What everybody wants to know regarding cropping and resolution

[Ipod guru]

After sifting through the forum threads and reading many postings it becomes apparent that there is still widespread ambiguity regarding successful conversion of widescreen dvds. Seemingly like many others, im still searching for the right parameters to convert widescreen dvds with an aim of reducing the appearence those dreaded black bars during playback.

One option is to simply turn the "widescreen" option off in ur ipod settings menu. I DONT WANT TO DO THIS AS THIS OPTION IS A QUICK FIX WHICH CUTS OFF THE SIDES OF YOUR PICTURE.

So perhaps for the new users like myself, it would be INCREADIBLY useful for those (who have perhaps experimented previously and found good results) to offer a rough template for the two naturally recorded widescreen aspect ratios of 16:9 (1.83:1) and 16:9 (2.35:1).

First, lets take the 16:9 (1.83:1) aspect ratio:

1. Cropping Top and Bottom: Can anyone suggest a suitable amount of pixels to crop at top and bottom to fully remove the black bars hence saving file space? (I understand that when the ipod setting for "widescreen" is "ON" it may re-introduce its own black bars. My aim of cropping them off is soley to reduce file size in this context).

2. Cropping the Sides: Ive heard that cropping the sides SLIGHTLY, in conjuntion with re adjusting the picture size (via resolution settings), will help reduce the salience of the black bars. However if you crop too much im guessing you will be back to square one - (Loosing too much of the picture from either side - a similar consequence of disabling "widescreen" in your ipod settings).

3. The Resolution Settings: The default appears to be 320 by 240 and ive heard that this is approximately the "right" size for an ipod screen. However, will adjusting the height to a smaller setting help remove the black bars by either narrowing or stretching the picture. If so what is a good guide? 320 by 180? (I understand adjusting this TOO much will have a noticable effect on the screen proportions, thats why it appears to be a balancing act).

4. Finally, after doing all of this, the million dollar question is: Do you have the ipod widescreen setting turned on or off??

Now, lets take the 16:9 (2.35:1) aspect ratio and apply the same four questions outlined above...

If anyone is willing to offer any information to any of these four questions (WITH REFERENCE TO THEIR RELEVANT ASPECT RATIO, please specify which one) i would be most appreciative - champagne would fall from the heavens... On that note, thanks again to Sketch for helping me with my last essay....:rolleyes:

[Midiman]

First... 16:9 has nothing to do with 2.35:1. Both are mathmatical ratios. 16:9 is 16/9 = 1.78:1 (the standard for wide screen VIDEO... not film/movies). 4:3 is 4/3 = 1.33:1 (typical full screen television or old movies) 2.35:1 is CinemaScope, 2.85:1 is also popular... in theatrical terms. Both are wider or MUCH wider than typical 16:9. The equivilent of 2.35:1 expressed in the same the same format as 16:9 would be 37.6:9. 9 is the common denominator and expresses the height. 16 and 37.6 express the width in relation. You can see one is more than twice as wide as the other. More on this below.

Second... to many of us, the black bars are not "dreaded". They are necessary to display the entire picture in a properly proportioned picture. By all means, do away with them if you like losing 1/3 to 1/2 (or more) of the picture or you don't mind people looking freakishly tall and skinny.

To address some of your questions:

1) Cropping. If your video is from a DVD that has actually been letterboxed... which means the black bars are REALLY part of the signal, you should crop whatever is needed to remove them only because they take up extra bandwidth and filespace. This is a rare instance though. Most widescreen movies are anamorphic and the black bars are not in the picture. They are just displayed by your TV as blank space.

2) Cropping the sides. This is kind of a horrible thing to do. When a full screen version of a wide screen production is released, the process used is called pan and scan. It's called that because they use a 4:3 window over the original widescreen source... and they can slide it around... sometimes showing you what the left side of the film is... sometimes showing you the right side... and sometimes moving (panning) like a camera would between the two. This is necessary because many times a scene consists of two people facing each other (from the side) having a conversation. To simply lop off the left and right edges, you are left with a wonderful view of the empty room between them and most of the action... GONE!

3) Resolution: The iPod screen is 320x240. 4:3. 1.33. Full screen. The resolution you encode at depends, primarily, on two factors. First: what is the original aspect ratio of the source? Second: are you encoding to watch on the iPod screen or on a larger, external display? Here are some guidelines for some of the most common aspect ratios based on an assumption that you're watching them on the iPod:

4:3 or 1.33:1 - 320x240 (Full screen)
16:9 or 1.78:1) - 320x180 (Video wide screen standard)
1.85:1 - 320x172 (US and UK theatrical wide screen standard)
2.35:1 - 320x136 (CinemaScope/Panavision)
2.85:1 - 320x112 (Ultra Panavision)

One of the more interesting was Cinerama. It used 3, 4:3 projectors side by side... and therefore should have had a 3:1 aspect ratio... but once overlap and everything was taken into account, it came down to about 2.65. How the West Was Won was shot like this.

You want to see REALLY widescreen? Try Polyvision. It has a 4:1 aspect ratio. That would be 320x80!

In the case of the ratios expressed as X:X, the meaning is X units wide by X units tall. So 4:3 would have the same proportional size if it was 4" wide and 3" tall, or 4' wide and 3' tall or 400 pixels wide and 300 pixels tall. Same deal with 16:9. There are also many other ratios out there. 2.20 (The Sound of Music). 2.76 (Ben-Hur). In all cases, once you have established your target width (320 in the case of the iPod screen) dividing the width by the aspect ratio will yield the proper height. 320/2.35=136, 320/2.85=112, etc.

