GNOME Bugzilla – Bug 674819
Strange computation of histogram
Last modified: 2012-05-07 23:54:18 UTC
Created attachment 212816 [details] ImageLab-luminance.png First of all I would like to write about motivation of this bug report. I gave simple task to my students. They had to develop simple GUI application computing several types histogram from images. I was very suprised, when I copared histogram of Gimp with histogram computed by Gimp. All histograms of "brightness" are computed from Value (it is Value from HSV color model) in Gimp. It means that the value is computed with following formulae: Value = Max(R,G,B) You can see value channel and histogram in attachement (ImageLab-value.png). Previous computation of histograme is IMHO strange, because humane beings perceive brighteness of RGB image in different way. The relative luminance should be used for computation of histogram: Y = 0.2126*R + 0.7152*G + 0.0722*B This formulae is also used in Gimp, when image is converted from RGB to grayscale image. You can see luminance channel and its histogram in attachement (ImageLab-luma.png). You can also compare all histogram from testing application with histogram from Gimp (Gimp-histogram.png).
Created attachment 212818 [details] ImageLab-value.png
Created attachment 212820 [details] Gimp-histogram.png
Created attachment 212821 [details] Lena.png Reference image of Lena
Known issue, should be addressed in 2.10 finally. *** This bug has been marked as a duplicate of bug 109161 ***