How to limit Filter or Adjustment layer to certain colour?

[thomaso]

This recent thread about a blurred text background within a Table text layer makes me wonder whether it is possible to exclude the black (100 K) of text + table lines and let the effect only affect the colour of the text background (e.g. Character Background or Paragraph Decoration) without using additional layout objects?

I tried with a blend mode for the Filter (e.g. Darker Colour) but with insufficient result:

A Procedural Filter comes to my mind but I don't know if or how this would work and need to get scripted.
If colour wouldn't work, could this be set to affect a specific text style property only ("background" / "decoration") – ideally without rasterizing the black text?

Any hints?

[Dan C]

Hi Thomaso, 

The only real way to ensure the 100k text remains 100k text with an effect like this applied is to overlay a duplicate without the effect on, as gaussian blur is an inner and outer effect (unlike say outer glow/outer shadow which is essentially placed behind the object and has no effect on the layer it's applied to and only adds to it).

Lee

[thomaso]

Thank you, @LeeThorpe, Yes, to maintain a black as 100 K any rasterization has to be avoided. Sorry, obviously I was not clear in my question and example.

I rather have a more general idea in mind: To filter (= limit) the effect of an adjustment or filter layer to a certain colour or colour area. I still have the feeling it would technically be possible but have no idea how, – unless with masking the affecting layer to the areas of the affected layer of the wanted colour(s), e.g. with a pixel selection, which, on the other hand, would also limit a blur effect to the selection edges and thus not blur them. For instance:

1. A coloured target layer …

2. … should get blurred …

3. … but only for certain colours, e.g. cyan.

4. I see a way to filter the colours + to blur the result …

… but now magenta and yellow are blocked – while I want to keep them visible but just not affected by the blur layer.

I don't see a way to combine blur & colour filter in the way that one limits the other. I am aware that a filter or effect layer itself has no colours, respectively can get masked in grayscale only, so I guess masking is not the point here.

With other words, I want to apply the blur effect to the output of the colour filter but without blocking any colour from the total output. Or: Use the output of one as input for the other but not as filter for the entire setup.

Maybe I have an error in my thinking, but were?

[NotMyFault]

Normally you use one of the following methods:

• Blend range applied to blur filter, to exclude colors of layers below (destination)
• Photo: live mask, with hue range
• Photo: use one of the color channels as „key“
• With help of PT filters, you can transform color values so they are mapped to one specific color values, (for use with blend range).
•  

 

[thomaso]

Thanks, @NotMyFault! Your hints enable me to exclude M + Y from the blur filter. But I am afraid I don't understand / don't know the detailed workflow for the steps / options after "Blend range". – Maybe you can occasionally upload a V1 example document or edit the attached V1 document accordingly?   v1105 filtering a filter.afpub

Do I understand right that a pixel mask is required to achieve a result that doesn't filter only by the channels C, M, Y but includes for instance green in this sample to the blur?

[NotMyFault]

Forgot that you using v1 only.

What you want is a bit complex to realize as non-destructive workflow, because you want to use the source layer for 3 different purposes:

1. as source for blending (the RGB Chanel’s)
2. as source for creating a mask (essentially alpha channel), but based on RGB color values.
3. and we need the result of the blur filter (RGB values) applied to the source layer

The problem is that it is next to impossible to combine 2+3 back again into one object non-destructively. The blend formula makes this practically impossible, and Affinity does not offer a non-destructive „apply image“ functionality (which is what we need to combine both). Apply image provides essentially a custom blend formula.

A destructive workflow would be:

1. copy source layer
2. apply PT filter to map selected hue into all RGB channels (for simplicity), and set alpha to 1.
   1. my PT filter witch create hue value from RGB is bases, then add some kind or range filter which gives 0 for „outside“ values and 1 for „inside“ values. The leap and step function will do. I can create such a filter (but need some free time)
3. Merge / rasterize result
4. rasterize to mask
5. add blur filter, using the mask

It might be possible to create a result similar (not identical) with multiple helper layers (groups, alpha tricks) and essentially duplicates of of the source layer (either by symbols from designer, or linked layers from photo). I tried many times, and couldn’t find a full solutions.

Some minor progress:

• Non-destructive blur filter restricted to alpha channel (but this uses a unfixed bug)
• compressing RGB/A channels to free one of them for different purposes
• mis-using alpha channel as „z-axis“ to allow 2.5D blending of layers (overruling the layer stack sequence).
  This might be a basis for your request, but is has several limitations and drawbacks, e.g. anti-aliasing may break, and uses RGB/32 to have some spare bits to store z-values in addition to alpha.

[NotMyFault]

Here is a v1 file envisioning the idea. 
adjust the color contribution of the channels mixer adjustment to alpha. This will show those colored areas excluded from blur.

• for pixel layers only (use symbols to allow any layer)
• limited to rgb/cmyk channels only (cannot choose any hue). Needs another PT filter to allow selected a hue range.

 

restricted.afphoto