Re: Logarithmic histogram
On Monday, 5 Feb 2001, Jay Cox wrote: Linear, Log, and sqrt are all common ways to scale histograms for display. Perhaps we should make it an option in preferences (or in the histogram display itself). sqrt() - I haddn't thought of that. That sounds plausibly like what Photoshop is using. I might have a play with that. Austin
Re: Logarithmic histogram
Linear, Log, and sqrt are all common ways to scale histograms for display. Perhaps we should make it an option in preferences (or in the histogram display itself). sqrt() - I haddn't thought of that. That sounds plausibly like what Photoshop is using. I might have a play with that. To me, it looks like Photoshop uses linear, but if there are some peaks that are very high relative to the rest of the histogram, they don't show these peaks completely (they are clipped off) in order to be able to show some detail in the lower parts. I tried something similar in Gimp, and for a number of images I tried, the histograms of Photoshop and the Gimp were very similar. If you want, I can post the code I used for it. I'm not sure about how to determine the clipping, though; now I have done something like (I don't have my code here with me) after the calculation of max in the function that calculates the heights of all peaks (I forgot the name) avg = ... if (max avg * 4) max = avg * 4; Note: the average is not the average as shown in the histogram widgt; it is the average height of all peaks in the histogram which is something completely different. But perhaps it is better to use the median instead of the average, or maybe the 90% percentile or something. Roel Schroeven
Re: Logarithmic histogram
Austin Donnelly wrote: On Sunday, 4 Feb 2001, Roel Schroeven wrote: I noticed in the source code that the histogram widget uses a logarithmic scaling. Is there a reason to do it that way, as Photoshop et al. seem to use a linear scaling. I just checked the CVS history; we've been using a log y axis (ie pixel count) ever since the histogram widget was writen. Jay Cox checked in the initial rev (including log scale) in March 1999. I've played around a bit with gimp looked at some web-based tutorials for histogram use in photoshop, and while I agree that gimp's log axis graphs don't look very similar to photoshop's, I don't think photoshop just uses raw counts. They also scale their data, but a little less aggressively than by a log scale. Austin Actually the log histogram was around before I ever heard of gimp. I merely converted the existing histogram display into a real widget. I expect that the log scale on histograms dates from the days of Spencer and Peter. Linear, Log, and sqrt are all common ways to scale histograms for display. Perhaps we should make it an option in preferences (or in the histogram display itself). Jay Cox [EMAIL PROTECTED]
Re: Logarithmic histogram
On Sunday, 4 Feb 2001, Roel Schroeven wrote: I noticed in the source code that the histogram widget uses a logarithmic scaling. Is there a reason to do it that way, as Photoshop et al. seem to use a linear scaling. I just checked the CVS history; we've been using a log y axis (ie pixel count) ever since the histogram widget was writen. Jay Cox checked in the initial rev (including log scale) in March 1999. I've played around a bit with gimp looked at some web-based tutorials for histogram use in photoshop, and while I agree that gimp's log axis graphs don't look very similar to photoshop's, I don't think photoshop just uses raw counts. They also scale their data, but a little less aggressively than by a log scale. Austin
Logarithmic histogram
I noticed in the source code that the histogram widget uses a logarithmic scaling. Is there a reason to do it that way, as Photoshop et al. seem to use a linear scaling. Sorry if this has been brought up before; I searched in the mailing list archives, but didn't find anything on it.
