The are three popular RGB working space profiles you could use in Adobe Photoshop’s – sRGB, Adobe RGB (1998) and ProPhoto RGB. If you look around the net you’ll find vehement arguments in favour of each of them and just as many listing their shortcomings. The truth is that there is no right and wrong answer to the question of which RGB working space you should use. I’ve recommended each of them to different types of customers over the years.
RGB working space choice is an important one though as too many Photoshop users limit the potential colour from their images by an injudicious selection, but likewise there are many who cause themselves extra hassle by slavishly following advice they don’t understand and creating colour workflow headaches they could avoid if they kept things simpler.
The choice of RGB working space is most important for photographers who use Photoshop to process their raw images, but it can also be important for designers, printers and retouchers and others. However, before we go to far into discussing the merits of different working spaces I should start with what a working space is.
What is an RGB Working Space?
The most common colour model used in computing is the additive RGB model. Red, green and blue lights are added together to make colours. Each channel of red, green and blue can have values from 0 to 255. If all three values are 255 then you have white. If all three are 0 then you have black. RGB is what’s known as a device dependent colour model. Key to what colour you end up with from any combination of R,G and B values are the actual colour of the red, green and blue primaries and also the tonal curve in each channel. If you go and look at all the TVs in an electronics shop they will all be showing the same pictures but each will look a little different from its neighbours. Each TV has a different colour space based on who makes it, the brightness, contrast and other settings, the back light and a host of other variables. The same is true for computer monitors, projectors and any other system that displays colour. All cameras and scanners also see colour slightly differently, just as all people do. So there are an infinity of RGB colour spaces as every RGB device has its own.
So, in order to give the RGB values in your image a colour meaning, to know how to represent the colour on screen and to know what change to do when you make an edit, your software has to know exactly what colour space it’s dealing with. Just knowing what the RGB numbers are isn’t enough because the same RGB values will result in a different colour in each colour space.
The files that give software the information it needs as to exactly what its dealing with are called ICC profiles. Most ICC profiles are made from measuring the colour capabilities of a monitor, printer or camera but some are created artificially by developers and programmers to be more generic. Adobe chose to call these generic profiles Working Spaces in their software. You will probably have dozens of RGB working space profiles on your computer, any one of which you could theoretically use to edit your images in. To bring some order to this chaos Adobe decided that it would suggest just a few different default RGB working space profiles to edit their files in. The key word there is default. It is possible to use one RGB working space for one image and a different one for the next so it’s not a once and for all decision. However, if there is a good reason for you to use one in preference to another then it make sense to set it as the default RGB working space just to make life easier for yourself.
Below I’ll outline the pros and cons of each of the three main contenders. There are a few other very good RGB working space profiles out there that have been designed for a particular workflow or type of work that are very good and worth considering if you really want to take things to a higher level but for most Photoshop users it comes down to a choice of the three.
sRGB is the smallest and oldest of the three common RGB working space profiles. Defined by Microsoft and HP in the 1990s to be a generic colour space similar to the colour gamut of CRT monitors then in use. It is very widely supported by anything from cameras and scanners to iPads and monitors, and is also the default RGB profile for many applications including Photoshop.
There are two big advantages to using sRGB. Firstly, it acts as as lowest common denominator. It’s a small colour space supported by lots of hardware and software so as you move data around it should look OK. Secondly, most web browsers assume an image is sRGB so it’s a good default colour space for any image going on the web. It’s also a great choice if you are working in graphic design or perhaps pre-press and just receive RGB files rather than doing your own photography because most images you’ll be getting will probably be sRGB.
The huge disadvantage it has though is that it has a much smaller colour gamut than the typical range of colours that can be captured by digital SLR and medium format cameras, and smaller even than many good inkjet printers. So if you convert raw camera files into sRGB you could instantly throwing away lots of colour that the camera has captured, and when it comes to print you are missing out on colour that could be printed.
I’ve read many articles and talked to many customers that ask why they should change from sRGB to one of the bigger RGB colour spaces. For some there is no good reason why they should but, especially amongst photographers, there is the assumption that their data is somehow naturally sRGB and it’s tinkering to change it to something else but actually the reverse is true. Digital camera images are captured in much bigger colour spaces and artificially reduced to sRGB by default in many applications.
