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Peter Werner

Blend Modes on Filter layers not working as expected

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Here is how to reproduce:

  • Create some black text
  • Put a Gaussian Blur layer on top
  • Set its blend mode to Multiply

You would expect a blurred copy of the composite underneath to be multiplied with the non-blurred composite. Instead, it seems to simply blur the composite below and completely ignores the blend mode – in fact, it does not do any blending at all (except if you change opacity, in which case it interpolates between the filtered copy and the unfiltered original underneath, also interpolating the alpha of the two images).

 

As a default behaviour this is fine – you wouldn't expect the layer to be blended with anything below, you would just expect it to replace everything. However, once the blend mode is changed, you would expect blending to happen. 

 

In fact, the current standard behaviour for filter layers should be called something like "Replace" (could actually be useful for regular layers as well as something you might set your layer to temporarily if you want it to replace everything below, as it has an effect similar to the Option+Click isolation mode). Once you would change to Normal or something else, it should do blending like regular layers do. The current Opacity slider behaviour would also work really well for this "Replace" blend mode.

 

I realize this is half bug report half feature request, but you intend to not implement that kind of functionality, the blend mode drop down and advanced blending options button should at least simply be disabled for filter layers.

 

Also worth contemplating is whether any document background colour should be considered by filter layers or not – i.e. if the final composite should then be composited on top of that background colour or if that background should behave like a layer on the bottom of the stack like it does now. I'm inclined to favour the former unless the bottom-most layer has a blend setting other than Normal applied.

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Hi Peter

 

Your post has me a little confused so you'll have to excuse me somewhat as I'm not sure exactly what the exact issue is here.

 

From the 3 steps you give at the top, you are using the multiply blend mode over black text. This will not provide much difference is the look as Multiply is a 'darkening' blend and black is pretty much as dark as it gets!

 

If you apply a colour to the text then add the Gaussian blur layer with multiply, you will see that the text become darker and the blur around the text is lighter, or the text's original colour as there are no colour pixels under the blur to blend with. This gives it a halo type effect. This is what I would expect to happen, I'm not really sure of what outcome you were expecting.

 

As I said your post has confused me slightly so if I am missing something out please feel free to provide further information


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Sorry for the confusion – I just did some more tests and it turns out it might have been on my part.

 

What confused me was that with "Transparent Background" off, the white background is not considered and thus multiplying blurred text on top of itself will have no effect, which made me assume that no blending for effect layers was supported at all. However, creating any kind of background layer (such as a white rectangle on top of the implicit standard white document background) will actually make the effect show up as expected.

 

So the fact that the white background is not blended like a layer tripped me up.

 

Still, if I create a document (irrespective of the "Transparent Background" setting), create some black text, make a copy of it, blur that copy and set it to multiply, the result will be different from creating a document, creating some black text, adding a Gaussian Blur filter layer on top and setting that filter layer to multiply. 

 

The question is, should that be the case or not.

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Hi Peter,

 

The white background won't be used in blending - that part is by design. The reasoning is that using the white BG is often intended as the "paper" onto which the design will be printed - hence no blending would take place at print time..

 

The compositor actually renders everything onto a transparent background, then as a final step, mattes the result with white (soon this colour will be customisable)..

 

I do think their is a subtle bug to do with blending filter layers though - so I'll look into that..

 

Thanks,

 

Andy.

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