How to create the equivalent of an Adjustment Layer in an editor that does not support it?

Question

As a user of GIMP I tried to understand what Photoshop's Adjustment Layers are, without actually using PS. My understanding is that GIMP does not yet support AL (is this correct?).

So, trying to imitate the effect of an AL, is it equivalent to:

1. Duplicate the image to a second layer.
2. Apply the desired effect (filter/adjustment/whatever) to the new layer.
3. Add a layer mask to the 2nd layer and set its transparency areas the same way you'd do with AL, this blending the adjusted image with the original image in the desired areas/amounts.

Am I thinking right?

I realize that there is one limitation to that method - changes to the original image layer will not affect the top layer (AL equivalent). Is there a way to lock the two images in the two layers?

Answer 1

In short, no. What you're doing is not really related. Layer masks are basically ways of working with the alpha channel of a layer. Adjustment layers aren't really layers at all — they're ways of thinking of filters within the same metaphor. They don't actually accomplish anything you couldn't do simply by applying the filters in the traditional way. However, because the layers model is very powerful, they are a convenient and powerful tool which makes visual experimentation easier.

The problem is that "apply the desired effect" is a destructive operation for the layer you apply it to — if you want to change the parameters of that effect, you have to do something to reverse it. Generally, that means recreating the whole layer. Layer masks let you choose how "strongly" to apply an effect, and limit it to certain parts of the image, but they don't change that basic limitation.

In terms of final results, there's nothing you can do with adjustment layers that you can't do just by deleting and recreating the layer every time. The problem is that if you're trying to work with the combination of multiple different adjustments (for example, blur and curves), it becomes tedious.

So, it's basically an ease-of-workflow thing, and since you can combine multiple layers, for complicated operations it can be exponentially easier — nothing to sneeze at.

On the plus side, the Gimp development roadmap has something called "Filter layers (brightness/contrast, blur, etc)" as relatively high priority. Currently, that's slated for Gimp 3.2. That's not the impending future, but it sounds like we'll get it eventually.

Answer 2

This has been asked and answered three years ago, but I'd like to refine the difference between the two types of layers.

The normal layers in Photoshop are like you said "image layers", personally I prefer calling them "raster layers".

The adjustment layers in Photoshop are data layers. They hold no function other than to overlay certain changes to whatever exists below them.
As such, they hold only the parameters for the change. Not the input, not the output. They have no existence in the world of raster.

Adjustment layers can carry an alpha with them just like any sort of layer in Photoshop can (vector, text layers).

Your suggestion for a workaround is basically an example on how to do non-destructive raster image editing.
It doesn't imitate adjustment layers because they're about the process. Adjustment layers simply aren't "just" non-destructive editing.
Since they're only data- they weigh nothing, they can be applied and reapplied on anything and everywhere, and are susceptible to changes.

Answer 3

There's nothing in GIMP that can achieve what layer adjutement can do, with LA you apply your adjustments separately so you don't have to undo the changes you make, you can also apply the same adjustement to a lot of images without repeating the same steps over and over. As the gimp developpers don't seem to add such a feat, you can try Krita, it's a painting open source software, it supports non destructive adjustement, it's called "filter layer".

Answer 4

I was wondering if you were trying to do the same thing as I do in Photoshop, which is select part of a image, create a new layer from that selection with control j and then apply things like curves etc, only to that layer without affecting the layer below. If so, this is what I do in gimp.

1) Select part of the image and do an edit -> copy

2) Create a new transparent layer, select the new layer and do edit -> 'paste into'

3) Do an anchor layer.

Now you can make changes only to that layer containing the selection without affecting the layer below. To turn the changes on and off, simply turn the new layer on and off.

Hope this helps,

Chris.