Alpha channel still kind of useless in Resolve

Few things are as frustrating in Resolve as the handling of alpha channels. It can handle alpha information as either 0% or 100%, nothing in between. You want to add a glow to some letters or any element? No way. You'll see the part of the glow that falls inside the letters, but nothing outside.

It's not that at least it's useless for external sequences or videos that have a variable alpha channel, but at least it's fine when you apply FX in Resolve or the Fusion page. It doesn't work for those either, while every other NLE works just fine for that. Whether it's imported sequences, videos or bundled FXs, transparency is always shown correctly.

Since this forum runs on ancient software that only allow three pictures per post and multiple steps to post each, I made the examples all in one picture and uploaded that instead, having to shrink it to less than 1 MB because that's the maximum the forum allows:

Alpha bug for forum.jpg (976.59 KiB) Viewed 678 times

Are we ever going to have proper alpha channel interpretation in Resolve? Because if all people ever need are hard edges for alpha text or images, fine, but I'm guessing that quite a lot of people need a glow every now and then, and several other situations that need variable transparency levels, not just totally transparent or totally opaque.

Every other NLE I used in the last 25 years can show alpha just fine, is it too much to expect that Resolve can do it?

[Peter Chamberlain]

Post your source clips an im sure someone will show how to do it.

Post your source clips an im sure someone will show how to do it.

Peter, I think my explanation is super clear, and this has been the case at least since version 19 if not before, but I used 18.6 very shortly before 19 came out.

I mean, it's clear to me that Resolve can't read any alpha information that is below 100%, it simply interprets it as 0%.

I've run into similar things, particularly with Resolve FX effects. Applying Resolve FX glow to a clip with alpha will leave you choosing between the alpha being becoming black or the effect being limited to the opaque area.

There are some hacky ways around this, but your best bet is to use a Fusion effect template for glow, and other effects with similar issues.

I've made a quick Fusion effect template as an example: https://pastebin.com/raw/0MtdvVX5

It is simply a Fusion Glow node with alpha processing disabled. It should apply a glow, without nuking your alpha, as you would expect.

If you save it to your effects templates folder as "Simple Glow.setting", it will be available in the edit page as "Simple Glow." The effects template folder can be located by pasting the following into the console opened via Workspace > Console:

Code: Select all

print(fusion:MapPath("Templates:Edit/Effects"))

I'm running v20 Studio B2. I hadn't really used linear keys in a while when I saw your post. I train on broadcast production switchers (specifically Sony MVS/MLS series) and I take a lot of graphics and videos with me when I go (many times, the CG and other stuff isn't even hooked up yet).

I put, into a Resolve timeline. all the items that I use, specifically items that are linear keys with varying levels of transparency in the key signal. Some are designed for "straight" some are designed for "premultiplied." All my graphics work on Resolve exactly like they work on the production switchers, including items with glows.

I attached a photo of the screen shot. In it there are three layers on top of the cat. The bottom-most is a lens flare graphic, which is designed as a straight key. There are glows around all the rings. The next layer is the CG. You can see opaqueness on the fonts, the "tabs" on the upper left and right and the ticker at the bottom. But you can see the linear key transparency in the middle section. this was designed to be used as a premultiplied key. Lastly the over-the-shoulder graphic (also designed as a premultiplied key) has opaqueness in the picture and on the backdrop ramps from totally opaque to about 40% transparent. On the bottom right is a glow, which can be seen extending into the background.

Is there anything else I can try to help diagnose this with you? I hope I have interpreted your issue correctly.

I've run into similar things, particularly with Resolve FX effects. Applying Resolve FX glow to a clip with alpha will leave you choosing between the alpha being becoming black or the effect being limited to the opaque area.

There are some hacky ways around this, but your best bet is to use a Fusion effect template for glow, and other effects with similar issues.

I've made a quick Fusion effect template as an example: https://pastebin.com/raw/0MtdvVX5

It is simply a Fusion Glow node with alpha processing disabled. It should apply a glow, without nuking your alpha, as you would expect.

