Colour in Photoshop

Colour in Photoshop.

Understanding colour inside Photoshop is riddled with confusion for the majority of users.  This is due to the perpetual misuse of certain words and terms.  Adobe themselves use incorrect terminology – which doesn’t help!

The aim of this post is to understand the attributes or properties of colour inside the Photoshop environment – “…is that right Andy?”  “Yeh, it is!”

So, the first colour attribute we’re going to look at is HUE:

ColWheel1 1 Colour in Photoshop

A colour wheel showing point-sampled HUES (colours) at 30 degree increments.

HUE can be construed as meaning ‘colour’ – or color for the benefit of our American friends “come on guys, learn to spell – you’ve had long enough!”

The colour wheel begins at 0 degrees with pure Red (255,0,0 in 8bit RGB terms), and moves clockwise through all the HUES/colours to end up back at pure Red – simple!

Hue1 Colour in Photoshop

Above, we can see samples of primary red and secondary yellow together with their respective HUE degree values which are Red 0 degrees and Yellow 60 degrees.  You can also see that the colour channel values for Red are 255,0,0 and Yellow 255,255,0.  This shows that Yellow is a mix of Red light and Green light in equal proportions.

I told you it was easy!

Inside Photoshop the colour wheel starts and ends at 180 degrees CYAN, and is flattened out into a horizontal bar as in the Hue/Saturation adjustment:

ColWheel2 Colour in Photoshop

Overall, there is no ambiguity over the meaning or terminology HUE; it is what it is, and it is usually taken as meaning ‘what colour’ something is.

The same can be said for the next attribute of colour – SATURATION.

Or can it?

How do we define saturation?

Sat1 Colour in Photoshop

Two different SATURATION values (100% & 50%) of the same HUE.

Above we can see two different saturation values for the same HUE (0 degrees Hue, 100% and 50% Saturation). I suppose the burning question is, do we have two different ‘colours’?

As photographers we mainly work with additive colour; that is we add Red, Green and Blue coloured light to black in order to attain white.  But in the world of painting for instance, subtractive colour is used; pigments are overlaid on white (thus subtracting white) to make black.  Printing uses the same model – CMY+K inks overlaid on ‘white’ paper …..mmm see here

If we take a particular ‘colour’ of paint and we mix it with BLACK we have a different SHADE of the same colour.  If we instead add WHITE we end up with what’s called a TINT of the same colour; and if add grey to the original paint we arrive at a different TONE of the same colour.

Let’s look at that 50% saturated Red again:

Sat2 Colour in Photoshop

Hue Red 0 degrees with 50% saturation.

We’ve basically added 128 Green and 128 Blue to 255 Red. Have we kept the same HUE – yes we have.

Is it the same colour? Be honest – you don’t know do you!

The answer is NO – they are two different ‘colours’, and the hexadecimal codes prove it – those are the hash-tag values ff0000 and ff8080.  But in our world of additive colour we should only think of the word ‘colour’ as a generalisation because it is somewhat ambiguous and imprecise.

But we can quantify the SATURATION of a HUE – so we’re all good up to this point!

So we beaver away in Photoshop in the additive RGB colour mode, but what you might not realise is that we are working in a colour model within that mode, and quite frankly this is where the whole chebang turns to pooh for a lot of folk.

There are basically two colour models for dare I use the word ‘normal’, photography work; HSB (also known as HSV) and HSL, and both are cylindrical co-ordinate colour models:

HSBHSL Colour in Photoshop

HSB (HSV) and HSL colour models for additive RGB.

Without knowing one single thing about either, you can tell they are different just by looking at them.

All Photoshop default colour picker referencing is HSB – that is Hue, Saturation & Brightness; with equivalent RGB, Lab, CMYK  hexadecimal values:

col3 Colour in Photoshop

But in the Hue/Sat adjustment for example, we see the adjustments are HSL:

ColWheel2 Colour in Photoshop

The HSL model references colour in terms of Hue, Saturation & Lightness – not flaming LUMINOSITY as so many people wrongly think!

And it’s that word luminosity that’s the single largest purveyor of confusion and misunderstanding – luminosity masking, luminosity blending mode are both terms that I and oh so many others use – and we’re all wrong.

I have an excuse – I know everything, but I have to use the wrong terminology otherwise no one else knows what I’m talking about!!!!!!!!!  Plausible story and I’m sticking to it your honour………

Anyway, within Photoshop, HSB is used to select colours, and HSL is used to change them.

The reason for this is somewhat obvious when you take a close look at the two models again:

HSBHSL Colour in Photoshop

HSB (HSV) and HSL colour models for additive RGB. (V stands for Value = B in HSB).

In the HSB model look where the “whiteness” information is; it’s radial, and bound up in the ‘S’ saturation co-ordinate.  But the “blackness” information is vertical, on the ‘B’ brightness co-ordinate.  This great when we want to pick/select/reference a colour.

But surely it would be more beneficial for the “whiteness” and “blackness” information to be attached to the axis or dimension, especially when we need to increase or decrease that “white” or “black” co-ordinate value in processing.

So within the two models the ‘H’ hue co-ordinates are pretty much the same, but the ‘S’ saturation co-ordinates are different.

So this leaves us with that most perennial of questions – what is the difference between Brightness and Lightness?

Firstly, there is a massive visual difference between the Brightness and Lightness  information contained within an image as you will see now:

BHSB Colour in Photoshop

The ‘Brightness’ channel of HSB.

LHSL Colour in Photoshop

The ‘L’ channel of HSL

Straight off the bat you can see that there is far more “whites detail” information contained in the ‘L’ lightness map of the image than in the brightness map.  Couple that with the fact that Lightness controls both black and white values for every pixel in your image – and you should now be able to comprehend the difference between Lightness and Brightness, and so be better at understanding colour inside Photoshop.

We’ll always use the highly bastardised terms like luminosity, luminance etc – but please be aware that you may be using them to describe something to which they DO NOT APPLY.

Luminosity is a measure of the magnitude of a light source – typically stars; but could loosely be applied to the lumens output power of any light source.  Luminance is a measure of the reflected light from a subject being illuminated by a light source; and varies with distance from said light source – a la the inverse square law etc.

Either way, neither of them have got anything to do with the pixel values of an image inside Photoshop!

But LIGHTNESS certainly does.