, a little knowledge about colour management is easy to come by. There's plenty of good books and sites about it.
Ok, assuming you understand the basics of profile conversion, how do you choose the right colour space?
Well, there's two ways of looking at it:
(1) Choose the space that's relevant for your current workflow; or
(2) Choose a "future-proof" space, ie one that allows you to take advantage of potentially bigger gamuts of the imaging devices (monitors and printers) that you might have access to in the future, assuming you want to re-visit your old photos at that point.
In order to help you make that decision, let's break down your workflow into the relevant parts.
Part 1 - what you're shooting
Let's get something damn clear to begin with - sRGB is not a "small" colour space. The average portrait or landscape photo has a colour range that fits nicely within sRGB. I'd estimate that 80% of photos that 80% of people take don't have colours that exceed the limits of sRGB.
However, you don't have to look far to find subject matter that has colours too bright for sRGB. Sunsets, for example. Those brilliant orange skies are likely to cause Red channel clipping in sRGB. Bright floral photos will do it, too. Etc etc.
This is a good time to reiterate the importance of shooting in Raw. If you're not, I encourage you to start doing so. Raw capture allows you to choose a colour space that suits the photo, and/or manipulate the colour gamut of the photo to fit the chosen space. In short - Raw is awesome.
So, here's your first consideration. Think about what you shoot, and whether you're capturing super-bright colours.
Part 2 - the screen you're editing on
So many people forget about this when they're choosing a space. What's the point of choosing a larger space if you can't see it??? As I said earlier, there are more wide-gamut monitors becoming available, but a heck of a lot of us are still using regular-gamut monitors. (I've invested in a small Eizo monitor that cost more than my first car, and it's a brilliant bit of gear, but it doesn't exceed the sRGB gamut.)
If you're using a regular-gamut monitor, there's no point in saturating colours out of sRGB, because the screen will just stop showing you an accurate representation of them. And once you're editing colours you can't see, you're asking for trouble.
I've written a long and eye-wateringly boring article related to monitor gamut here, if you're interested.
Part 3 - the end result
At the end of the day, you take photos to show people.
Any photos that go on the web must be sRGB - there's no debate about that. sRGB is for web.
Printing might be different. The average lab will reproduce sRGB adequately, but may not be able to go much bigger in gamut. But of course it depends on the calibre of the lab you use, and the type of media you print on. Prints on canvas will have a different gamut to prints on Lustre paper, which will be different again from prints on Metallic. And RGB prints will differ from inkjet prints.
I can't give more advice than that. You really need to consult your lab and find out their specific advice and requirements. Some might even give you their actual print profile with which to soft-proof and see exactly what gamut you've got to play with.
Ok, with all that in mind, let's go back to the two options I gave you earlier.
Option (1): Choose the space that's relevant for your current workflow
Let's say you shoot bright things, and even have a wide-gamut monitor, but only show your images on the web. What's the smallest gamut in that equation? sRGB, for web. So there's no benefit of working in a larger space.
But what if you shoot bright things, and have a wide-gamut monitor, and show your images on the web, and print them on your wonderful wide-format Epson printer? Well, that's different. You want to be working in a bigger space that takes advantage of the Epson inks, then converting down to sRGB for the web.
Ok, how about if you shoot bright things, but just have a regular-gamut monitor? Well, you've got to choose the space that you can see when you're editing, so that would be sRGB. Frankly, it doesn't matter what output you choose.
And lastly, if you only shoot "normal" colours (portraits etc), then just make it easy for yourself and choose sRGB. You don't need that extra colour gamut, so why bother?
I hope this makes sense.
Option (2): Choose a "future-proof" space, ie one that allows you to take advantage of potentially bigger gamuts of the imaging devices (monitors and printers) that you might have access to in the future, assuming you want to re-visit your old photos at that point.
If you're a forward-thinker, this option is for you.
If you are editing photos and thinking "I'm going to save up enough money for one of those amazing inkjet printers and a wide-gamut screen, then I'm going to print this baby, and it's going to look AMAZING!" ...
... or, if you think "This Adobe RGB Epson printer is great, but I bet in a few years Epson will develop new inks that are even brighter, and I wanna piece of that!" ...
... then you should be working in a suitably large colour space to satisfy your future self.
(Please note, if you're editing in ProPhoto RGB, you must work in 16-bit mode in Photoshop. Otherwise you're likely to get banding.)
Well, if you've read this far without falling asleep, you're amazing. I hope some of it made sense, and that it helped a little. All comments and criticism welcomed.