[Not a bug] Cropping alters curves histogram

[FalCT60]

Hello,
I wonder whether this is normal behaviour or not, but after cropping a photo the histogram curve gets altered according to the crop factor.
This can be seen on the attached picture : left the original sized photo histogram, right the cropped one.
Regards,

J.-Luc

[afx]

The histogram is shown for the crop, otherwise it would be quite confusing, why should stuff that was cropped out still be shown in the histogram?

cheers
afx

[FalCT60]

Hello,

Yes, of course, the histogram shown for the crop only concerns the cropped part. That's what is expected from it.
What puzzles me is the way it is displayed : as if itself were lowres-JPEG'ed or displayed through a grid filter. But maybe is this normal.

Regards,

J.-Luc

[grubernd]

shouldnt stay around for too long. i think it's a speed optimization thing.

[claudermilk]

I don't think it's normal. I have never seen the histogram look like that in my use.

[maggus]

Hi J.-Luc,

yes, looks really strange.

Just some ideas which I could imagine lead to such a problem:
(0) on any image or just some specific ones (maybe also test with some JPG as input).
(1) what is the size of the cropped area, is it damned small ?
(2) auto-levels ON ?
(3) any processing active (e.g. NN, WaveletDenoise, ...) ?

Some time ago I was playing a bit with Photivo ... and there I could see similar (or even more strange) efefcts in the histogram depending on the filters applied to the image.

cheers
Markus

[FalCT60]

Hello,

In fact, and thanks to Maggus, I found that it is tied to both the crop size and the amount of data in the cropped area.
The histogram in my 1st post is from a crop that is ~1/6 the original photo, and the area is nearly poorly contrasted.
If I move the crop to another area of the photo that contains more details, the histogram becomes more accurate.
So this seems to be a normal behaviour : the grid the histogram displays into is of fixed size and behaves like a magnifier to display the information within.

Thanks again,

J.-Luc

[claudermilk]

Ah, well if it was a very small crop combined with a particular data set I can see how that histogram was arrived at. I would say rather a more "normal-looking" than "accurate" histogram; it sounds like both were accurate, just the one looked odd.

Yes, the control display is a fixed size and only displays the data from the current crop.

[FalCT60]

OK, so I think I can add something before the title of the topic to mean it isn't a bug.

Regards,

J.-Luc