Thanks, but are we talking Fusion Studio or Fusion page? If I paste this into the Fusion page, I get a glow group node, but it only shows the glow inside the text. I need to enable alpha in the node to get it to show the glow, and it does, and that transfers to the edit page as well, which I'm confused about, because earlier I tried different glows from the Fusion page, and in all of them I was getting the result I've shown.

But the glow I use most of the time is Xglow, which I know is not native, but it's my favorite glow by far. And if for some reason it wouldn't work from the Fusion page, I don't mind doing that part in Fusion Studio, exporting an EXR sequence and bringing that into Resolve. But obviously that I cannot do because what happens is what I showed above.

So I don't get why sequences or videos with alpha channel are not shown properly in Resolve. Do I need to try other codecs or picture formats besides EXR and Prores 4444 XQ?

I'm running v20 Studio B2. I hadn't really used linear keys in a while when I saw your post. I train on broadcast production switchers (specifically Sony MVS/MLS series) and I take a lot of graphics and videos with me when I go (many times, the CG and other stuff isn't even hooked up yet).

I put, into a Resolve timeline. all the items that I use, specifically items that are linear keys with varying levels of transparency in the key signal. Some are designed for "straight" some are designed for "premultiplied." All my graphics work on Resolve exactly like they work on the production switchers, including items with glows.

Is there anything else I can try to help diagnose this with you? I hope I have interpreted your issue correctly.

OK good. I still haven't installed beta 2 since it just came out, but let me ask you, all these items with several degrees of transparency that you show there, what is their format?

I'm running v20 Studio B2. I hadn't really used linear keys in a while when I saw your post. I train on broadcast production switchers (specifically Sony MVS/MLS series) and I take a lot of graphics and videos with me when I go (many times, the CG and other stuff isn't even hooked up yet).

I put, into a Resolve timeline. all the items that I use, specifically items that are linear keys with varying levels of transparency in the key signal. Some are designed for "straight" some are designed for "premultiplied." All my graphics work on Resolve exactly like they work on the production switchers, including items with glows.

Is there anything else I can try to help diagnose this with you? I hope I have interpreted your issue correctly.

OK good. I still haven't installed beta 2 since it just came out, but let me ask you, all these items with several degrees of transparency that you show there, what is their format?

The are a .png sequence

are we talking Fusion Studio or Fusion page?

The Fusion page - but you don't even need to go to the Fusion page (unless you want to create effect templates).

If you save a .setting file containing the text of the pastebin, and ensure it is in the directory printed after putting this into the Resolve console:

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print(fusion:MapPath("Templates:Edit/Effects"))

It will be available as an effect directly in the edit page:



With all the necessary inputs exposed:



With regards to:

Code: Select all

If I paste this into the Fusion page, I get a glow group node, but it only shows the glow inside the text. I need to enable alpha in the node to get it to show the glow, and it does, and that transfers to the edit page as well, which I'm confused about, because earlier I tried different glows from the Fusion page, and in all of them I was getting the result I've shown.

For scenarios where the falloff is being clipped, try putting this node immediately after a glow node:

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{
   Tools = ordered() {
      BrightnessContrast1 = BrightnessContrast {
         CtrlWZoom = false,
         Inputs = {
            ClippingMode = Input { Value = FuID { "Frame" }, },
            Red = Input { Value = 0, },
            Green = Input { Value = 0, },
            Blue = Input { Value = 0, },
            Alpha = Input { Value = 1, },
            Brightness = Input { Value = 0.001, },
            ClipBlack = Input { Value = 1, },
            ClipWhite = Input { Value = 1, },
            PreDividePostMultiply = Input { Value = 1, }
         },
         ViewInfo = OperatorInfo { Pos = { 1540, -49.5 } },
      }
   },
   ActiveTool = "BrightnessContrast1"
}

It is a brightness/contrast node that only processes alpha, with a +0.001 to brightness. It seems to "normalise" alpha in all the scenarios I have tested (providing the alpha data exists, but is not being used).

