Does GIMP has a before/after slider function? Something like the darktable before/after slider. But I want to compare two different images and darktable has no layer function.
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I don’t use darktable, so I might be misunderstanding, but when I do something in gimp and then want to look at before/after I use Edit->Undo and Edit->Redo
Nope, that isn’t it. I created an animated GIF (online) with the images I wanted to compare.
I’m also looking for a way to compare photos this way.
There is a thankfully easy way to do what you want, though it’s not a “feature” like a before/after slider. Layers!
When you open an image in the GIMP, always start by duplicting the initial image layer (there is a button on the Layers palatte and a menu option do to this). You’ll thus add edits to this new, added layer, and the original, the bottom-most layer, can remain unchanged as you modify the new duplicate layer, or any other layers you may add. In fact, I’d leverage the GIMP’s layers to add them for each successive edits made (e.g., 2nd layer for Color mods, 3rd layer for G’MIC mods, 4th layer for Shadows/Hightlights, Brightness/Contrast, etc.). If an edit goes awry, one can either use Undo, or simply delete the layer, duplcate the layer below it, and keep editing.
The before/after part is that the GIMP allows you to toggle layers on and off with a single keystroke (rather than use the Eye symbol in the Layers palette on each added layer): SHFT-Click on the Eye symbol for the BOTTOM layer and all layers above it are “turne off” and thus, the changes made to them become invisible. This way you can toggle the original, unchanged layer into view, then SHFT-Click the Eye again to show all the changes.
I’ve been doing this for, literally, years. No need for a special function in the GIMP to do something that is so easly done already. One simply needs to remember to duplicate the first layer before starting one’s image edits.
Hope this helps.
On all GEGL filters in GIMP → check that “Split View” button while you are using a filter, on the left the effect, on the right the original before effect.
You can even move that vertical splitting dashed line to extend on one side or the other side
So " Does GIMP has a before/after slider function?"… Yes! 
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GAH! I cannot believe I didn’t think of this LOL
Should note that it works also on non-GEGL filters (e.g., Saturation, etc.) - they should all have that "Split View’ option. But it’s only available for the selected tool as it’s being used (that is, before the OK button is selected and the tool closes).
My previous comment about using SHFT-Eye on the bottom-most layer in the Layer palatte, if that layer was dulicated first, still works.
Thanks. This definitely helps, but can split view be applied to two different photos? not a photo and an applied filter inside GIMP. For example, comparing quality of an image after compressing it.
Most colors tools, and all GEGL filters (those with a G icon in the menu entry) have a “Split view” option for this:
Otherwise in case if dire need you can jury-rig one yourself if you have the before/after versions as layers:
- Add a layer mask on the top one
- Select the
FG to BG (hard edge)gradient and fill the mask with the gradient - While still in the blend tool, click in the middle of the gradient segment to grab the gradient midpoint
- Moving the midpoint will then act as moving the slider.
