Quantcast Better to resize video or let player scale? - digitalFAQ Forum
  #1  
04-01-2015, 10:31 PM
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After cropping overscan, if I didn't want to mask, would it be better to resize SD video to a friendly resolution like 640x480 or is it better to crop and let the player resize the cropped video to screen resolution?
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  #2  
04-01-2015, 10:55 PM
sanlyn sanlyn is offline
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Why are you cropping "overscan"? What do you mean by "overscan"? Do you mean black borders or something like head switching noise across the bottom of the tape? Why are you resizing? Why not replace cropped borders with new black borders or just mask over the old ones and avoid incurring additional quality loss and changing the final aspect ratio of the image?

You can make your video 640x480 if you want, but what is the intended output format? Is it DVD? BluRay? AVCHD? 640x480 is invalid for those formats. Standard definition DVD/BD/AVCHD don't use square-pixel frames anyway. You must be talking about web or PC output at 4:3 for un-encoded or square-pixel formats. Otherwise, your question doesn't make sense. What aspect ratio do you want your players to use, and how will they know what you want?

General rule: video is neither rubber nor plastic. It's pixels, either square in shape or slightly rectangular. Pixels cannot be resized to make higher or wider frames; that's done by interpolating between small groups of old pixels and bigger groups of new pixels. There is no such thing as perfect or lossless resizing. So the rule is, don't ever resize unless you absolutely have to. If by resizing to "screen" resolution you mean resizing a 640x480 video to 1920x1080? I wouldn't dare, and it's the wrong aspect ratio for 4:3 video, and I'm prtty sue that it isn't what you meant. Maybe "screen resolution isn't really what you meant. Maybe you meant "display aspect ratio" ??.

Now, because we don't have much info about why you're cropping or by how much, then I could make some wild guesses. Say you cropped a 4:3 video so that's it's now 624x420. After you crop is it smaller than that? Or is it larger than 640x480? If you resize it to 640x480, then it's likely a 4:3 square pixel video,maybe like an mp4 for web use or something. It won'tbe BluRay or DVD for disc playback, so maybe this is for PC. web, hard drive, or video server playback? Or would it be 640x480 for straight square-pixel playback on a USB stick in your disc player?

Videos don't have overscan. Overscan is a factor in displays, not in videos.

Can you give us more detail? What video format are you working with? lossles AVI? Internet downlaod? VHS capture? What was the video's original frame size? If you left the video at its cropped size, what size would it be and how would a player know what "size" or "resolution" you're looking for?

Could keep on guessing, but usually I would not be so lazy and would just mask what was cut away in order to maintain the original image content's aspect ratio. If that sort of thing is of no importance to you, then resize -- because there's no player in the world that can play every possible or oddball video frame size correctly without special encoding flags or manual settings from you.

Mainly, most players and TV's are better at big-scale resizing than the software most of us have available.

Last edited by sanlyn; 04-01-2015 at 11:44 PM.
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04-01-2015, 11:04 PM
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Video is going to iPad/tablet viewing, so its going to be an x264 mp4, undecided as to whether to make anamorphic or square.

There is crap on the top and sides I want to get rid of to make it cleaner, videos are sourced from Betacam. Aspect ratio will be 4:3 if I resize or strange if I don't, but the crap needs to go for the best viewing experience in this case I think.
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04-01-2015, 11:07 PM
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iPad viewing needs MP4 (H.264) and progressive content. So you must deinterlace -- and hopefully with a good method (QTGMC).

Masking the overscan is usually the safest method. If you do crop, the crop must also be 4x3. In other words, you cannot cut off 10 pixels from each side, as that a 1x1 crop. Otherwise, you'll screw up the aspect ratio. Again, masking is simpler. Most viewers won't notice a mask, but they will notice if a person is too fat or too skinny. Or if a circle is oval.

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04-01-2015, 11:40 PM
sanlyn sanlyn is offline
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Precisely so. The original image aspect ratio and its relationship to the DAR and the pixel ratio (PAR) -- frequent victims of obsessive croppers and border haters.
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04-02-2015, 09:13 PM
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Quote:
Originally Posted by lordsmurf View Post
iPad viewing needs MP4 (H.264) and progressive content. So you must deinterlace -- and hopefully with a good method (QTGMC).

