Issue with Alpha when compositing

[MBLV]

Here's the set up:

I'm rendering images in 3ds Max. When I go to change the background in Affinity Photo there is a white matte that I cannot get rid of. It seems like the alpha channel is not being correctly read as premultiplied.

I have tried using Filters->Colors->Multipy by Alpha and Remove White Matte, and they seem to soften the effect, but it's still there.

I've tried the image saved out of 3ds Max as a PNG, EXR, and TIFF, all with the same results.

Attached is an example image with a solid color fill on the layer below.

Is this a bug? is there some setting or filter I'm missing?

Thanks!

[NotMyFault]

Hi, 

could you upload the .afphoto file and/or the import files?
Remove white matte could be the culprit, we might find better solution.

Is it possible to export the alpha channel separately from 3Ds Max as grayscale layer/file?

 

[MBLV]

I isolated the tree and made a simple comp. The problem gets much worse and more noticeable when color adjustments are added to the layer, in this example i added some curves. also included on a separate layer is the alpha pass saved separately from Max.

Thanks for taking a look.

treeTest.afphoto

[NotMyFault]

Thanks for the file.

For me everything looks perfect (in the sense of no bug).
 

If you use the alpha channel instead of master in the curves adjustment, you can improve the alpha blend to look more natural, by reducing partial alpha values. 

I’m on iPad currently, UI on Desktop might look different  

What result do you want to achieve for the green leaves on blue background?

The tree image includes them with partial alpha, leading to unpleasant looking results (but technically correct).

 

 

 

 

[MBLV]

The point here of using the curves is as part of the color correction, so i need it on the master channel. And (in this case anyway) i need the curve upward.

I suppose i could add a second curves set to alpha and pull it down, but that starts to cut into the edges, or the white edging comes back

 

 

Edited July 8, 2021 by MBLV

[NotMyFault]

To solve smooth the edges, I used the alpha channel, detect edges, rasterized to mask, and applied this mask to a Gaussian blur of 0.1 or 0.2 px. This look better, I often blur mask edges using different methods to achieve a smooth transition. 
had to recolor the background as rename on iPad did not work and I need to find my version visually 

 

treeTest.afphoto

Edited July 8, 2021 by NotMyFault

[MBLV]

I appreciate your effort. I really do.

But it doesn't solve the issue, and it goes back to looking even worse when I turn back on my Curves for color correction.

There shouldn't be any hoops to jump through or a bunch of tricks to apply for this. 

It works cleanly in PShop, Nuke, and DaVinci by just putting the image over a background layer.

 

Anyone else have any idea or have had this happen?

[Muokkaa]

Hi, 

 

Same situation here but with Redshift and Cinema 4D. Looks like Affinity Photo doesn't read alphas and masks properly when importing from external software. 

In my case, I'm extracting some alphas from an EXR. Photoshop perfoms really nice, but Affinity Photo creates some kind of halo expanding the masks. As MBLV said, there shouldn't be any hoops to jump through or a bunch of tricks to apply for this, it should be easy for Affinity as it is for other softwares.

I have attached an image to show you how the same file looks in Affinity and Photoshop. Looks like this is a bug, hopefully it's solved soon.

 

[Muokkaa]

I have been digging into the forum and looks like this is a problem that Affinity haven't solved yet. I have found some threads talking about the same situation with alphas and I found zero solutions for the issue. 

It's a pity because I just used Photoshop for 3D retouching and Affinity Photo looked like the best alternative, but it's not. I'm not saying is a bad software but, it still needs some improvements to be a good professional choice. 

If you find a solution for this, please keep me posted.

 

[NotMyFault]

It would really help if somebody impacted by this issue could provide example files which help to reproduce the actual difference between PS and Affinity Photo.

With reproduce i mean having the result from PS and Affinity as separate layers (from imported files)  within one Affinity document, to numerically calculate the RGBA delta with perfect pixel-aligned layers.

The jpeg compressed screenshots from PS (without alpha) are unfortunately insufficient for this approach.

I have no access to PS and depend on export files.

Ideally, the set of file should contain:

• the source file to be imported
• An PS export in uncompressed alpha-capable file format (TIFF, PNG) of the imported source file
• An PS export in uncompressed alpha-capable file format (TIFF, PNG) of the imported file with a contrasting primary color fill layer blended
• An PS export of the alpha channel as greyscale layer

Since AP 1.9.1, there is an unsolved issue adjusted the alpha channel, see https://forum.affinity.serif.com/index.php?/topic/137301-curves-alpha-not-working-when-child-layer/&tab=comments#comment-757081.

This issues might be related. Even if not related, the issue blocks possible workarounds which depend on being able to use nested alpha channel adjustment layers.

 

 

 

 

[NotMyFault]

After looking again into the test file from @MBLV i can spot a difference between two layers (after alpha converted to GS):

The are becoming identical only when i apply a gamma correction A^2.2  to the alpha layer.

Unfortunately based on the alpha adjustment issue mentioned above, the correction must be applied as destructive filter (instead of nested live filter).

Can you please test if the blending looks OK then?

 

You might find these tutorials interesting:

https://www.youtube.com/watch?v=P8peGDf4HzA

https://www.youtube.com/watch?v=KuMHg1wzWzA

 

Edited July 13, 2021 by NotMyFault

[Muokkaa]

Hey @NotMyFault

Thank you very much for your help. Since I can't send that file cause is a client thing, let me prepare a scene with some similar elements and render, and I will share it here with you. 

Also, thanks a lot for those links, really helpfull the one about 3d render composition. 

I will share those files as soon as I have them ready to go.

Cheers!

[NotMyFault]

Great. It would help if you include at least one linear greyscale area, e.g 256 pixel wide, 0-100% gray (0/255 to 255/255).