In that article, I’ve shown where the stops levels are on both linear and RGB space histograms. This is explained in my article A Better Histogram, which includes true stops histograms. Photo histograms are histograms of RGB data, so the horizontal axis is warped by the TRC of the particular RGB space. Moreover, the claim that the horizontal axis of a histogram is a stops (logarithmic) scale is wrong. The Photomorrobay article wrong because it seems to be confusing raw data with RGB data. Long story short, the TRC transformation is why 8 bits in sRGB or ProPhoto can have as much dynamic range as 14-bit raw data. RGB space data has been transformed by the inverse of the tone reproduction curve (TRC) of the particular RGB space. sRGB, Adobe RGB, or ProPhoto RGB data is not linear. It is important to always keep in mind that the 50% in the top stop rule only applies to linearly quantized data, which means linearly proportional to the photon count at the sensor. Other than that, you are correct, that that article is pretty much off the rails. I will credit that article for using the term “discrete tonal value,” which I refer to as quantization levels, rather than “data” which, sorry, is just wrong. A search has brought up this: but there are a lot of other references around if you look.ĭave – I checked out this reference – although I didn’t read the whole thing. There was a discussion pointing out that “the top 3% contains 50% of your captured data!” was a myth.

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