What does the alpha option in Curves do ?

[ESPR]

In Gimp i can manipulate transparency in Blur (retract, expand, shape) with an Alpha Curve.

Although AP has an alpha option in the Curve Adjustment, it doesnt seem to do anything.

Here is a screenshot of what i can do in Gimp:

 

The only way i can recreate this with Affinity Photo is when its in grayscale.

[R C-R]

Are you sure your RGB document has some variation in its alpha transparency like in the first Gimp screenshot?

When it does, as in this simple Alpha curve adjustment.afphoto example, I get results very similar to those you get in Gimp.

[ESPR]

22 hours ago, R C-R said:

Are you sure your RGB document has some variation in its alpha transparency like in the first Gimp screenshot?

 

Thanks for testing this and attaching the demo !

I dont know what went wrong with my experiment, but now it works as expected. Great !

 

I do have another question, however:

in your demo, the Adjustment layer was on top but when i try to nest the curves adjustment as a child layer, the effect is no longer working.

Is that normal ?

If so, how do i prevent the Adjustment from applying itself to all layers ?

[Old Bruce]

28 minutes ago, ESPR said:

I do have another question, however:

in your demo, the Adjustment layer was on top but when i try to nest the curves adjustment as a child layer, the effect is no longer working.

Is that normal ?

If so, how do i prevent the Adjustment from applying itself to all layers ?

Same questions. Is this some sort of bug?

[R C-R]

23 minutes ago, ESPR said:

I do have another question, however: when i try to nest the curves adjustment layer as a child, the effect is no longer working.

Is that normal ?

If so, how do i prevent the Adjustment from applying itself to all layers ?

I don't know if the adjustment not working as a child layer is a bug, by design, or what, but the only way I have found for the adjustment just to apply to the layer immediately below it is to use the "Merge" button in the adjustment window to destructively 'bake' the transparency into it, if that makes any sense.

Maybe someone else has a better way to do that.

[ESPR]

I just noticed it also doesnt work when there is a solid background below the transparent layer with the blurred object.

[lepr]

17 minutes ago, ESPR said:

I just noticed it also doesnt work when there is a solid background below the transparent layer with the blurred object.

Affinity apps are riddled with years old rendering and compositing bugs which, it would seem, are of no interest to the developers.

A couple of workarounds (there are others) for your problem: 

• stack the Pixel object and alpha Curves Adjustment in a Normal mode Group, or
• put the Pixel object in a Normal mode Group and mask-nest the alpha Curves Adjustment in the Group.

alpha curve.afphoto

[ESPR]

28 minutes ago, anon2 said:

Affinity apps are riddled with years old rendering and compositing bugs which, it would seem, are of no interest to the developers.

 

Thanks for the demo !

You know i got into Affinity because i was fed up with some of the problematic limitations and stupid designchoices i found in Inkscape and Gimp and never warmed up to PS and AI, but it seems all programs have their flaws, pros and cons.

[JimmyJack]

Some additional info:

Both nested and stacked versions work if you're using a Blur live filter. Of course this only helps if you're in APh...no blur filter in Designer.
In the nested version they have to be in the mask position....not just children. & .... notice the different order in each.
(Items #s 7465 and 7466 on the must remember idiosyncrasy list 😂.)

[Alfred]

56 minutes ago, JimmyJack said:

Both nested and stacked versions work if you're using a Blur live filter. Of course this only helps if you're in APh...no blur filter in Designer.

You can only add a Blur live filter in APh, but if you save the document and open it in AD the filter will still be live.

[JimmyJack]

19 minutes ago, Alfred said:

You can only add a Blur live filter in APh, but if you save the document and open it in AD the filter will still be live.

Yes, I realize. But I try to avoid cross pollination if at all possible. It appears to introduce instability. Seems like it's just a matter of time before things tend to go wonky because of it.
At least that's been my experience. Especially when trying to incorporate perspective into Designer 😁.

[ESPR]

If anybody is wondering what this is all about: i used this technique to make bumpmaps for special bevels in Gimp, but its also good for halos and such.

To some degree this is built into Affinity's Bevel fx as 'Profile', but the 'Live Lighting' Filter also accepts bumpmaps (these have to be in grayscale, i believe).

 

I also made this speakerlike structure and texteffect with this technique, a few years ago: