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RGB – Which ‘working’ space for me?
By David Crowther

Photoshop RGB working space. What is the right space? What should you choose? sRGB, Adobe RGB (1998), ColorMatch RGB or ProPhoto RGB? How can it affect the photographer, designer, fine art reproducer and digital artist? Indeed, you may well have asked, “Is it really important?”

The phrase “working space” was invented by Adobe to describe a type of colour space that is primarily used for image editing. Working space is utilised broadly throughout Photoshop, but initially, attention should be paid to the configuration of the colour settings, where the RGB, CMYK and Greyscale working spaces are set as application preferences.

 ipf5000 adobe rgb 1998 comparison1.gif
3D comparison of Adobe 1998 RGB (shown in transparent green) with a Canon iPF5000 profile. Note how the Adobe 1998 RGB profile almost encompasses the Canon profile completely, from this angle

Many industry professionals I speak to are usually a little confused as to the actual role of working spaces, especially RGB. Whilst CMYK and Greyscale working spaces are intended primarily for output (printing or previewing on your monitor), RGB working spaces provided by Photoshop are an artificial, man-made build of numbers. “But, hang on you might say, are not the selections available for the RGB working space in the main ICC profiles? Aren’t ICC profiles are device dependent?” The answer to these two questions is a resounding yes and yes. Therefore, these RGB working spaces are based on both some sort of input (i.e. digital camera or scanner) or output (i.e. monitor or RGB printer).

However, some of the more familiar spaces such as sRGB, Adobe RGB (1998), ColorMatch RGB and ProPhoto RGB are not based on any particular RGB input or output device. Some may be based on the behaviour of a certain device under fixed conditions. Due to the methodology of a concise mathematical build these RGB spaces are fixed. They will not drift or move over time. In contrast, your output or input device will change, drift and/or move over time. What I mean by this is that through continued use, various parts in your inkjet printer will suffer wear and tear, which can translate to the quality of colour being affected.

 list of rgb icc profiles available to photoshop as the rgb working space note that some of these are monitor and printer profiles.gif
List of RGB ICC profiles available to PhotoShop as the RGB Working Space. Note that some of these are monitor and printer profiles

These artificial, man-made RGB working spaces are indeed very valuable then, not only for editing, but also for establishing a standard environment and for image archiving with the embedded working space, to allow for future output or conversion to another colour space. Additionally, they provide another distinct advantage for editing. When the RGB numbers are equal in value - R120 G120 B120 - the numbers should always render a neutral hue. This translates to a big plus in RGB workflows in that you can edit and work numerically to achieve ideal grey balance.



comparison 2.gif
3D comparison of Adobe 1998 RGB (shown in transparent green) with a Canon iPF5000 profile. Note how some the more saturated blues and reds of the Canon iPF5000 clearly extend beyond Adobe 1998 RGB.

What is the right space? Importantly, you need to know that the gamut of these artificial man-made RGB working spaces can dramatically vary in size. Space prevents me from going into the finer details of all the RGB standard editing spaces, but suffice to say just as Photoshop has changed over the years, so has the number and type of working spaces Adobe has included with the standard install. There are many RGB working spaces available today from experts and colour counsellors over the Internet. I am loath to recommend which is the right space for you, as it really is a matter of choice or horses for courses. What may be perfect for the photographer may not suit the designer and creative. In reality, there is no RGB working space that will provide absolute perfection for all.

However, there are some important points to consider when dealing with the decision of “which working space?” Ideally, your RGB working space should be large enough to contain all the colours of your digital capture device and also large enough for ALL the output devices you intend on using. Here, I am talking about colour gamut’s. The colour gamut describes the range of colours that a particular device is able to reproduce. This usually has the most meaning for us when we start talking about inkjet printers and monitors or displays.

ipf5000 adobe rgb 1998 comparison3.gif
3D comparison of Adobe 1998 RGB (shown in transparent green) with a Canon iPF5000 profile. Once again, note how some the more saturated warmer colours Canon iPF5000 clearly extend beyond Adobe 1998 RGB. Is this a profile mismatch problem?

Should you choose a working space with the largest possible gamut? Well, not necessarily, as there are a couple of issues at play here. If your RGB working space has a larger gamut than the gamut of your monitor, and the image you are working on contains most or all of the colours in the working space, some colours will be outside of the monitor’s capabilities. A smaller working space like sRGB starts to make more sense within the aforementioned scenario. Editing colours to increase saturation, for example could become unnerving if they were outside of the gamut of the monitor. In other words, the increases in saturation being made are happening but you don’t see it on the monitor. But on your inkjet print, you may! There are other considerations, such as selecting 8 or 16 bits per colour. This affects editing, together with your choice of RGB working space. Images that are sometimes called “high key”- containing only lighter tones or pastel type colours - have no need of a large working space. But images that you wish to reproduce that contain deep tones, subtle shadow detail and highly saturated colours can possibly benefit from a larger working space. Many photographers that I speak with swear by Adobe RGB 1998 and would never consider anything else. Indeed many see no reason to consider other options. They claim it is the “standard” working space. Once again I should best clarify that statement by mentioning that many photographers are using Adobe RGB 1998 as the RGB space after conversion from RAW.

This discussion could easily fill chapters in a book and it may seem that I have glossed over much of the detail. Instead I am encouraging you, as image professionals, to become aware of the fundamental questions and issues concerning RGB working spaces. Now that you have a grasp of the importance of choice in RGB working spaces, in one of the upcoming issues of Digital Reproduction, I will examine in more detail some of the standard RGB working spaces and what happens to the differing colour gamut’s when outputting to inkjet as a photographic or fine art print.