01-29-2024, 06:07 PM
Unfortunately, the documentation I've been able to find says little to nothing about what is actually being done to the image when the "Auto Input Levels" button is selected on the "Color>Levels" tool. The GIMP User Manual section says only "Auto: Performs an automatic setting of the levels." which is applied to All Channels.
This question arises as a result of what I'd call quite remarkable results that are produced by the Auto Input Levels when NOT being able to come even close to getting the same results by using the other available (e.g. manual) options for making adjustments.
The related image files were produced by scanning some pretty old film strips (35mm negatives). For example, when the scanner produced image file is opened in GIMP and a jpg image is created before making any edits the result is as follows:
![[Image: Neg101.Original.jpg]](http://gowdygroup.org/photos/Film-Roll03/Neg101.Original.jpg)
Then when doing nothing other than applying "Color>Levels>Auto Input Levels" the similar jpg image file that results follows:
![[Image: Neg101.AutoLevel.jpg]](http://gowdygroup.org/photos/Film-Roll03/Neg101.AutoLevel.jpg)
To the extent that it might matter a screenshot of the tool ("Adjust Color Levels") values associated with the original image file shown above is as follows:
![[Image: AdjustColorLevelsWindow.jpg]](http://gowdygroup.org/photos/Film-Roll03/AdjustColorLevelsWindow.jpg)
Note: When the "Auto Input Levels" button is selected the image is changed quite dramatically in this case but nothing gets changed/updated within the "Adjust Color Levels" window.
These examples are derived from using GIMP 2.20.36 on Windows.
My thinking is that "Auto" means the tool is doing the same things described in the documentation that I should be able to do manually. One might even think that the window which shows changes when made manually could be updated to reveal what changes that are being made automatically. Of course this is NOT possible if "Auto Input Levels" is doing something different than what a user can do on there own. If so, it would be nice to at least know what kind of things are possible when selecting "Auto Input Levels" that cannot be done otherwise.
This question arises as a result of what I'd call quite remarkable results that are produced by the Auto Input Levels when NOT being able to come even close to getting the same results by using the other available (e.g. manual) options for making adjustments.
The related image files were produced by scanning some pretty old film strips (35mm negatives). For example, when the scanner produced image file is opened in GIMP and a jpg image is created before making any edits the result is as follows:
Then when doing nothing other than applying "Color>Levels>Auto Input Levels" the similar jpg image file that results follows:
To the extent that it might matter a screenshot of the tool ("Adjust Color Levels") values associated with the original image file shown above is as follows:
Note: When the "Auto Input Levels" button is selected the image is changed quite dramatically in this case but nothing gets changed/updated within the "Adjust Color Levels" window.
These examples are derived from using GIMP 2.20.36 on Windows.
My thinking is that "Auto" means the tool is doing the same things described in the documentation that I should be able to do manually. One might even think that the window which shows changes when made manually could be updated to reveal what changes that are being made automatically. Of course this is NOT possible if "Auto Input Levels" is doing something different than what a user can do on there own. If so, it would be nice to at least know what kind of things are possible when selecting "Auto Input Levels" that cannot be done otherwise.