I am trying to understand the histogram for that picture.
The x-scale is the luminosity (?) with the dotted line in the middle corresponding to the grey part around the picture. There is a peak there in the histogram which more-or- less correponds to the pavement. However, the jacket of the gentleman is quite dark, and I would expect another (smaller) peak at low values, that I do not see? What am I missing?
I would recommend you start using the waveform. It is a far superior way to analyse your image as the data tracks with the image and is not simply a binned account of the pixel values
So, the spike in the middle of your screenshot histogram are the darker regions of the photograph, but I don’t know how ART is doing the binning to get the low flat line on the left-hand side…
The histogram visualization has different options for plotting the axes in log scales, so whereas I guess what you are showing is in linear X scale?
Anyway, by clicking on the bottom left icon next to the histogram (the one with vertical stripes) art (and RT) will show a pointer to where in the histogram you are while moving around the picture with your cursor.
In log mode, there was a bug in displaying the indicator lines corresponding to the pixel under the cursor. That should be fixed now, thanks for the report!