Autorange and histogram/curve display

[tomczak]

I'm probably doing something wrong, but the histogram display doesn't seem to get updated when the Dynamic Range control is adjusted.

Also, I imagine that the histogram type in Autorange simply follows the histogram/curve set in preferences Default Curve Options and can't be switched in the transformation window?

[jsachs]

Autorange always displays the input image histogram -- the controls are locked and the curve is not editable -- it just displays the curve Autorange is applying. The dynamic range is applied after the white and black points are identified so you can place them wherever you want on the tone scale.

There is a way to see the output image histogram as well as the input image histogram. Click the Histogram tool button at the top of the main window to activate Histogram mode. This will display a histogram of the current image, or the output image of the currently open transformation dialog box. This histogram does reflect changes to the dynamic range in Autorange.

[tomczak]

Cheers! But should the Autorange display the curve that it's applying to the input histogram? Please take a look at the screenshot - I'm having a hard time to move this curve.

[tomczak]

This is interesting: if I change the Default Curve Options in Preferences to dual histogram and restart the Autorange, it shows input and output histograms properly (I think) but, just like the curve previously, is unreactive to changes to the Dynamic Range slider.

[jsachs]

I fixed it for the next release so the default curve options are not applied in Autorange.

[tomczak]

The Autorange displays Curves version of the histogram now, regardless of Settings. But while I understand that it shows the input histogram only and the controls are disabled, the actual mapping Curve seems to still behave strangely:

- Curve stays diagonal regardless of Dynamic Range slider adjustments
- The Curve does react to an initial adjustment of Thresholds, but also not quite right to my eye, and gets stuck from there on
- Resetting the transformation returns the curve to diagonal

I can attach screenshots if this can't be replicated.

[jsachs]

OK, I fixed the Autorange curve for the next release so it responds to changes in the dynamic range slider, although this does not add any useful information.

Changing thresholds is, as far as I can tell, working OK. This may or may not have much effect, depending on the image.

The way autorange works is to scan the input image histogram from each end, advancing until the sum of the histogram bars exceeds the threshold times the sum of all the histogram bars. This trims off a small percentage of the highlights and shadows to find the white and black points. If you just search for the lightest and darkest pixels, a single stuck pixel, dust speck or tiny specular reflection can set the white or black point in an undesired way.

The main purpose of the curve is to show you what parts of the histogram are being cut off.

[tomczak]

Cheers! And sorry for being a wet blanket...