Towards a new Colour Wheel, but Why?

For a while now I have been bending the ears of my colleagues and friends incessantly about a “digital” colour wheel with 6 primary colours rather than 3. Looking back in the blog post I  hadn’t posted anything in here (yet!) So now is the time to fix that.

	Adobe Primary & Secondary Tertiary Red Red Red Orange Orange Orange Yellow Orange Yellow Yellow Yellow Green Green Green Aqua Blue Green Blue Blue Blue Violet Purple Violet Magenta          ? Red Violet

I started to personally  question the colour wheel adopted by adobe ( within lightroom and photoshop) for their omission of some colours in their digital post processing. It only gave me 8 colours, halfway between the convention 6 primary & secondary or the 12 primary secondary & tertiary colors I expected)?

Why have they done that?

So I looked at the ways are colours are handled in the camera, computer screens and then onto printers. Well they are not even in the same colour spaces, or built using the same colour models. Cameras and Computers screens (and any direct transmission of light) follow the RGB (Red Green Blue) colour model.  This an called an additive model of how colour works, because different wave lengths of light get added together. This somewhat matches the rods in out eyes which give use colour perception. We can only discern colour because different cones in or retina can detect different wavelength. If you mix projected light of these three colours you get pure white. Ok good but should that be yellow rather than green (green is a secondary colour isn’t it?). Damn if I mix green and red light I can get yellow?

Things get even more bizarre when you start looking at printing colour.  Traditional three colour printing and many inkjet printers use a different set for their primary colours (CYM) Cyan Yellow and Magenta! This is called a Subtractive colour model because certain wavelengths are removed from the reflected image. What is going on here? When in comes to reflected light and pigments mixing colour is again different, for example to get green you mix your light blue (cyan) and yellow!! If you mix all the three colours you get a dark muddy colour, close to black but not a true black. So many primers (and ink jet manufacturers) also use a per black to create the CYMK (K for black) scheme.

Close to a year ago I was doodling in my sketch book, and realized by combining these two colour schemes I had a new colour model with 6 primary colours. Not surprising, the idea of a RGBCYM[K] colour scheme has occurred to others and is sometimes called the modern or digital colour wheel.

I know I haven’t answered the big question why Adobe and many other photoeditors only give to eight color sliders. I can’t find out why (at the moment). This is a big topic so I will build and develop over several blog post to come.

Other Blog posts in here around the mysteries of Digital Colour Theory

• Building a Digital Colour Wheel
• Just How Many Colour Models/Spaces are there?
• Getting more Colours with Bit Depth
• The Gamut of Colour Spaces
• Chasing the Missing Colours
• Colour Names and the Martian Colour Wheel
• Luminosity and Tints & Shades
• Colour should be Fun
• Colour Calibration :: Before You Panic I
• Colour Calibration :: Before You Panic II