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I've recently been having a discussion and some thoughts on Hue Histograms and how it may help us in processing an image.  Things did not turn out as I thought they would - basically because it is pretty meaningless (I think!) to inspect Hue without taking into account the Saturation & Brilliance channels, as this snapshots shows of a couple of Hue clocks for 67 degrees (the histogram scale is all at 100%).

I then wondered, if the 5 stop tonal framework comparison (I did of the landscapes) could be meaningfully expanded to colour.  This turned out to quite an interesting exercise using the HSB colour space. 

I chose a recent outdoor scene that I had taken and enhanced to do the comparison.  I did not do this while I was processing, but it may have been a good idea.

I have chosen to de-saturate the "5 Stop Tones" action (into grey bands, rather than blue etc.) as the colouring may confuse the picture!  Remember that in the 5 band split, all detail is lost and we just have bands of grey shading.

To the right of the pair of images below is the difference between them (Black means no difference and White more difference - slightly exaggerated by a Levels adjustment layer - same setting for all of them).  Again except for the first one, they are just 5 bands of grey.

[Just to recap - the "5 stop tones" action splits the image up into shadows, 3/4 tones, mid tones, 1/4 tones and highlights and assigns a colour to each band]

the full image - may be obvious which is before!

5 stop Tones (L channel) - notice the increase in detail in the sky, building and grass at the cost of the left tree

Brightness channel of HSB - so this shows that some of the colours have darkened

Saturation channel of HSB - the main change is the blue sky saturation (and the trees, L&R),
but overall the colours have been blown apart a bit (steeper A&B channels).
Note that the stripes on the lawn are more pronounced in this channel change - band boundary?

Hue channel of HSB - really showing virtually no change

So it was the Luminosity and Saturation channels that were mostly changed during the post-processing.  If I remember correctly all the processing was done in a single pass of Lab using CurveMeister.

I am reasonably happy with breaking the channels up into 5 bands, except for the Hue channel where this represents 70 degrees which is rather large to show the split of basic colours.  From my exploring the subject of colour perception, I'm convinced that we can differentiate the 0-120 degree Hues much better than the rest and that the Munsell classification seems to bear this out.  Therefore if looking at bands of colour is to be taken seriously we need at least 6 (unequal) bands.  However splitting colours up using Munsell is not easy (as I found out when I added that colour space to the Colour Watcher) and would need a program, rather than a simple PS action.

This is almost getting me re-interested in the "Learning from the Masters" project - but it is summer, so it will have to wait.

I have a feeling that if we had a dynamic 5 band view of the image as we curved, it may be useful.  This is easy to achieve and would allow one to curve to set the overall tonal (or colour) framework for the image before getting down to the detail of specific areas.  This would be an extra step, but probably well worth it for those special images - food for thought!