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01-23-2020, 01:35 AM
WarbirdVideos WarbirdVideos is offline
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Question:

I have video that's 720 x 480. I then crop the frame to eliminate the head switching at the bottom of the frame and the black borders. So now the frame is 708 x 470 (pixels). I output the video at 720 x 480 which increases the size.

So the question is - how are the missing pixels added back in, or are they? Is there interpolation taking place? There must be some quality loss, but is it proportionate to the pixels that were removed during cropping?

Thanks,
Steve
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  #2  
01-23-2020, 01:43 AM
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lordsmurf lordsmurf is offline
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Interpolation? Probably depends on software.
VirtualDub = no
Avisynth = no
Pixels are simply truncated, if frame size not set to resize. (Noting in VirtualDub, you resize to a 720x480 palette -- not the palette contents, which just re-centers on the colored/black background palette.)

708 = 12 pixels chopped off sides.
12 are added back to mask for 720. Basic math. 708+12=720

IMPORTANT: ALWAYS CROP BY 2 WHEN INTERLACED! Never odd numbers!

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  #3  
01-24-2020, 01:06 PM
josem84 josem84 is offline
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You need to add black borders & re-center the frame after cropping. You will end up with your original 720x480 frame size. Doing it right, you'll keep the original AR intact and you won't degrade the image resizing it to something other than the original frame size.

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Originally Posted by WarbirdVideos View Post
I have video that's 720 x 480. I then crop the frame to eliminate the head switching at the bottom of the frame and the black borders. So now the frame is 708 x 470 (pixels). I output the video at 720 x 480 which increases the size. So the question is - how are the missing pixels added back in, or are they? Is there interpolation taking place? There must be some quality loss, but is it proportionate to the pixels that were removed during cropping?
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  #4  
01-24-2020, 03:40 PM
WarbirdVideos WarbirdVideos is offline
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So truncating views at a frame as an image rather than pixels?

Adding black borders back defeats the purpose of cropping them out. And if you render the video at the cropped settings (708x 472), quality suffers. I'm assuming that the frame size needs to be divisible by 16, and 708x 472 is not divisible by 16 - correct?
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  #5  
01-24-2020, 04:03 PM
josem84 josem84 is offline
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Quote:
Originally Posted by WarbirdVideos View Post
Adding black borders back defeats the purpose of cropping them out. And if you render the video at the cropped settings (708x 472), quality suffers. I'm assuming that the frame size needs to be divisible by 16, and 708x 472 is not divisible by 16 - correct?
Not at all... you're removing noise, which is the purpose of the cropping, and using solid black instead to fill the frame. You're safe with mod4 or larger.
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  #6  
01-24-2020, 05:33 PM
WarbirdVideos WarbirdVideos is offline
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Great - thanks guys!
Steve
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