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Alpha channel and jaggies in FCP 5

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Robert Withers
Alpha channel and jaggies in FCP 5
on Sep 29, 2013 at 7:11:58 pm

Alpha channel and sawtooth artifacts

I know little about alpha channels, and the FCP 5 manual is not helping much with some interlaced NTSC footage, lower field dominance. I'm editing in FCP5 because for various reasons I can't export/import an XML of this to Premiere.

Here's what I found while editing on a timeline:

1. My images look jagged on a video monitor, especially images with vertical or horizontal lines. Images with text look very jagged.

2. When I Modify a clip to change from Alpha Type None/Ignore to Straight, the images and text clean right up. The jaggies are gone, text is clear, no image wavering.

3. Shall I do this with the entire timeline? Are there implications for later processing, such as saving a Quicktime, converting to HD 23.98 progressive, importing into a Premiere timeline, and outputting to various release formats?

4. This Modify to Straight procedure doesn't work for the jagged edges of a text clip, white on black, where the Alpha Type is set to black. What does work is setting the view in the Viewer options to Alpha instead of RGB or Alpha + RGB. But will this view selection carry over to making a QT file of the timeline? The properties of the clip don't change, still show Alpha as Black.

I'm in over my head with this, as so often. Can anyone help?

Thanks,
Robert



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Robert Withers
Re: Alpha channel and jaggies in FCP 5
on Sep 30, 2013 at 12:31:54 am

Clarification: It's not on a video monitor that I see the jaggies, it's on an HD television that I feed the signal to through firewire and a miniDV camera, into an S-video input. (4:3 aspect ratio) My theory is that I'd like to see what the movie will look like in the form that people will see it--played back from a DVD on a television.
No jaggies appear on the computer display in FCP--only on the television.
Does this make any sense?
R



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Rafael Amador
Re: Alpha channel and jaggies in FCP 5
on Sep 30, 2013 at 1:20:16 pm

[Robert Withers] "2. When I Modify a clip to change from Alpha Type None/Ignore to Straight, the images and text clean right up. The jaggies are gone, text is clear, no image wavering. "
If you check "None/ignore', you are voiding any alpha channel that might be on the picture.
If checking "Straight", things work, that tells you that your clips/graphics have Strait Alpha and that the way to go.
Straight Alpha is the most usual option (FC exports and Photoshop exports Strait Alpha).

[Robert Withers] "This Modify to Straight procedure doesn't work for the jagged edges of a text clip, white on black, where the Alpha Type is set to black. "
If that stuff has been exported Premultiplied to Black or White, you have to check those options.

You need to change the Alpha BEFORE putting things on the time-line.
Change you make in Browser do not take effect on the stuff that is already in the time-line.


[Robert Withers] " What does work is setting the view in the Viewer options to Alpha instead of RGB or Alpha + RGB. But will this view selection carry over to making a QT file of the timeline? The properties of the clip don't change, still show Alpha as Black."
Those are just Preview options.
Things have to look OK with the Canvas set in RGB.
That's what you gonna get on exporting.
rafael


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Robert Withers
Re: Alpha channel and jaggies in FCP 5
on Sep 30, 2013 at 4:48:36 pm

Thank you, Rafael.

My Visual Quickpro Guide also tells me that "FCP video clips automatically have alpha channels assigned to them." So I like your answer that Straight Alpha is OK and that it's a standard export format for FC. It seems like I can set all the clips in the timeline to Straight Alpha, a little rendering goes on, and they all look good on the HD television.

I still don't know what's really happening--it almost likes like the image is being deinterlaced, but I think you're saying if it looks good it is good.

The text images are a slightly different story. When I first create them, they show a green line in the timeline and look fuzzy on the TV. But when rendered in the background they look clear on the HD television (Even though a little fuzzy on the Canvas.)

Still wondering what straight alpha really means. I hate mysteries when trying to use the technology. Of course mysteries are good in the final program.



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Robert Withers
Re: Alpha channel and jaggies in FCP 5
on Oct 2, 2013 at 4:12:16 am

OK, I've discovered that all the shots in this timeline have the wrong alpha type (none instead of straight). And that it's causing the jaggies. So I need to modify all the clips in the timeline (which have been mostly edited from subclips). I can't seem to do it by selecting all. Is there a way to modify them all instead of each of 750 clips one by one?
I need to finish this in FCP 5.5 because I can't XML import it into Premiere CC, which I'm working in now, because the subclips don't export.
Oh I hope someone has a solution.
Cheers,
Robert



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Rafael Amador
Re: Alpha channel and jaggies in FCP 5
on Oct 2, 2013 at 2:59:17 pm

[Robert Withers] "My Visual Quickpro Guide also tells me that "FCP video clips automatically have alpha channels assigned to them.""
So, don't trust your Visual Quickpro Guide.
To have an Alpha channel, the first thing you need is a codec that supports Alpha channel.
Most video codecs DO NOT Support Alpha channel.


[Robert Withers] "OK, I've discovered that all the shots in this timeline have the wrong alpha type (none instead of straight). And that it's causing the jaggies. So I need to modify all the clips in the timeline (which have been mostly edited from subclips). I can't seem to do it by selecting all. Is there a way to modify them all instead of each of 750 clips one by one?"
Are you sure your stuff has Alpha?
What are you working with?
Where is coming from?
Are you working with graphics?
You are talking about interlaced NTSC footage.
Are you working with footage from camera?
That has no Alpha unless have been applied some key.
What codec are the footage/graphics?
rafael


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Robert Withers
Re: Alpha channel and jaggies in FCP 5
on Oct 2, 2013 at 3:53:03 pm

Thanks, Rafael. This is miniDV standard def NTSC interlaced footage shot in 2006 and imported into FCP 5.5 from tape (in maybe 2007). I don't know anything about the codec than that. NTSC standard def is a codec, right? These are not graphics, it's camera footage. No key has been applied. One or two of the shots have fade-ins from black, but most don't.

