Aspect Ratios (1.33 -> 1.5, 1.78 -> 1.85) (1 Viewer)

[Brian Dobbs]

thanks for all of the tremendous help! So in actuality, computer playback must subtract lines of pixels to correctly display the image in it's correct aspect ratio? Does that mean I am going to miss those lines? What I mean is will it severely detract from the overall picture quality?

Why is there a difference in pixel dimension? A TV pixel is 1 pixel x .9 of a pixel, so that must mean the reference pixel is a computer monitor pixel?

This will take a little time to fully comprehend.

p.s. thanks for the link Nick

 

[MarkHastings]

So in actuality, computer playback must subtract lines of pixels to correctly display the image in it's correct aspect ratio? Does that mean I am going to miss those lines? What I mean is will it severely detract from the overall picture quality?

Another head scratcher...I'm not sure what a computer does to translate the 720 pixels into 648, but it's probably similar to the ways photo programs reduce pictures...the process is called "Interpolation"..instead of just throwing away a pixel and that's the end of it...it throws away the pixel and then takes the deleted pixel and blends it into the surrounding pixels, giving it a more softer edge.

 

[Nick_Scott]

I'm not sure what a computer does to translate the 720 pixels into 648, but it's probably similar to the ways photo programs reduce pictures

Most media players can do it a number of different ways depending on your processor speed, and the type of file.

Out of curiosity, I took a movie trailer that was 720x480 and RE-ENCODED it for 96 x 480 NTSC.

I was curious what Windows Media Player would do with a non-standard NTSC 4X3 format.

LOL- It still played in the proper 4x3 ration, but it converted the 96x480 to 96x90!
Thats alot of missing information!! The strange thing was the media-player "window" was 96x480, and would not let me shrink it. Strange...

OTOH, I popped it in my DVD player, and it played fine at 96x480. The 'pixels' were very, very wide.

 

[Dan Rudolph]

thanks for all of the tremendous help! So in actuality, computer playback must subtract lines of pixels to correctly display the image in it's correct aspect ratio? Does that mean I am going to miss those lines? What I mean is will it severely detract from the overall picture quality?

A computer isn't necessarily subtracting pixels. It may be adding. It depends what resolution it's displaying at. It isn't much different from how anamorphic video is saled down for a 4:3 display.

 

[MarkHastings]

A computer isn't necessarily subtracting pixels. It may be adding. It depends what resolution it's displaying at. It isn't much different from how anamorphic video is saled down for a 4:3 display.

That's an interesting thought. So, instead of taking the 720x480 and subtracting vertical lines to fit the 640x480 (4x3)...it might actually be adding horizontal lines to fit a 720x540 (4x3) area.

 

[Ken Chan]

Yeah; if your desktop is big enough, most DVD player programs will scale 16:9 up to 960x540, for example.

If your head hasn't exploded already, here's more about pixel aspect ratios than anyone should ever know.

//Ken

 

[Brian Dobbs]

If your head hasn't exploded already

lol

 

[MarkHastings]

Ken,

Thanks for that link. It explained (better than I did) why 486 lines of horizontal res. is used in video and not in DVD:

For starters, all the 525/59.94 equipment I have only works in 720×480, not in 720×486! How do you explain that?
525/59.94 video signal has 486 active (image-carrying) scanlines, but modern digital video equipment usually crops off 6 of them. Why? To get the height of the image down to 480 pixels, which is neatly divisible by 16.


Why is it important to have the height and width of the raster image divisible by 16?
Modern digital video applications such as DV, DVD and digital television (DVB, ATSC) often use MPEG-1 or MPEG-2 formats (or their derivatives) which are all based on 16×16 pixel macroblocks. Having the height and width of the image readily divisible by 16 makes it easier and more efficient for an MPEG encoder to compress video.