Flicker at bottom when using 16:9 mode (sample picture) at DVinfo.net

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Old October 26th, 2003, 10:55 PM   #1
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Flicker at bottom when using 16:9 mode (sample picture)

Greetings,
when I'm shooting with 16:9 mode, I get a a line at the bottom that keeps flickering. here's a picture:

http://www.nawaf.com/misc/interlaced.jpg

the flicker shows either with or without letterbox. it will NOT show when shooting in 4:3 mode. So I'm getting a feeling it's because of the cropping.

if I Deinterlace the video, it will go away. but what if I don't want a deinterlaced video ?!

right now, i'm getting away with the problem by cropping 7 pixels from the bottom.

The Camera is PAL XL1s, shooting on Normal mode (I didn't try Frame mode yet).

your help is appreciated.
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Old October 28th, 2003, 03:21 PM   #2
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I think you have to live with this. Since the edge of the picture/black matte in 16:9 mode is a perfect horizontal line, just by the way interlacing works, you are going to get some flicker at edges such as that one.

If you are in the US, i've heard also of flicker problems due to the PAL 50Hz frequency and the 60Hz lights, so try looking at it on an LCD screen, and see if the flicker is really there or just an artifact of interlacing.

Juan
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Old October 29th, 2003, 01:57 PM   #3
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I believe Juan is correct about this being completely attributed to interlaced video.

I've added letterboxes to footage in post and actually CREATED this flicker on the edge of the black matte! The solution I used was to actually deinterlace ONLY the letterbox - the flickering horizontal line then vanishes! The interlaced video underneath remains however.

So a solution to your problem would be to create your own 16:9 letterbox to match your camera letterbox size in Photoshop or Paint, then add it in post but be sure to select the deinterlace properties for it. In Adobe Premiere you just import the still image of the letterbox you made, add it to the timeline, then right click the letterbox and select field options -> deinterlace.

I hope this made sense. It works extremely well. If you give me the exact size in pixels I can make the letterbox for you, or try this one from my site www.starcentral.ca/letterbox.bmp

Dennis,
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Old October 29th, 2003, 02:44 PM   #4
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You may want to search this topic. It was a very hot topic here a year ago. Just search by number of views and you'll find it.
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Old October 29th, 2003, 11:02 PM   #5
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thanx for the reply guys.

Dennis,
I have the Matrox RTX100 card. I use the built-in letterbox, which does everything in real time.
anyways, the problem happens even before adding the letterbox, but i'll try your method.
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Old October 30th, 2003, 09:55 AM   #6
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Nawaf,

By the way, the letterbox bitmap I provided is 720 x 576 (PAL) but the actual frame (white portion) is 720 x 405 pixels - 85 pixel top bar, 86 pixel bottom bar.

When I applied my letterbox to your interlace.jpg I noticed too much of the image was being hidden so I created a new letterbox www.starcentral.ca/images/pal-letterbox75.bmp which fits your image much better. It has a 75 pixel bar top and bottom.

Hope this helps.

Dennis,
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Old October 30th, 2003, 08:40 PM   #7
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According to calculations by Rob Lohman for PAL 16:9 the bars would be 72 pixels. and for 1.85 widescreen 81 pixels bars, and 2.35 widescreen is 125 pixels. Thats on PAL. NTSC ones are slightly smaller for obvious reasons.

You can download masks in GIF format or use his calculator at: http://www.geocities.com/robvisuar/calc.htm.

I've used Rob's frames for ages, since he told us all here in DVinfo about his site and I have never had any problems. According to what I see when I have used them they seem spot on to me.

Sorry if I stole ur thunder Rob.....LOL
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