Does anyone one know how to read the histogram values produced by Achemist
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Indexes are luminosity levels on scale 0-255
The value of each item is the number of pixels with that luminosity.
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So in the above screenshot, there are 5400 pixels with a luminosity value of 13
Is this correct @Jarda
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yes that is correct…
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Thank You @Jarda I should be able to use those values now.
Bonus question 
I didn’t notice this, but is there a way to get separate histograms for R, G and B channels?
Yes. Instead of document instance, you will ask the channel for histogram. So histogram of e.g. red channel.
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One thing you need to note here is that histogran readings can only be assumed to be fully accurate if the Cache Level is ‘1’. This can be achieved by selecting ‘Uncashed Refresh’ from the histogram menu. (Check that the stated number of pixels is equal to w x h.)
I had a situation where the histograms looked wrong and the standard deviations were around 30 for the colour channels. When I did direct calculations on the source data I got standard deviations of around 50. The histograms only looked right and only gave standard deviations of 50 when I forced Cache level 1. It took me days to uncover this. Basically higher levels of cache, means that pixels have been averaged. If the image is smoothed then no problem,but not otherwise.
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