Why CIH Scaling Works

[Mark Techer]

There has been some chat (on other forums) about scaling of the image for CIH when done in the projector. Without diving into the technical side of scaling, the so called "vertical stretch" works and can be proven with simple maths.

On Video, letterboxing is used to preserve the aspect ratio of the film. If the black bars of a CinemaScope film represent about 25% of the vertical rez, then the following works to all scaling for CIH.

1080 x 0.75 = 810. 810 x 1.3333333 = 1080. This once again gives us full vertical rez which we can then optically stretch to restore the geometry.

This actually works at all resolutions, and why CIH works for both HD and SD...

Mark

[Prof.]

Good info. Mark..

[Blaser]

Mark Techer wrote:

There has been some chat (on other forums) about scaling of the image for CIH when done in the projector. Without diving into the technical side of scaling, the so called "vertical stretch" works and can be proven with simple maths.

On Video, letterboxing is used to preserve the aspect ratio of the film. If the black bars of a CinemaScope film represent about 25% of the vertical rez, then the following works to all scaling for CIH.

1080 x 0.75 = 810. 810 x 1.3333333 = 1080. This once again gives us full vertical rez which we can then optically stretch to restore the geometry.

This actually works at all resolutions, and why CIH works for both HD and SD...

Mark

Thank you for gringing this out Mark! So what I understand is Black bars represent 25% of the whole screen, but they represent 33% of the 2.35 image.

What if the movie isnot 2.35:1, say like 2.2:1, I think this doesn't work anymore...

[Prof.]

Ahmed,

I think you'll find that the black bar percentages will differ slightly on some Cinemascope movies..In the case you mentioned, applying VS will move the image slightly above and below the borders, losing a bit of the image..This gets worse, the squarer the aspect ratio becomes..

Mark might like to just clarify that...

[Mark Techer]

When Top Gun was first released on DVD, it was presented as 2.20:1. The special edition is 2.35:1. When I bought Top Gun first time, I was presented with that exact issue.

So the choice was, do I watch window boxed, or do I clip a small portion from the top and bottom. I choose to do the second. When the new 235 version came out, it appears they too have simply cropped the top and bottom (expanding the black bars) as no -ones head is any more cropped on either version.

Thankfully, 2.20 is not common...

Mark