Cropping and resizing?

[killerteengohan]

The original video source has 8 pixels wide black bars on both the left and the right. 4:3 aspect ratio.

I wish to crop these off so the black bars on the left and right are gone.

I have cropped off the black bars, should I just leave the size at 624x480 because its MOD16 as well or should I stretch it to 640x480?

I wish to keep the original aspect ratio and video looking good but I remember being told by other encoders in forums, used to tell me to stretch it to fit 640x480 because I cropped and didnt resize it so I had a wierd lik 634x480 resolution or something close to it. (NOTE: My video was 4:3 aspect ratio and I only cropped off about 2-4 black lines from each side at most when they told me that) I left it in my opinion perfect because I didnt like to stretch the image. But pro encoders said I should stretch it to fit the 640x480 and that I probly wouldnt even notice the very small stretch.

So what size should I go with?

[manono]

That 'very small stretch' is what makes the aspect ratio 'normal' again. 720x480 is 1.5:1. Your video is supposed to be played at 1.33:1. At 720x480 things are slightly 'fat' and 'flat'. If you can find something round in the video you'll see. A moon or ball will be slightly 'flattened' at 720x480, or 704x480 after cropping. It has to be resized to play with the correct aspect ratio. You have 2 choices. One is to do the resizing yourself in the script, like to 640x480, 512x384, 480x360, etc, after cropping away the black bars. The other is to encode at 720x480 or 704x480 and set a PAR flag telling the player to resize it. Not all players will respect that flag, though.

[killerteengohan]

That 'very small stretch' is what makes the aspect ratio 'normal' again. 720x480 is 1.5:1. Your video is supposed to be played at 1.33:1. At 720x480 things are slightly 'fat' and 'flat'. If you can find something round in the video you'll see. A moon or ball will be slightly 'flattened' at 720x480, or 704x480 after cropping. It has to be resized to play with the correct aspect ratio. You have 2 choices. One is to do the resizing yourself in the script, like to 640x480, 512x384, 480x360, etc, after cropping away the black bars. The other is to encode at 720x480 or 704x480 and set a PAR flag telling the player to resize it. Not all players will respect that flag, though.

Make it normal again? If I crop off the black bars and leave it, it looks the same as if the black bars were on it during playback only the bars are gone.

I should still encode at 640x480 and make the image a bit wider to fill in where the black bars were?

I thought the way it was playing with the black bars on the side was normal and all I was doing was removing them.

[manono]

Make it 'normal' by resizing to 640x480.

And once again, 720x480 or 704x480 after removing the black bars isn't the correct aspect ratio. That's what 4:3 for DVD means. It tells the player how it's to be resized. 16:9 tells it to resize it a different way. Here, read this:

http://www.doom9.org/aspectratios.htm

[killerteengohan]

Make it 'normal' by resizing to 640x480.

And once again, 720x480 or 704x480 after removing the black bars isn't the correct aspect ratio. That's what 4:3 for DVD means. It tells the player how it's to be resized. 16:9 tells it to resize it a different way. Here, read this:

http://www.doom9.org/aspectratios.htm

I read it but Im only a little bit confused. I get it for the most part, but Im not using a widescreen dvd so I dunno if it applies as well. Ill take your advice and assume it does.

So is the top one the better one or the bottom one?? Which would you consider more the proper aspect ratio?

TOP = Cropped bars off with no resize 624x480.

BOTTOM = Cropped bars off with resize to 640x480.





I thought the top looked better and so did a friend of mine, but I wanna be sure. Thanks for the help

also Im only using this for playback on the PC, I dont plan on burning this if that changes anything.

[edDV]

The 8 black side pixels usually result from capturing broadcast video at 720x480 rather than native 704x480. The black pixels are actually captured 0 IRE blanking. The inner 704x480 contains the correct 4:3 or 16:9 aspect broadcast image. If one desires to convert 4:3 source to square pixels, the correct procedure is to first side crop 720 to 704 and then resize 704x480 to 640x480.

If instead you rescaled 720 to 640, the resulting frame is somewhat horizontally squeezed with ~7 pixel side bars (8*640/720=7.11). To restore aspect ratio, one would crop 7 pixels off each side and rescale the remaining 626x480 to 640x480.

NTSC capture


Note that the side bars are not 7.5 IRE black but blacker than black 0 IRE blanking. After capture, black is at digital level 16, blanking is at digital level 0 and white is at digital level 235.

[manono]

The top one wasn't just cropped with no resize. If that were the case it would be 704x480. It's 624x480.

The bottom one is correct.

[killerteengohan]

The top one wasn't just cropped with no resize. If that were the case it would be 704x480. It's 624x480.

The bottom one is correct.

By no resize, I meant I didnt resize it to 640x480 afterwards.

The top one was resized to 640x480 and then cropped the bars off.

[killerteengohan]

Thanks you 2 just saved me from making a big mistake.

