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Canon XH Series HDV Camcorders
Canon XH G1S / G1 (with SDI), Canon XH A1S / A1 (without SDI).


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Old September 10th, 2007, 02:16 PM   #1
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25F - stairs in thin objects

I haven't used much 25F until now and here's a question about it. I get quite bad stairs in thin lines, as if 25F was interlaced (showing only another field). This happens only when a thin object is in front of bright background. But I haven't ever seen this with 50i. So am I capturing my 25F-material wrong or is this normal behavior with F-mode? I use FCP6 (HDV-1080p25 settings) to capture/edit.

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25F - stairs in thin objects-stairs.jpg  
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Old September 10th, 2007, 03:20 PM   #2
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Same here...

I have exactly the same problem, and it gets worst when you downsize it. Sometimes i use the Flicker filter to hide it a little.
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Old September 10th, 2007, 03:34 PM   #3
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I read an article stating that Canon produces it's frame mode by using a vertical pixel shift; this is because the image sensor is interlaced, and they are not able to give us true progressive. This may explain why you see the effects you are talking about. This also reduces the vertical resolution when compared to the interlaced frames. They are approximating a progressive scan.
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Old September 10th, 2007, 04:57 PM   #4
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This doesn't bother me too much as the "pixelation" around the details.
I shot some 25F yesterday and it shows the same. Could be downsampling from HD to SD (DVD). I have not checked on HD screen. And, looking directly at Parkinson (ITV?) after my test DVD I found out that the XH A1 is really a crappy camcorder ;) But they are on another budget... Don't rave. I like the A1 very much. Yet another concert to shot tomorrow!
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Old September 11th, 2007, 01:20 AM   #5
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Quote:
Originally Posted by Robert Petersen View Post
I read an article stating that Canon produces it's frame mode by using a vertical pixel shift; this is because the image sensor is interlaced, and they are not able to give us true progressive. This may explain why you see the effects you are talking about. This also reduces the vertical resolution when compared to the interlaced frames. They are approximating a progressive scan.
Yes. Sadly this might be the case. I was hoping that there is something wrong with my capturing method.
It is absolute possible to get great 25p picture from A1, if there isn't a bright background behind. I'm shooting mainly nature, so there are lots of situations when stairs appears.
I've been reading here that many of you are using only 24F. Do you have some settings or tips to reduce this problem?
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Old September 11th, 2007, 03:39 AM   #6
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It looks like it has been deinterlaced. What capture/editing software settings are you using? Do you happen to use FCP 6 with "no fields" in the settings? If so it is possible that it's deinterlacing the image.
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Old September 11th, 2007, 06:01 AM   #7
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Quote:
Originally Posted by Mikko Lopponen View Post
It looks like it has been deinterlaced. What capture/editing software settings are you using? Do you happen to use FCP 6 with "no fields" in the settings? If so it is possible that it's deinterlacing the image.
I'm using:
HDV 1080p25 preset to capture
HDV 1080p25 (HD 1440x1080 / Field Dominance None) for a timeline.

The problem is that I can only see 'stairs' when objects are in front of a bright background. There are limited situations where stairs appears. Otherwise picture is good.
Exactly where I can find that "no fields" setting in FCP (or did you mean Field Dominance)?

Last edited by Poppe Johansson; September 11th, 2007 at 07:00 AM.
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Old September 11th, 2007, 09:03 AM   #8
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It has to do with the way Canon creates progressive frames from an interlaced ccd. The sampling means that alternate lines have 1/3 of colour information to build the picture from hence the stair stepping.

You'll only notice it on high contrast areas and has absolutely nothing to do with capture settings.
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Old September 11th, 2007, 09:53 AM   #9
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i konw this problem since my first test with that 25f mode...and i came to the
conclusion that i recieve better results when i film in 50i and use a good
deinterlacer afterwards(blending fields and move detection). hoped also to save those steps in my workflow...
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Old September 11th, 2007, 09:56 AM   #10
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So does the 24F have this problem or is it just PAL modes. It seems that all who have noticed this issue uses 25F-version of A1 ?
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Old September 12th, 2007, 02:51 PM   #11
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Originally Posted by Poppe Johansson View Post
I'm using:
HDV 1080p25 preset to capture
HDV 1080p25 (HD 1440x1080 / Field Dominance None) for a timeline.
Try setting field dominance to upper. I know it makes no sense, but FCP 6 WILL DEINTERLACE video material if field dominance is set to none. Then take another screen capture and show us the result.

FCP 5 did not do it and this has caused me many headaches. I don't want it to deinterlace, but I also don't want it to create interlacing in effects. It blows. I'm willing to bet that this will cure your problem. I've seen many images from the a1 that don't have any stairstepping artifacts and it shouldn't have them anyway!
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Old September 13th, 2007, 02:17 AM   #12
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Originally Posted by Mikko Lopponen View Post
Try setting field dominance to upper. I know it makes no sense, but FCP 6 WILL DEINTERLACE video material if field dominance is set to none. Then take another screen capture and show us the result. ...
I'm not a FCP guru, but isn't it impossible to choose upper field for capturing 25p(F) material via firewire? I think FCP forces you to 'none' field order if the preset is set 1080p25.
I tried to set upper field after capture, but it didn't change anything. Also it seems that stairs are already in the tape, though I can only check this via component out which forces me to use 1080i.
Are you sure about that "FCP6 will deinterlace", because the picture doesn't normally look like that. I'm quite sure that my captured material is 25p without any interlacing.
I have witness this stair effect in very few shots, so this could be the reason why you haven't seen this.

Still I'm wondering has anyone with NTSC 24F -version seen this happen?
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Old September 13th, 2007, 03:24 AM   #13
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Quote:
Originally Posted by Poppe Johansson View Post
I'm not a FCP guru, but isn't it impossible to choose upper field for capturing 25p(F) material via firewire? I think FCP forces you to 'none' field order if the preset is set 1080p25.
I had a 960x720 DVCPRO HD sequence and FCP deinterlaced it if field sequence was set to none. After capture, it doesn't do anything to the during capture. Maybe your FCP understands that those XH A1 files are progressive, but my FCP didn't understand my P2 files.

Quote:
I tried to set upper field after capture, but it didn't change anything.
Did you export an image and look at it? The preview window also deinterlaces if it's smaller than 100%. You could also try opening the files with quicktime and take a look at the direct stream.

Quote:
I have witness this stair effect in very few shots, so this could be the reason why you haven't seen this.
That's because 1440x540 is still enough resolution that you won't see those stairs everywhere. But they are there, just simpler to spot with high contrast edges.
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Old September 13th, 2007, 03:57 AM   #14
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I've done all that. Only step where deinterlacing could happen is capture, but I can't change those settings (1080p25 is field none like it should be). I can view material in Full HD scale (FCP and QuicktimePlayer), so what I see should be ok.
Here's the original clip you can download. It's very foggy shot with low light, but the 'stair effect' is really visible. Captured with 1080p25 preset.

Download clip here (25Mb):
http://aavekammari.pp.fi/stairs.mov
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Old September 13th, 2007, 11:23 AM   #15
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I can see the stair-stepping in 24f, to answer an earlier question. Not terrible, though, I find it to be very faint, only noticeable on contrasty edges, and if you go down to 1280x720, it's gone.
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