Colour modes vs colour spaces
Sometimes in my group I see this question: "I thought I was working in sRGB, but it says RGB!"
This confusion can be caused in a few places, most commonly in the title bar at the top of the window in Photoshop:
At the heart of this question is a common and lamentable problem – people refer to Adobe RGB as simply "RGB". This is bad. Adobe RGB is a type of RGB. RGB is a colour mode, whereas Adobe RGB is a colour space. Let me explain with an analogy …
When I’m out driving, I see several modes of transport – eg cars, buses, motorcycles and trucks. Each of those transport modes have their own purposes, their own benefits, and their own drawbacks. Within those modes are various types – if you drive a car you could choose a Toyota, a BMW, a Hyundai, a Porsche, etc, etc. If a motorcycle is your preferred mode, you could choose a Ducati, a Honda, etc. And so on.
In colour, RGB is a mode. All cameras capture red, green and blue light – therefore, all cameras capture RGB mode. Other modes are CMYK, L*a*b*, Grayscale, etc. (RGB is by far the most commonly-used mode – the others are only for specific purposes, and shouldn’t be used without good reason and understanding to do so.)
Within RGB mode, you get to choose your space. The most common RGB colour space is sRGB, followed by Adobe RGB and ProPhoto RGB. (I’ve written more comprehensive information colour spaces here.) Colour spaces can also be referred to as "colour profiles".
So, if you see "RGB" at the top of your image window, it’s talking about the mode. Of course, you’ll notice that it changes all the time – if you’re using an adjustment layer, it won’t say "RGB/8", it will say "Layer Mask/8". (By the way, the "8" refers to bit depth, which I’ve written about here.)
If you want to see what space your image is in, follow the directions in the first tip on this page.
If you have a question about this article, please feel free to post it in Ask Damien.