Vertical stretch source data?

[patchesj]

So here is my problem with the whole vertical stretch/lens vs zoom question... If your BR disc has 1080 lines output, and 270 of those are black pixels from the source you aren't really gaining any information (or loosing it for that matter) by stretching it and lensing it right?

It's like saying you take a CD, rip it to 256k MP3 and then re burn it as a regular CD. Your CD is back at full data rate, but you are just filling in the blanks with redundant information. You've lost (or never had in the case of BR 2.35:1 discs) the information you are displaying.

Sure the pixels might be .01" bigger with the zoom, but at least it's all the "real" content and not filled in with data the projector decides to put in there.

Am I missing the point??

Thanks.

[Prof.]

In reality you're losing 33% of your pixels in the black bar areas..

When the image is stretched vertically, the image is moved into the black bars top and bottom, thereby utilizing those lost pixels..
Then the image is stretched horizontally by the lens (as in a CIH system) again moving the image into the black bars..
So you're not back at square one, you've recovered all those lost pixels..

If you look at it from a viewing perspective..Before you would normally zoom the image, you have a small rectangular image on the screen with black bars all round...
The small image is very bright, contrasty with very good detail..
Now imagine that image looking just as bright and sharp, only now it fills the whole screen..That's what anamorphic projection does..

Unfortunately it's not quite that good, because you have now introduced additional optics into the light path, with some inherent limitations..CA and pincushion effect being the two most common..depending on the quality of the lens..and of course the quality of the optics..
But even with all that..the image seems takes on a quality that is quite different from just zooming..

One of the major downsides of zooming for most people is that you have to re-align the image each time you zoom from the standard 16:9 format..in some cases even having to refocus..
With anamorphic projection, that never happens..

[OvalNut]

Thank you Prof, that did it!

Finally, I get the WHY behind CIH anamorphic projection....

Thank you.


Tim

[patchesj]

I understand the 33% pixels unused argument. Perhaps it's just that I'm an audio purist trying to understand video. Let's look at this in a bandwidth perspective. A BR disc has 1080p24 streaming to your projector. That would be 25920 lines per second of data. If the disc is a 2.35:1 recording, there will be 6480 lines of black being transmitted per second and 19440 lines of "movie".

If you zoom, you are still seeing the entire 19440 lines as the director wanted.

If you stretch and lens, you are seeing the same 19440 lines plus 6480 lines of duplicate data.

I guess I don't see the importance of changing what the director decided was "the movie". How do you know they would have duplicated the same lines on the screen to "use all of the pixels"??

Until they start making native 2.35:1 projectors with 1080 lines by X number wide, and movies are produced and distributed in that format, we are stuck with whatever the least of two evils might be.

[Prof.]

OvalNut wrote:

Thank you Prof, that did it!

Finally, I get the WHY behind CIH anamorphic projection....

Thank you.


Tim

Your welcome Tim..

[patchesj]

If the argument for VS + lens is you are lighting up 25% more pixels on the LCD vs zooming so you'll have a brighter picture, then I get it. I still don't agree with the throwing away pixels, seeing more pixels/etc. statements. If the projector is duplicating pixels line over line to fill in the missing information, aren't you really just ending up with a double height pixel anyway? I don't see how you can throw away what you never had.

[Prof.]

patchesj wrote:

If the argument for VS + lens is you are lighting up 25% more pixels on the LCD vs zooming so you'll have a brighter picture, then I get it.

That's it exactly!..You aren't throwing away pixels, you're utilizing what was there originally..

With zooming you are pushing pixels off the screen, so instead of having the original 1080, you finish up with about 810!