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Peter Werner

More strange Adjustment Layer/Filter Layer blending problems

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Affinity Photo 1.3.4 (App Store build).


I was experimenting with creating a simple high pass effect:


  • Open image
  • Place an Invert adjustment on top
  • Set the blend mode of the Invert Adjustment Layer to Linear Light and Alpha to 50%.
  • As expected, everything is 50% gray.
  • At this point, lowpass filtering the top layer in any way (blurring, median etc.) should theoretically produce a high pass filter effect (it works fine when doing this with a duplicate of the base layer).


I tried to do it using only the Adjustment Layer and no duplicate of the base layer. My first attempt was the blur option in the layer styles. With or without "Preserve Alpha" on, this did not have any effect whatsoever.


I then created a Gaussian Blur filter layer and nested it inside the Invert Adjustment Layer.


With "Preserve Alpha" on, this does not have any effect either. With "Preserve Alpha" on, however, this leads to the edges of the tiles of the memory manager becoming softened (i.e. each tile's alpha gets blurred individually). The image itself is not being blurred at all. See attached Screenshot.


I'm not sure which parts of this are by design and which parts are bugs. Should applying blur to an Adjustment Layer, either as a Layer Style or as a nested filter layer, theoretically lead to the adjustment being applied to a copy of the original image, then blurred, and then blended with the original? That's what I would intuitively have expected to happen.


If not, maybe the Blur layer style should be disabled for Adjustment layers and Adjustment Layers should not allow Filter Layers to be nested inside of them, because it's kind of confusing if they have no effect.


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Hi Peter


Some interesting stuff here. Obviously I am not privy to your endgame, but this seems like quite a long process to get high pass filtering, especially when we have a dedicated high pass filter!


The nested blur filter only affect the layer it is nested in, which in this case is a n alpha layer. So effectively you are blurring a transparent layer, to which I would not expect to see any difference. This is also who checking protect alpha does not show any changes. 


This is also why it works on a copy of the layer with the image on it, as there is more that just alpha information to manipulate.


So I agree with your final point here that perhaps we should prevent applying filter layers to adjustment layers. Also the iled blurring does look quite bad so i shall look into theee

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Hi Chris,


thanks for your reply!


Building my own high pass filter was more or less just an experiment. Doing stuff like this manually allows me to freely choose the type of low pass filter being used. For instance, it would be entirely possible to use a median filter, motion blur, noise reduction, or even some kind of smudge brush to extract detail instead of the default Gaussian Blur that the built-in high-pass filter uses. A median filter will not generate glow artifacts around the edges for example when used for sharpening. But I digress.


The thing I'm not quite sure about is what the result of applying effects to adjustment layers is supposed to be. If I understand you correctly, it would be that nothing happens. That's a bit counter-intuitive for me.


With respect to blending, an adjustment layer generally behaves like a merged copy of the layers below that the adjustment is then applied to, and in the final step, the result is composited on top of the original image.


So when a blur layer style is applied or when a filter layer is nested into the adjustment layer, the question is then in which order the effects are being applied and if it should be that way. If the current behaviour is by design, that means the effects just see the Adjustment layer as being completely empty with solid alpha and as a consequence have pretty much no effect (the tile bug aside of course). What I had expected was that they would see the adjustment layer as an adjusted version of the composite below, so that if I, say, wanted to multiply a desaturated and blurred copy of an image onto itself, I'd just throw on a black and white adjustment layer with a blur applied and set it to multiply.


I'd say that would be a much more useful and logical behaviour than just doing nothing or disabling effects for adjustment layers altogether since it allows for a few more things to be done completely non-destructively without any copies of base layers.


By the way, another strange thing I came across is that nesting an "Add Noise" filter layer inside of a fill layer generated via "Layer > New Fill Layer" will not have any effect, whereas it does work fine with a regular Raster or Curve layer.

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