Missing automatic color/exposure correction functions (auto levels, auto contrast, auto white balance) in batch operations

[Joergi121]

Description:
I am using GIMP 3.2 on Windows 11 together with the Batcher plugin. While Batcher provides a range of color and image adjustment operations, it appears to lack support for automatic, per-image corrections such as “Auto Levels” and “Auto Contrast”.

These automatic functions are available in GIMP itself and are essential for workflows where each image requires a different adjustment based on its histogram. However, in Batcher, only fixed-value adjustments (e.g., brightness/contrast with manual parameters) are available.

Steps to reproduce:

1. Open Batcher in GIMP 3.2
2. Add a folder with multiple images
3. Try to add an operation that performs automatic color or exposure correction (equivalent to GIMP’s “Auto Levels”, “Auto Contrast” or "Auto White Balance")

Expected behavior:
Batcher should provide options to apply GIMP’s automatic correction functions (such as Auto Levels, Auto Contrast and Auto White Balance) to each image individually, using image-specific analysis.

Actual behavior:
No such automatic correction options are available. Only manual adjustments with fixed parameters can be applied.

Impact:
This significantly limits batch processing workflows, especially when working with large sets of images that require individual exposure or contrast correction. Users are forced to either process images manually or rely on external scripting instead of using Batcher.

Suggested improvement:
Please consider adding support for the following GIMP procedures:

• gimp:levels-stretch (Auto Levels)
• gimp:drawable-auto-contrast (Auto Contrast)
• gimp:drawable-white-balance (Auto Whitebalance)

Ideally, these should be available as standard operations within Batcher, similar to other color adjustment tools.

Environment:

• Batcher version: 1.2.2
• GIMP version: 3.2
• OS: Windows 11, installer from gimp.org

Thank you for your work on this plugin!

[kamilburda]

Hi, thanks for the suggestions. I guess I'll just copy all the Auto functions in GIMP for convenience and put them under a separate submenu under the Color menu.

White Balance is already available under Color. If by Auto Contrast you mean Stretch Contrast, you can, for now, add the Stretch Contrast or the Stretch Contrast HSV custom action.

Auto Levels will be tricky to implement, though, as GIMP does not offer any procedures for that.

[Joergi121]

If by Auto Contrast you mean Stretch Contrast, you can, for now, add the Stretch Contrast or the Stretch Contrast HSV custom action.

Yes, that is what I mean. I wasn't aware that this function already was available.

Auto Levels will be tricky to implement, though, as GIMP does not offer any procedures for that.

According to the docs there should be a procedure for that: https://developer.gimp.org/api/3.0/libgimp/method.Drawable.levels_stretch.html

[kamilburda]

I'll still add the Stretch Contrast functions as actions to make them more discoverable (since they are named differently).

As for gimp_drawable_levels_stretch, this appears to be the same function as White Balance (the drawable_levels_stretch_cmd_callback function internally calls gimp_drawable_levels_stretch), which is already available in Batcher under Color -> White Balance.

[Joergi121]

The three functions I use regularly are

• Auto Levels
• Auto Contrast
• Auto White Balance

For the positioning in the Batcher UI, having these three next to each other would be logical for me.

As far as internal GIMP functions go, I am not enough of a programmer to judge. The three functions I use, while they partly work on the same aspects of a given image, are however not doing the same thing. They all three are different in what they achieve.

[kamilburda]

If by Auto Levels you mean Color -> Levels -> Auto Input Levels, then that's the tricky part as that is not available in the GIMP API. However, you can always go to Color -> Levels in GIMP, press Auto Input Levels, save the preset, and then add Color -> Levels in Batcher and provide the saved preset.