[killerteengohan]

The 8 black side pixels usually result from capturing broadcast video at 720x480 rather than native 704x480. The black pixels are actually captured 0 IRE blanking. The inner 704x480 contains the correct 4:3 or 16:9 aspect broadcast image. If one desires to convert 4:3 source to square pixels, the correct procedure is to first side crop 720 to 704 and then resize 704x480 to 640x480.

If instead you rescaled 720 to 640, the resulting frame is somewhat horizontally squeezed with ~7 pixel side bars (8*640/720=7.11). To restore aspect ratio, one would crop 7 pixels off each side and rescale the remaining 626x480 to 640x480.


[Attachment 8117 - Click to enlarge]

So if I needed to crop 10 off of each side instead of 8 because of dot crawl or something would it be best to stretch it to 640x480 and thats it, or would it be better to cut 2 pixels off of the top and 2 off of the bottom to make it 4 extra off the sides and 4 off the top to match? or should I leave the height alone regardless?

[edDV]

The 8 black side pixels usually result from capturing broadcast video at 720x480 rather than native 704x480. The black pixels are actually captured 0 IRE blanking. The inner 704x480 contains the correct 4:3 or 16:9 aspect broadcast image. If one desires to convert 4:3 source to square pixels, the correct procedure is to first side crop 720 to 704 and then resize 704x480 to 640x480.

If instead you rescaled 720 to 640, the resulting frame is somewhat horizontally squeezed with ~7 pixel side bars (8*640/720=7.11). To restore aspect ratio, one would crop 7 pixels off each side and rescale the remaining 626x480 to 640x480.


[Attachment 8117 - Click to enlarge]

So if I needed to crop 10 off of each side instead of 8 because of dot crawl or something would it be best to stretch it to 640x480 and thats it, or would it be better to cut 2 pixels off of the top and 2 off of the bottom to make it 4 extra off the sides and 4 off the top to match?

More often you will find the captured video shifted a pixel or two to the right (e.g. 9 pixels left, 7 pixels right). If you did need to crop 10 each side for some reason, I'd just leave it as is (slightly narrower than 4:3). The active picture will be correct aspect ratio. Any vertical crop from 480 will cause display problems on TV sets (e.g. force a resize back to 480 introducing vertical resize artifacts).

[killerteengohan]

The 8 black side pixels usually result from capturing broadcast video at 720x480 rather than native 704x480. The black pixels are actually captured 0 IRE blanking. The inner 704x480 contains the correct 4:3 or 16:9 aspect broadcast image. If one desires to convert 4:3 source to square pixels, the correct procedure is to first side crop 720 to 704 and then resize 704x480 to 640x480.

If instead you rescaled 720 to 640, the resulting frame is somewhat horizontally squeezed with ~7 pixel side bars (8*640/720=7.11). To restore aspect ratio, one would crop 7 pixels off each side and rescale the remaining 626x480 to 640x480.


[Attachment 8117 - Click to enlarge]

So if I needed to crop 10 off of each side instead of 8 because of dot crawl or something would it be best to stretch it to 640x480 and thats it, or would it be better to cut 2 pixels off of the top and 2 off of the bottom to make it 4 extra off the sides and 4 off the top to match?

More often you will find the captured video shifted a pixel or two to the right (e.g. 9 pixels left, 7 pixels right). If you did need to crop 10 each side for some reason, I'd just leave it as is (slightly narrower than 4:3). The active picture will be correct aspect ratio. Any vertical crop from 480 will cause display problems on TV sets (e.g. force a resize back to 480 introducing vertical resize artifacts).

thats what I meant. when I crop the 2 off the top and bottom, I was gonna keep the size 480, I wasnt gonna leave it at 476. is that alright or should I just avoid cropping top and bottom period?

[edDV]

The 8 black side pixels usually result from capturing broadcast video at 720x480 rather than native 704x480. The black pixels are actually captured 0 IRE blanking. The inner 704x480 contains the correct 4:3 or 16:9 aspect broadcast image. If one desires to convert 4:3 source to square pixels, the correct procedure is to first side crop 720 to 704 and then resize 704x480 to 640x480.

If instead you rescaled 720 to 640, the resulting frame is somewhat horizontally squeezed with ~7 pixel side bars (8*640/720=7.11). To restore aspect ratio, one would crop 7 pixels off each side and rescale the remaining 626x480 to 640x480.


[Attachment 8117 - Click to enlarge]

So if I needed to crop 10 off of each side instead of 8 because of dot crawl or something would it be best to stretch it to 640x480 and thats it, or would it be better to cut 2 pixels off of the top and 2 off of the bottom to make it 4 extra off the sides and 4 off the top to match?

