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Weird Halo...

Posted: Tue, 20th Oct 2009, 4:51pm

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theclone56

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I'm working on a forest shot in Visionlab, and I've got some trees which I've cut out in Photoshop, and saved them as a PNG to preserve the alpha channel. So I dropped them on my timeline, no problem, background's all keyed out. The problem comes when I tried to keyframe some defocus filters in order to simulate a rack focus. When the defocus filter is applied to the tree elements (three separate images) I get this sort of white haloing around the layer. It's just a semi-transparent blurred white line, or something.

I thought maybe it was some sort of pixel wide thing on the original image, so I eroded white a couple of pixels. Didn't get rid of it. The only way to make it disappear this way is to erode white as much as is possible, which... looks very bad. Then I thought it might be because of the defocus filter's bloom property, so I dropped that down to zero. Still got the white halo. Then I tried replacing the defocus filter with a guassian blur, but the same thing happens. I'm stumped on this one, anybody know how to get rid of that?
Posted: Tue, 20th Oct 2009, 6:25pm

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spydurhank

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Did you actually cut arund the tree or did you erase around the tree?
If you erased rather than cut... then the alpha chanel may not be as clean as you think. There could be semi transparent artifacts on the alpha channel.
Posted: Tue, 20th Oct 2009, 9:05pm

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theclone56

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I erased around the tree, then used the magic wand tool at 250 tolerance to select the whole tree, then refined the edge, feather, smooth, contract, etc. Then I layered that via copy and deleted the old layer. If it were some sort of artifact around the edge, wouldn't the erode white solution have taken care of the problem?
Posted: Wed, 21st Oct 2009, 1:06am

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spydurhank

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I believe that it should. Do you think you could post a small video clip or a photo? This will help to identify the issue.

A few more questions for you.
1. Does the tree pic still have the "halo" when you first place it on the timeline Or only when you apply the diffuse or de-focus filter to it?
2. Are you applying the filter to the trees only or to all of the footage?

If so... I suggest trying a Gaussian blur filter rather than the diffuse filter. The diffuse filter tends to cause the footage to "bloom, become very blurred and bright" That may be what's causing the halo effect that you mentioned.

Anyway... if you're trying to do what I think you're trying to do... The Gaussian blur filter will create a much more realistic depth of field type effect. But like I said before, I can't be sure of what you're actually trying to do so let me know and we'll try to squar that away for you.
Posted: Wed, 21st Oct 2009, 1:20am

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theclone56

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All I'm trying to do is a simple rack focus, with foreground stuff in focus for a start, background blurred, then it switches. And that aspect of the clip is working fine, it's just this halo that's throwing it all off.

In answer to your questions;

1.) There's no halo when the trees just dropped into the timeline. It's when the defocus is applied that the problem arises.

2.) The filter is applied to all footage, but individually, so that I can keyframe the rack focus.

As I said, I tried turning the bloom portion of the defocus filter all the way down, but it didn't ditch the bloom. And I tried a guassian blur in place of the defocus, but I'm still getting the blur.

Mask feather can be keyframed, right? If so, I could manually remove the blur, which would be okay for a short-term solution on this shot, but would be a pain in the ass to do every time I needed something blurred. I've had this happen before, so I DON'T think it's something specific to these tree elements. And I don't suspect it's got anything to do with the brightness of the element itself, because there's even a halo around a portion of the tree that is in pretty deep shadow.

EDIT - Oh, I can probably upload a picture tomorrow, if you think it'll help identify the problem.
Posted: Wed, 21st Oct 2009, 3:05am

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spydurhank

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Yeah that'll help a great deal.
Something must be acting screwy with the alpha channel on the tree pictures then. I do the same kind of thing with still images and matte paintings all the time so I'll see if I can duplicate that halo effect to better understand what's going on.

Have you tried using a grade filter with an object mask applied to the tree picture? It would look like this on your timeline.

Timeline.

layer 3. Grade object. Diffuse filter. Object mask applied to Tree picture. (the object mask uses the tree pics alpha channel to apply the grade object and other filters to only the picture, it may have to be inverted but I'm not sure just yet)

layer 2. Tree picture.

layer 1. Live footage.

Try it out and if it still doesn't work... at least it'll tell you that there's definitely something wrong with the Tree pics alpha channel.

