According to the manual, the "histogram" graph plot has the X axis represents values of pixel, from 0 to 1 (or 0 to 255), while the Y axis represents the number of pixels in that tonal range.

When I draw a "sample line" on my image, I got the graph plot that looks like it has the X axis represents the pixel point/position, while Y axis represents the brightness (luma) for each points.

There is no further explanation on the graph plot of sample line in the manual.Can someone clarify whether the XY axis for "sample line" graph plot mentioned above is correct or otherwise?

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    $\begingroup$ The units of measurement for the sample plot are Luma, which is the weighted sum of gamma-compressed R′G′B′ components of a color video—the prime symbols ′ denote gamma compression., explained in detail here: en.wikipedia.org/wiki/Luma_(video) $\endgroup$ – TLousky Nov 5 '19 at 9:20
  • $\begingroup$ @TLousky Thank you! I have corrected it in my questions. Do you happened to know the answer? $\endgroup$ – NabilaM Nov 6 '19 at 6:40

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