Masking the overscan is usually the safest method. If you do crop, the crop must also be 4x3. In other words, you cannot cut off 10 pixels from each side, as that a 1x1 crop. Otherwise, you'll screw up the aspect ratio. Again, masking is simpler. Most viewers won't notice a mask, but they will notice if a person is too fat or too skinny. Or if a circle is oval.
If I were going straight to DVD or Blu Ray, this is exactly what I would do. I wanted to crop as you describe according to the aspect ratio, but if I crop proportionally, should I be re-sizing back to the 640x480 source resolution or let the player do it?

Quote:
Originally Posted by Sanlyn
Precisely so. The original image aspect ratio and its relationship to the DAR and the pixel ratio (PAR) -- frequent victims of obsessive croppers and border haters.
I laughed out loud. I imagine I am one of these people, but if you were convert for example a DVD for a tablet, you would not crop?
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04-02-2015, 10:07 PM
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640x480 is a raw 4x3 resolution. (4x3 DAR, or display aspect ratio)

PAR = "picture/pixel aspect ratio", and is about as unhelpful as it gets. I never use this stupid term.

720x480 is 3x2 SAR (storage aspect ratio). But this does not matter. It's just extra information for now. I'm only showing how the typical "720x480" source resolution is to be ignored. When you talk about the image, cropping, etc, then the SAR doesn't matter. Forget about it. Pay attention to SAR only when decoding and encoding -- not for doing stuff between those two steps.

Nothing is 1x1. 1x1 is a cube. Video is never square. The problem come when people treat it as such. Again, 10px from each side messes up all aspect ratios, DAR, SAR, PAR, etc.

A proper 4x3 crop is 4 units wide, by 3 units vertical.

But the other issue is the new video is still going to be 640x480. So you must "zoom in". This creates another problem with the clarity of the content. It alters clean lines, giving a slight stair-step in the size change. So cropping is not *just* cropping, but anti-aliasing as well. You can also create halos (technical: ringing), and introduce chroma errors. Remember, the chroma is not 4:4:4 on your source, but probably 4:2:2 at best. Those new errors must also be filtered.

So ... are you sure you want to crop?

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04-02-2015, 10:18 PM
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Quote:
Originally Posted by lordsmurf View Post
640x480 is a raw 4x3 resolution. (4x3 DAR, or display aspect ratio)

PAR = "picture/pixel aspect ratio", and is about as unhelpful as it gets. I never use this stupid term.

720x480 is 3x2 SAR (storage aspect ratio). But this does not matter. It's just extra information for now. I'm only showing how the typical "720x480" source resolution is to be ignored. When you talk about the image, cropping, etc, then the SAR doesn't matter. Forget about it. Pay attention to SAR only when decoding and encoding -- not for doing stuff between those two steps.

Nothing is 1x1. 1x1 is a cube. Video is never square. The problem come when people treat it as such. Again, 10px from each side messes up all aspect ratios, DAR, SAR, PAR, etc.

A proper 4x3 crop is 4 units wide, by 3 units vertical.

But the other issue is the new video is still going to be 640x480. So you must "zoom in". This creates another problem with the clarity of the content. It alters clean lines, giving a slight stair-step in the size change. So cropping is not *just* cropping, but anti-aliasing as well. You can also create halos (technical: ringing), and introduce chroma errors. Remember, the chroma is not 4:4:4 on your source, but probably 4:2:2 at best. Those new errors must also be filtered.

So ... are you sure you want to crop?
Still looking into the idea of cropping, but wondering if resizing and encoding vs encoding and letting the player resize.

It seems like the options are generally accept it, hide it, or look at a significant drop in video quality by cropping/resizing.
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04-02-2015, 11:13 PM
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Accepting is really is not an option, as it hogs the bitrate. So a mask is best.

You cannot just crop and let it encode. Encoders and formats also require a certain block size. You can just take off 4x3, and let it alone. The encoder will crash, or refuse the source. The player may choke, as it expect a certain size. So the crop must be resized. And again, the resize introduces new artifacts.

As sanlyn said, obsessive croppers. Don't be that guy. Youtube already has too many as it is.

The only time that cropping is okay is when the video is accompanied by a downsize. For example, the torrent "scene" has HDTV source, with cropped overscan noise, then downsized to something like 640x360 or 720p. But VHS is already low resolution (comparatively), so you add more loss by upsizing for a crop.

Then again, it is a iPad. They may not notice. Anything under 13" tends to be too blurry to see much loss in detail. However, if you view it larger, it's obvious even to an untrained eye.

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