Further complicating these numbers is a requirement by most mpeg encoders that any height or width resolution should be evenly divisible by 16. This doesn't seem to be the case with the H.264 codec used by Videora and the iPod has no trouble playing files encoded with off axis numbers. An example might be in our height for 1.85 video above. 172/16=10.75. It's not evenly divisible. The closest LEGAL number would be 11x16=176. But, again, neither the H.264 codec or the iPod seem to care much about this. You might notice a line in the console that points it out and mentions that compression may be adversely affected... but I haven't found that to be the case.

In the interest of being semi complete in as far as what I've presented here, these are the resolution adjustments I would make to keep things MPEG legal (evenly divisible by 16)... IF I was going to make those adjustments. I probably wouldn't in THIS case. That's just me.

4:3 or 1.33:1 - 320x240 (Full screen)
16:9 or 1.78:1) - 320x176 (Video wide screen standard)
1.85:1 - 320x176 (US and UK theatrical wide screen standard)
2.35:1 - 320x144 (CinemaScope/Panavision)
2.85:1 - 320x112 (Ultra Panavision)

I have NO idea where you came up with 1.83:1....

Midiman: Television producer/director/editor/graphic artist/2D & 3D animator for PBS for 13 years.

[Sketch]

Midiman: Television producer/director/editor/graphic artist/2D & 3D animator for PBS for 13 years.
Holy street cred!!! Awesome. I am making additional (generally supportive) comments here.

Second... to many of us, the black bars are not "dreaded". They are necessary to display the entire picture in a properly proportioned picture. By all means, do away with them if you like losing 1/3 to 1/2 (or more) of the picture or you don't mind people looking freakishly tall and skinny.
I know I made this point in our last discussion, but I felt the need to emphasize that going from widescreen to fullscreen requires one of the two consequences. I understand losing the sides might be undesirable, but I don't see how a distorted picture is a better alternative.

1) Cropping. If your video is from a DVD that has actually been letterboxed... which means the black bars are REALLY part of the signal, you should crop whatever is needed to remove them only because they take up extra bandwidth and filespace.
And AFAIK there isn't a standard number of pixels that will work for every 1.85:1 NTSC DVD (as an example). If there were, I'm sure the lovely folks at Red Kawa would have incorporated that into these releases. Hence the ambuiguity.

Someone may suggest initial guidelines, but I use an AVISynth (http://avisynth.org/) plugin called AutoCrop (http://avisynth.org/warpenterprises/) to customize each DVD rip. From there I calculate the resized iPod video and possibly reset crop settings a little bit for a better aspect ratio match.

This is a rare instance though. Most widescreen movies are anamorphic and the black bars are not in the picture. They are just displayed by your TV as blank space.
Really? Most of my widescreen for films are letterboxed. I guess I'm just lucky.

Here are some guidelines for some of the most common aspect ratios based on an assumption that you're watching them on the iPod:

4:3 or 1.33:1 - 320x240 (Full screen)
16:9 or 1.78:1) - 320x180 (Video wide screen standard)
1.85:1 - 320x172 (US and UK theatrical wide screen standard)
2.35:1 - 320x136 (CinemaScope/Panavision)
2.85:1 - 320x112 (Ultra Panavision)

If you're watching them on both the iPod and using it for TV-Out, double each axis for 640 width.

Further complicating these numbers is a requirement by most mpeg encoders that any height or width resolution should be evenly divisible by 16. This doesn't seem to be the case with the H.264 codec used by Videora and the iPod has no trouble playing files encoded with off axis numbers... You might notice a line in the console that points it out and mentions that compression may be adversely affected... but I haven't found that to be the case.
I still do it anyway as it optimizes efficiency. The difference may not be noticeable, but I use these multiples as a force of habit. If the ratios don't match very well, I'll crop a bit (usually 8 pixels or fewer) on each side for a better match.

[Midiman]

I understand losing the sides might be undesirable, but I don't see how a distorted picture is a better alternative.

It's not. I was being facetious... again. You'll get used to me. When I look down the barrel of 007's gun, it had better be ROUND... not egg shaped!

[Sketch]

It's not. I was being facetious... again. You'll get used to me. When I look down the barrel of 007's gun, it had better be ROUND... not egg shaped!
No, I know you were being facetious, but I guess I'm not sure if black bars and pan'N'Scan aren't acceptable for iPodguru, I'm not sure what else is left.

[Midiman]

No, I know you were being facetious, but I guess I'm not sure if black bars and pan'N'Scan aren't acceptable for iPodguru, I'm not sure what else is left.


And just to be clear... pan & scan is NOT what he'll get if he simply crops. A static window on the center of a wide screen film is not what pan & scan is. But... those are the only three options.

1 - Live with the bars (see the whole movie properly)
2 - Crop the sides off (lose possibly critical picture information)
3 - Compress the sides in (make people tall and skinny, all circles will look like eggs)

[Sketch]

Thanks for the correction. Yeah, just taking the sides off wouldn't be this smar (http://en.wikipedia.org/wiki/Pan_and_Scan)t.

[Midiman]

That's brilliant! Everyone should make a point of clicking that link and taking a GOOD look at the pan & scan animation of Seven Brides for Seven Brothers. You'll be amazed at what you will lose by simply hacking off the sides of a movie.