Chasing the missing colours further

The mystery of the missing adobe colours turns out to be is as simple as understanding the Colour Space being used in the HSL sliders, some unfortunate naming, and confusion on my part. I have exhausted my way around bothLightroom and Photoshop documentation and on-line tutorials etc. I did find a few others asking similar questions and found a few also doing direct tests on Lightroom with colour charts (see my approach below). I still had that empty feeling I was misiing something important.

I decided to investigate the missing colours for myself, I took a series of of different colour wheels into Lightroom (below is a conventional painters colour wheel) and just played around with the Hue Sliders in the HSL panel of Lightrooms Develop Module. This can be a lot of fun and well as giving you a sound understanding of how the sliders work. I strongly recommend trying it out for your self.

What I discovered  was first that the sliders did actually cover the full Hue (colour) range. Adobe have provided 8 slidesr so they where spaced 45^o apart (ie 360^o/8). Also each slider has an adjustment  range form –100 to +100 which seemed to cover 3 or 4 segments on the standard 12 division colour wheel (shown below). There also appeared to be some overlap with the adjacent sliders.

The next bit of the analysis is just my approximation. I assumed that each slider goes half way to the next slider plus a bit (ie 45^o/2 = 22.5^o plus 10^o) Then doubling that for the full movement of the slide from minus to plus yield 64^o (32^o*2) which is inline with my observations above. Now things where coming together,  I could build the table below and work out the range of HUEs in terms of the angular HSL measure.  the –100 column if the anticlockwise Angular number (eg, –23^o) and the –100 column is the clockwise angular number (eg, +23^o), give the extent of that slider in terms of Hue.

Adobe Colour	-100	Hue	+100	Better Colour Name
Red	328o	0o	32o	Red
Orange	13o	45o	77o	Orange-Yellow
Yellow	58o	90o	122o	Yellow-Green/Chartreuse
Green	103o	135o	167o	Green
Aqua	148o	180o	212o	Cyan
Blue	193o	225o	257o	Blue
Purple	238o	270o	302o	Blue-Purple/Violet
Magenta	283o	315o	347o	Magenta

I also to a HSL Circle (colour wheel) on which our common colour names had been applied to given segments. The obvious feature is our colour names don’t forma linear arrangement around the circle. Some colours (eg Yellow) have narrow range while others (eg green have a very broad range) at least in terms of their name.

Suddenly some of my previous observations, like if I used the yellow slider it was more likely to adjust the grass and foliage than the orche coloured yellowed of bleached grass or rocks. That the reds were very sensitive to their sliders whereas blues and greens less so. I also have taken the opportunity to better name the colours of the sliders. Thus now the Orange slider (now Orange-yelloe and the yellow slider (yellow-green) might both be required to enchance of shift the Yellowness of an image. Admittedly things get a little complex when luminance is also considered, that can be a latter topic for a post, but for now a better understanding of which hues are affected is a big step in the right direction to understand how to control colour in your Photograph.

So in conclusion, rather than there being missing colours, I found the names the HSL sliders where given in lightroom had lead me to think back to a conventional colour wheel (3 primaries, 3 secondary and 6 tertiary colours, ie 12 colours). Instead I should have realized Adobe had split the 360^o of the HSL Hue Circle into 8 division rather than 12. C’est la Vie