Adobe RGB (1998)
Adobe RGB was specifically designed have a colour gamut that encompassed commercial printing presses and is larger than sRGB. But, it is still smaller than the range of colours that cameras may be able to see and now that printing technology has moved on there are areas of colour where Adobe RGB could be limiting your output on professional quality inkjets. It’s main advantage is that it is bigger than sRGB so you throw away less colour from the camera and can print more. Also most good quality monitors now have a colour gamut only a fraction smaller than Adobe RGB so you can see what you are working with and it isn’t a big enough colour space to have some of the drawbacks of the bigger colour spaces.
It’s still a good default profile for many photographers and pre-press users. It’s a popular colour space with photo libraries and if you are sending an image to be printed in a magazine or other publication it can be a good choice, but always check with whoever you are sending it to which colour space they prefer.
Adobe RGB offers more colours with few potential pitfalls and so rightly has proved a solid choice for many Photoshop users and unless you are a photographer there is little need to use anything bigger. However, when developing Lightroom Adobe choose to go with a wider colour gamut in order to keep up with gamut of colours that digital cameras can capture.
Contrary to what you’ll read elsewhere on the net Lightroom doesn’t use ProPhoto as its working space. It uses a profile with the same colour gamut as ProPhoto but the tonal curve from sRGB. Adobe don’t offer that profile as a choice in Photoshop so ProPhoto is the closest option. ProPhoto RGB is the biggest of the three common working spaces, and should really be used only by photographers and retouchers. It has a huge colour gamut designed to encompass both the capabilities of digital cameras and inkjet printers. If you convert a raw file into ProPhoto you should loose nothing and have the potential to exploit the full colour space of your printer. However, as well as being it’s big advantage its large colour gamut is also it’s biggest drawback. Such a large colour gamut causes a couple of problems.
In any 8 bit RGB file each channel can have pixel values of between 0 and 255. In sRGB the difference between, for example, 150 and 151 in a colour channel would be small. Stretch those same 256 levels across a large colour gamut such as ProPhoto RGB and the difference between 150 and 151 would be larger. This could potentially show up as noticeable steps in gradations of colour. So if you use ProPhoto RGB you must always work in 16 bit, to make the possible increments between colour values smaller.
The best computer monitors cover about 99% of Adobe RGB, none come close to similar coverage of ProPhoto RGB. If you are editing an image in ProPhoto you could be working with colours that you can not see, in fact ProPhoto has areas outside of human vision let alone your monitor gamut.
So which is best RGB working space for a photographer?
The drawbacks of ProPhoto RGB have always made me very cautious about recommending it as the default RGB working space for a photographer, similarly the small size of sRGB made me reluctant to recommend it to a customer unless they were producing images solely for the web or had some other workflow based reason why it was best for them. If pushed I would recommend photographers use Adobe RGB as a safe middle ground. However, now that so many photographers are using wide gamut RGB working spaces in software such as Lightroom it seems that the time has come for those processing images in Photoshop to also use a wide gamut working space, but how much advantage does working in ProPhoto have over the alternatives?
Looking at colour space graphs can sometimes be misleading, just because ProPhoto is a big space doesn’t mean that your images will use all that space, or that you’ll see the benefit when you print. However, I have taken images through from raw file to print in each of the three colour spaces and seen the difference on the paper. ProPhoto can retain more colour from the original scene if colour managed carefully. You won’t see the benefit in every image, but you will in some and to me it just makes sense to retain as much colour as you can for as long as you can. Who knows what technologies tomorrows printers or monitors will use to expand colour gamuts? I can’t see why so many photographers limit themselves to the gamut of CRT monitors, a technology that was obsolete ten years ago. A great video on the benefits of ProPhoto can be seen here.
So which is best RGB working space for graphic design or prepress?
If you are a graphic designer working either in print or for web, or if you are in pre-press or print and you receive RGB images from others then stick to sRGB as your RGB working space. There is no good reason for you to change from the default. sRGB remains the best colour space for images destined for the net for the moment.