What happened to histograms?

[ajax]

My GIMP 2.10 (as well as 2.10.2) on Windows 7 (64bit) does NOT display any histograms on the "Adjust Color Curves".  Did I do something wrong?  Maybe some obscure setting that I can't find?  I think this is important.  Hard to imagine it could go unnoticed.  What's going on here?

[Ofnuts]

Still there for me...



Maybe a problem with the theme colors?

[ajax]

Well now!  It looks like you are correct.  See attachments.  My aging eyeballs just couldn't see it.  I failed to consider that the linear histogram might, essentially, disappear.  When changing to logarithmic it appears.

Is it possible that you know what conditions might make the linear histogram useful?  Also, while we're at it, might you be able to explain why the histogram shown by GIMP is so different from Rawtherapee.  The attached histograms are all for the same image file.

[Ofnuts]

The problem with the linear histogram if that the most frequent value is 1. If you have a white background, 50% of your pixels are white. The other 255 values are usually at best at 2%, so hardly visible (1/50th of the total height). For the difference with RT, one explanation could be that Gimp is showing you the gamma-corrected histogram (the other pair of icons, next to linear/log).

[ajax]

OfnutsThe problem with the linear histogram if that the most frequent value is 1. If you have a white background, 50% of your pixels are white. The other 255 values are usually at best at 2%, so hardly visible (1/50th of the total height). For the difference with RT, one explanation could be that Gimp is showing you the gamma-corrected histogram (the other pair of icons, next to linear/log).

It is true that RT does not offer a choice between linear & logarithmic.  It seems like it might be one or the other if not something else.  This caused me to undertake some more experiments which lead to another finding that might be worthy of some explanation.  As it turns out both GIMP and RT do allow for display of Red, Blue, and Green channels separately.  When I do that the histograms for both the Red and Green look quite similar for both GIMP and RT.  However, the Blue channel could not be much more different.  Furthermore the GIMP Blue channel looks pretty much like the situation that provoked the post where I basically just didn't see anything.

Following are 3 images that show side by side comparisons the Red, Blue and Green histograms for both GIMP and RT made from the same image as referenced previously.  It looks to me like something is amiss.  What do you think?

   

   

   

[Ofnuts]

You would have to ask the RT devs. Maybe RT doesn't use the maximum count to size the histogram (butfor instance uses median or average).

[ajax]

(05-31-2018, 05:56 AM)Ofnuts Wrote: You would have to ask the RT devs. Maybe RT doesn't use the maximum count to size the histogram (butfor instance uses median or average).

It may be a good idea to pose the question to RT.  However, I'd expect them to pose the same question I am.  Why is GIMP's Blue Histogram so different from the Red and Green when that is not the case for RT?

[Kevin]

I'd suggest posting this question on https://discuss.pixls.us/ where you'll get RT expert opinions (and maybe responses from darktable and PhotoFlow developers to add to the mix)

[Ofnuts]

Also if you post the image from which you get the histogram, you can get better answers than just guesses.