Correct cropping to achieve wider aspect ratios?

yukon33 · Member Joined: 05 Feb 2008 Location: United Kingdom

Of course this thread is an excellent in-depth guide to aspect ratios...

http://forum.videohelp.com/topic174200.html

...but since I am still a little green in this area and this is a bit overwhelming, could someone well versed in achieving different aspect ratios in NLEs advise me on the following?

> I am editing a film shot in 16:9 SD MiniDV, on a 16:9 timeline (in Avid Liquid). I am experimenting and want to apply black bars above and below my picture, to give the impression of an aspect ratio wider than 16:9. I am achieving this with a combination of cropping above and below, and also squeezing the picture slightly vertically (which I know will distort the picture and make everything look a bit 'wider', but I want this as a stylistic effect anyway).

My question is, to achieve the following correct aspect ratios, how many horizontal pixel lines from above and below the picture should I remove?

[1] 1.85:1 = ( 37:20 )
[2] 2.20:1 = ( 11:5 )
[3] 2.35:1 = ( 47:20 )

To experiment I am currently guessing it at around 1.85:1 and am pleased with the visual effect, but before I start cropping the whole film this way I thought I may as well find out what the correct pixel-removal amounts are.

Can someone supply the calculations, or explain in simple terms how to figure it out?

Thank you for any help

guns1inger · Posted: Jun 29, 2008 17:11

For

2.35 : 1 - crop to 720 x 336 (4:3), then resize 336 to 448 for 16:9. Assumes 4:3 source. If you have 16:9 source, just crop to 448 then pad to 576

2.20 : 1 - crop to 720 x 352 (4:3), then resize to 480 for 16:9. If you have 16:9 source, just crop to 480 then pad to 576

1.85 : 1 - crop to 720 x 432 (4:3) then resize up to 560 for 16:9. If you have 16:9 source then just crop to 560 and pad to 576.

All of these numbers assume PAL
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yukon33 · Member Joined: 05 Feb 2008 Location: United Kingdom

Thank you Gunslinger - but im still uncertain so just to clarify:-

720 is my screen width - this will not change, only height. By the way my 16:9 timeline properties are 720 x 576 [non-square].

So to achieve a picture size of 1.85:1, I shrink the height of the picture from 576 down to 432 pixels [and so-on for the other aspect ratio sizes I listed] based on the information in your reply?

Like I say I will achieve the black bars with a 2D Editor using a combination of 'height reduction' and 'cropping', and the final picture size is all I am concerned with, not the correction of the image [which will look like a slightly widened 16:9 picture].

So I just need to do the maths to work out how much to squeeze/crop in the 2D Editor to bring me down to 432 pixels high [1.85:1], 352 pixels high [2.20:1] or 336 pixels high [2.35:1]?

Thanks for any further clarification

jagabo · Member Joined: 09 Dec 2005 Location: none

You want to crop the height of the frame then restore it by adding black bars:

For a 720x576 16:9 source the remaining picture height should be:

height = 576 * 1.77777 / (desired AR)

So, to make it 2.35:1 you need a picture height of ~436 (576 * 1.77777 / 2.35). Crop a total of 140 (576-436) lines off the top and/or bottom (it doesn't necessarily have to be half and half). Then restore the frame by adding a total of 140 lines of black to the top and bottom (again, it doesn't necessarily have to be equal amounts).