In the histogram display I am implementing, I managed to successfully display RGB histogram. When compared with Photoshop's, it seems right-on!
(All screenshots below are from same image)
Now, for Luminosity histogram, I used the following formula:
Y = 0.2126 R + 0.7152 G + 0.0722 B
(as discussed here)
However, mine seems to be off from Photoshop's Luminosity Histogram (also from other applications'):
In fact, my Luminosity Histogram (calculated from above formula), seems to be equal to Photoshop's RGB Histogram:
Issue
What could be the proper formula to implement the proper Luminosity Histogram from RGB values?
P.S. : I've tried following formulas, but they don't seem to get me close to Photoshop's actual Luminosity Histogram:
Y = 0.2126 R + 0.7152 G + 0.0722 B
Y = 0.299 R + 0.587 G + 0.114 B
Y = 0.33 R + 0.5 G + 0.16 B
Y = 0.375 R + 0.5 G + 0.125 B
(Please note: I do understand, due to color space differences, actual formulas used by different applications, etc., histograms tend to differ slightly from one application to another. I used Photoshop as a common example. I also did compare with other image editing softwares, and the differences seemed the same.)