Oh and try not using the "Erode white" key filter, that may be part of the issue since you don't need to key out the picture.
Posted: Wed, 21st Oct 2009, 3:34am

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theclone56

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Wouldn't using an object mask from the tree on a grade object set to blur just result in a crisp-edged tree with blurry details?

Also, I'm not ACTUALLY using the erode white filter, I just figured I'd try it when I couldn't get rid of the halo. Didn't work...

Though it's not just the trees that this happened to me with. EVERY time I bring in an image that I've cut out in Photoshop, when I blur it, I get a white blur going around the edge. And I've checked the files out with the zoom tool in Photoshop, I can't see any sort of a white border or anything. Just my picture.

I tried an experiment. I thought maybe it was the feathered edge that was causing the glow. So I just created a red oval, in Photoshop, to bring into Visionlab and see what happens. Just used the shape tool, simplified it, nothing fancy, no feathering. Had a nice, solid red edge. Saved it as a png, brought it into Visionlab. It ditched the background per the alpha channel, and when I did a guassian blur on it, I got a big white glow around it. So I have a feeling it's Visionlab, and not me. Unless I've somehow managed to mess up applying a guassian blur.

I've uploaded the original oval as well as a Visionlab render of the result.



Posted: Wed, 21st Oct 2009, 3:54am

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spydurhank

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Oh wow!
That is weird. How much blur are you using?

I just tried it with a cut out pic that I just made but I'm not getting the halo effect. Well I do kinda get an effect similar to yours but only if I set the blur and bloom really high on the defocus filter. Try a lower setting, oh and I'm also using a "Tiff" format for the picture though. That format does not degrade the qality of the pic and peserves the alpha channel.

Can you save your pic to that format in Photoshop? See if you can and give it a try.
Posted: Wed, 21st Oct 2009, 4:02am

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theclone56

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I just tried a red oval as a TIFF and I didn't get the white halo when I did the guassian blur on it. Then I converted my tree to a TIFF and the result was the same, no halo. Guess it must be something to do with PNG's. I'll be switching over to TIFF's, then. Thanks for chatting this out with me.
Posted: Wed, 21st Oct 2009, 7:50am

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spydurhank

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That's awesome! biggrin
As long as you got it sorted out... that's all that really matters! biggrin
Now you can continue with your project.
Hope to see some of your work as soon as you're done adding your effects. So congrats to you, and don't hesitate to ask if you happen to run into anymore speed bumps.

Best of luck.

Frank.

p.s.
Sorry... I meant "preserves" the alpha channel.
I missed the spell check on that one. crazy
Posted: Wed, 21st Oct 2009, 4:36pm

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pscamm

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Got something to add to this which produces a similar undesirable effect with a halo.

1. Pop in a background of your choice, something on the darker side will show the issue better.

2. Layer on top any greenscreen clip you have and key out the green in the usual way until your happy with the results (looking good so far ?)

3. So you decide that your greenscreen extraction is a little sharp or whatever and you want to blur/defocus it a little....Apply either Gaussian blur or the Defocus filter and whack the amount up to around 50'ish

In commeth a green halo

- When you think about the simple scene you have just produced (simple background with simple greenscreen extraction on top), if i were to apply a blur of any kind or a defocus to the greenscreen layer/clip i would expect the blurred edge of my key to mix/merge into the layer below (background clip) - Would you agree ??? What is actually happening is the blur/defocus is mixing with the greenscreen you have just keyed out on the same layer.

Make sense ???

The problem 'theclone56' experienced with the alpha (probibly inverted) the part automaticly keyed out by the alpha in essence is pure white so, as in the above example the defocus filter is bleeding in the colour which is made invisable by the alpha exactly the same as what is happening in my example above.

This should'nt happen...Right ?
Posted: Wed, 21st Oct 2009, 4:44pm

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Joshua Davies

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pscamm - You need to use the spill suppression filter.
Posted: Wed, 21st Oct 2009, 5:04pm

Post 13 of 13

pscamm

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Thanks schwar,
Did mean to add that fact in there too but forgot ref the green screen example i gave

Bearing in mind the spill suppressor deals with red, blue and green spill im not sure it will solve theclone56's white halo issue

Thanks
Paul