I just discovered by accident that if I change the setting of the alpha channel in FCP for individual shots from none to straight the jaggies disappear on the HD television I'm using as an output check monitor. I don't know why this works or what FCP is really doing. I've read that FCP 5 creates an alpha channel to modify things like transparency. And that this is used for fade-ins or for keying if you do that. I don't know if that's true or not. I just try to read manuals, but can't find much about this.

There is an alpha channel setting that appears when I look at the clip properties. I don't know if these clips really have an alpha channel or not. I haven't done any keying or anything to this footage. All I know is that changing this to "straight" from "none" makes the footage look better.

Rafael, thanks again for your interest in thinking about this. I'd rather not even be editing in FCP and this version of FCP but I've fine-cut 750 shots in this timeline and can't export it as XML because they're based on subclips, it seems. So I want to finish this as well as possible and then export as a Quicktime. I think. Maybe there's a better way, maybe not. I'm now working in Premiere CC, but can't get this timeline into that program.



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Rafael Amador
Re: Alpha channel and jaggies in FCP 5
on Oct 3, 2013 at 2:19:05 am

[Robert Withers] "This is miniDV standard def NTSC interlaced footage shot in 2006 and imported into FCP 5.5 from tape (in maybe 2007). I don't know anything about the codec than that. NTSC standard def is a codec, right? These are not graphics, it's camera footage."
Then the codec is Apple DV.
No Alpha going on.
You are cutting plain footage and Alpha has no role at all on this task.
You need to edit your DV footage on a sequence with the same NTSC DV settings.
rafael


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Robert Withers
Re: Alpha channel and jaggies in FCP 5
on Oct 3, 2013 at 5:48:21 am

Thanks @Rafael, this is so interesting. This is exactly what I've been doing, editing NTSC footage with the NTSC settings in FCP 5.5. But this alpha weirdness nonetheless has appeared.

If I understand what you are saying, FCP took the standard def NTSC signal from the miniDV tape in the Canon miniDV camera and somehow imported it as "Apple DV" codec. And from what I see in the clip properties info, FCP somehow created an alpha channel for this footage in this codec.

I am cutting plain footage and alpha has demanded a role in the process. I didn't create or ask for or select an alpha channel--it's just sitting there in the properties looking at me. FCP enables modifying the alpha channel in the properties to change it from None to Straight.

I discovered by accident that when I do this it removes the jaggies from the image that appears on the HD television fed through firewire and a miniDV camera.

It seems like removing the jaggies is a good thing, no?
But maybe not.

I'm inclined to to change the alpha and remove the jaggies for all 750 clips in the timeline and would rather do it as a batch than a clip at a time.

Do you understand what I am saying? I'm not making this stuff up :-) I didn't ask for no alpha channel. But it's just sitting there in the fat old Apple codec that I'm editing as native standard def NTSC. I just want a clean image without jaggies.

Maybe compressor can change the alpha from none to straight for the whole timeline--I'll do an experiment. But I don't know what this means for the footage when I'll bring it into an HD timeline. Seems like doing this alpha modification from none to straight won't in itself change the interlace, the frame rate, or the pixel architecture. But it does remove the jaggies.

I have no idea why FCP created an alpha channel for this standard footage or what it's good for. Since it's part of the FCP Apple codec I can't ignore it. What it does do to my program is create a jaggie image if I don't set it properly. Have you ever run into this?
The manuals don't say. None of them. I just want to make the picture look good, though I'm not averse to learning something about this Apple codec FCP file in order to do it.
Cheers



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Rafael Amador
Re: Alpha channel and jaggies in FCP 5
on Oct 3, 2013 at 11:02:31 am

[Robert Withers] " And from what I see in the clip properties info, FCP somehow created an alpha channel for this footage in this codec.

I am cutting plain footage and alpha has demanded a role in the process. I didn't create or ask for or select an alpha channel--it's just sitting there in the properties looking at me. FCP enables modifying the alpha channel in the properties to change it from None to Straight. "

In the "Clip Properties", you are getting "Alpha: NONE".
What else you need to understand that that footage has NO ALPHA?
The first thing you need to carry an Alpha channel, is a codec supporting Alpha.
A codec supporting "MILLIONS + COLORS".
The only video production codecs supporting Alpha that I know, are the AVID codecs.
The only Apple video production codec supporting Alpha is Apple Prores4444.

Apple DV can not carry an Alpha channel, and even if you have the option of changing from NONE to Straight/Black/White in the "Clip Properties" window, that changes nothing.
rafael


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Robert Withers
Re: Alpha channel and jaggies in FCP 5
on Oct 3, 2013 at 5:02:10 pm

Thank you, @Rafael, I appreciate your patience and the theory. I still don't understand why there are alpha indicators and choices in FCP 5.5 menus if there is no alpha in this Apple codec. Why are they there? This version predates ProRes, by the way, so they are not there to deal with ProRes codec. Maybe they are there for graphics codecs.

Also, one thing you said doesn't match what I am seeing: "changing from NONE to Straight/Black/White in the "Clip Properties" window, that changes nothing."

What I see is that it _drastically_ changes the appearance/quality of the footage as it appears on a television monitor. If there is no alpha in this Apple codec why is this happening? More important, _what_ is happening? If it makes the footage look better, don't I want to do it?

Thanks again.



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