More often you will find the captured video shifted a pixel or two to the right (e.g. 9 pixels left, 7 pixels right). If you did need to crop 10 each side for some reason, I'd just leave it as is (slightly narrower than 4:3). The active picture will be correct aspect ratio. Any vertical crop from 480 will cause display problems on TV sets (e.g. force a resize back to 480 introducing vertical resize artifacts).

thats what I meant. when I crop the 2 off the top and bottom, I was gonna keep the size 480, I wasnt gonna leave it at 476. is that alright or should I just avoid cropping top and bottom period?

I see no value in the vertical crop. It would be similar to a slight letterbox on computer displays and hidden in overscan on TV sets.

Sometimes people overlay black to hide VHS head switch noise. Otherwise, I'd leave it 480.

[killerteengohan]

The 8 black side pixels usually result from capturing broadcast video at 720x480 rather than native 704x480. The black pixels are actually captured 0 IRE blanking. The inner 704x480 contains the correct 4:3 or 16:9 aspect broadcast image. If one desires to convert 4:3 source to square pixels, the correct procedure is to first side crop 720 to 704 and then resize 704x480 to 640x480.

If instead you rescaled 720 to 640, the resulting frame is somewhat horizontally squeezed with ~7 pixel side bars (8*640/720=7.11). To restore aspect ratio, one would crop 7 pixels off each side and rescale the remaining 626x480 to 640x480.


[Attachment 8117 - Click to enlarge]

So if I needed to crop 10 off of each side instead of 8 because of dot crawl or something would it be best to stretch it to 640x480 and thats it, or would it be better to cut 2 pixels off of the top and 2 off of the bottom to make it 4 extra off the sides and 4 off the top to match?

More often you will find the captured video shifted a pixel or two to the right (e.g. 9 pixels left, 7 pixels right). If you did need to crop 10 each side for some reason, I'd just leave it as is (slightly narrower than 4:3). The active picture will be correct aspect ratio. Any vertical crop from 480 will cause display problems on TV sets (e.g. force a resize back to 480 introducing vertical resize artifacts).

thats what I meant. when I crop the 2 off the top and bottom, I was gonna keep the size 480, I wasnt gonna leave it at 476. is that alright or should I just avoid cropping top and bottom period?

I see no value in the vertical crop. It would be similar to a slight letterbox on computer displays and hidden in overscan on TV sets.

Sometimes people overlay black to hide VHS head switch noise. Otherwise, I'd leave it 480.

Alrighty I got ya, thanks more than you know for the info. So dont crop vertically and if I do need to crop more than 8 off the left and right, dont bother and just leave it slightly narrower?

and if so, what if theres an annoying line where those extra 2 pixels are that I would like out of the video for pc playback? still leave it narrower?

[edDV]

The 8 black side pixels usually result from capturing broadcast video at 720x480 rather than native 704x480. The black pixels are actually captured 0 IRE blanking. The inner 704x480 contains the correct 4:3 or 16:9 aspect broadcast image. If one desires to convert 4:3 source to square pixels, the correct procedure is to first side crop 720 to 704 and then resize 704x480 to 640x480.

If instead you rescaled 720 to 640, the resulting frame is somewhat horizontally squeezed with ~7 pixel side bars (8*640/720=7.11). To restore aspect ratio, one would crop 7 pixels off each side and rescale the remaining 626x480 to 640x480.


[Attachment 8117 - Click to enlarge]

So if I needed to crop 10 off of each side instead of 8 because of dot crawl or something would it be best to stretch it to 640x480 and thats it, or would it be better to cut 2 pixels off of the top and 2 off of the bottom to make it 4 extra off the sides and 4 off the top to match?

More often you will find the captured video shifted a pixel or two to the right (e.g. 9 pixels left, 7 pixels right). If you did need to crop 10 each side for some reason, I'd just leave it as is (slightly narrower than 4:3). The active picture will be correct aspect ratio. Any vertical crop from 480 will cause display problems on TV sets (e.g. force a resize back to 480 introducing vertical resize artifacts).

thats what I meant. when I crop the 2 off the top and bottom, I was gonna keep the size 480, I wasnt gonna leave it at 476. is that alright or should I just avoid cropping top and bottom period?

I see no value in the vertical crop. It would be similar to a slight letterbox on computer displays and hidden in overscan on TV sets.

Sometimes people overlay black to hide VHS head switch noise. Otherwise, I'd leave it 480.

Alrighty I got ya, thanks more than you know for the info. So dont crop vertically and if I do need to crop more than 8 off the left and right, dont bother and just leave it slightly narrower?

and if so, what if theres an annoying line where those extra 2 pixels are that I would like out of the video for pc playback? still leave it narrower?

If you must h crop to say 700x480 then you can H resize to square pixel 638x480 and still keep the active picture near correct aspect ratio. The frame will just display slightly narrow on computer displays. The crop will be hidden in overscan on TV sets.

In the vertical direction, sometimes closed caption pulses show at the top and/or VHS head switch noise at the bottom. If you wish to hide these it is best to overlay black letterbox keeping 480 lines rather than crop or resize if TV display is important. If the file is only for computer display, you can crop to any frame size.