If that works, you could set up a Fusion effect template with both your glow and the brightness/contrast for easy use without having to move over to the Fusion tab for every glow.

I ran into very similar frustrations with Fast Glow and XGlow a few months back. Passing the output of an Fast Glow/XGlow node to Resolve FX transform would step the alpha, clipping all falloff. The alpha data was still there, it just wasn't being picked up by Resolve FX transform.

@Peter, I don't think it's a skills issue.

Here's a demo using the built-in Text+ tool to show how some OpenFX handle alpha.

Simply adding a glow to a clip will make it 100% opaque, removing any alpha information on the clip:

Adds glow but messes with

Glow - No Alpha.jpg (200.29 KiB) Viewed 489 times

Unchecking the Use Alpha option will bring the alpha information back, but it removes the glow:

Keeps alpha but removes glow

No Glow - Alpha.jpg (373.69 KiB) Viewed 489 times

I think the OpenFX glow needs to better handle the compositing of what's underneath a clip.

I'm also seeing the Use Alpha checkbox of the Glow effect applied to a Text+ clip turn the underlying clip black.

Studio 20b2 for Windows.

@Peter, I don't think it's a skills issue.

Here's a demo using the built-in Text+ tool to show how some OpenFX handle alpha.

Simply adding a glow to a clip will make it 100% opaque, removing any alpha information on the clip:

Glow - No Alpha.jpg

Unchecking the Use Alpha option will bring the alpha information back, but it removes the glow:

No Glow - Alpha.jpg

I think the OpenFX glow needs to better handle the compositing of what's underneath a clip.

It does, but this seems to me like it's beyond just the glow effect. It's a case of Resolve not handling transparency levels properly. If I export from any program, call it Fusion Studio, After Effects, Apple Motion or similar, anything with an alpha channel, using a codec that supports it obviously, any NLE should read the transparency level in each single pixel in the frame for what it is. If it is 100%, it's completely opaque, if it's 60%, it should show it as 60% opaque, or 40% transparent.

But Resolve doesn't do that, that's what they need to fix. It's not a matter of the 20 beta 1 or 2 version, it's been the case since at least 19, so I have to assume it was always like that. Not the kind of thing that gets broken with a new version.

The are a .png sequence

Thanks, I'll give that a try and report back as soon as I get a chance.

As far as I can tell this is a problem that manifests itself when the glow (or whatever) is additive, meaning it has zero alpha but nonzero RGB channel values. This additive part would get lost when there is a premult operation done after applying the glow as it will be zeroed out due to glow being only in RGB channels, not in alpha. If glow were solid, with associated alpha, it should work…?

Additive effects with zero alpha are perfectly valid thing, but it only works if it isn’t killed with premulting. Ergo, it only works if element is expected to already be in premulted state. Someone most probably knows the schematics and pages in manual that tell the image state when an effect is applied, I don’t so its just a guess that this is where it goes wonky.

As far as I can tell this is a problem that manifests itself when the glow (or whatever) is additive, meaning it has zero alpha but nonzero RGB channel values. This additive part would get lost when there is a premult operation done after applying the glow as it will be zeroed out due to glow being only in RGB channels, not in alpha. If glow were solid, with associated alpha, it should work…?

Additive effects with zero alpha are perfectly valid thing, but it only works if it isn’t killed with premulting. Ergo, it only works if element is expected to already be in premulted state. Someone most probably knows the schematics and pages in manual that tell the image state when an effect is applied, I don’t so its just a guess that this is where it goes wonky.

The thing is, in every other NLE, this is not a problem. You have a background clip in track 1, then you throw a still or a sequence, or a video that has an alpha channel with varying degrees of transparency, and it looks like it's supposed to look, whether it's a glow, a shadow or anything else that goes out of the boundaries of the object in the upper clip, and increases in transparency until it's completely transparent, every other NLE I used shows that. Sometimes at worst you may have to change the alpha mode from premultiplied to straight or the other way around, which is not often, but one way or the other, you see the upper clip as it's supposed to be.

That needs to be fixed in Resolve, rather than trying to figure out workarounds.