# Why CIH Scaling Works



## Mark Techer (Jan 17, 2008)

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


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## Prof. (Oct 20, 2006)

Good info. Mark..:T


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## Blaser (Aug 28, 2006)

Mark Techer said:


> 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.
> 
> ...


Thank you for bringing 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...


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## Prof. (Oct 20, 2006)

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...


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## Mark Techer (Jan 17, 2008)

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


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## Vern Dias (Oct 31, 2008)

> 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..


Thats why a complete CIH setup always includes an external scaler or an HTPC, rather than depending on the projector to do the vertical stretch....

Vern


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## Prof. (Oct 20, 2006)

Good to have you on board Vern...
I'm sure your input on this forum will be much appreciated..


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## tbase1 (Nov 10, 2006)

I could not agree with you guys more. I have prismasonic V1000 with a Sanyo Z4 ,and a Key Digital HDMI scaler switch. Before I had my scaler all I had to do is rotate the prisms to go from 1.85 to 2.35. All was good , but I got fed up with doing that ,so in comes the scaler. Now I set the lens to passthrough for 2.35 with the scaler set to full ,and when I want to view 1.85 content I just go from full to letter box on the scaler. I have no distortion and no headaches with rotating lenses. I tried the cheap mans version of CIH/CIW ,but saw to much distortion.


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## John Simpson (May 10, 2007)

Hi guys,

Me again, back after a long stretch in the wilderness (well, downtown Hobart at least). Mark, it's great to see you've made your presence so well known with these guys -- have you given up your day job yet to just make Aussiemorphics?

To throw my coins in the fountain, I'm a bit jaded about full-time anamorphic since watching that bizarre Dark Knight blu-ray. I sense a re-occurring theme since a lot of blockbusters are now being released at Imax. Is it another case of "we have to compromise to satisfy the lowest common denominator"?

As for my progress on the new house, planning application for a more modest home has just gone into Council after ditching "Wychwood" (the wife and I split up sadly)... but no way am I giving up my dedicated HT room!

Cheers,
John


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## Blaser (Aug 28, 2006)

Indeed movies like dark knight are not friends with CIH:bigsmile:
Hopefully they are very seldom.


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## Prof. (Oct 20, 2006)

John Simpson said:


> As for my progress on the new house, planning application for a more modest home has just gone into Council after ditching "Wychwood" (the wife and I split up sadly)... but no way am I giving up my dedicated HT room!
> 
> Cheers,
> John


Hi John,

Sorry to hear that Wychwood is not going ahead..and of your separation..
Hopefully you'll finish up with a nice theatre out of all this..


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## Bruce Fisher (Nov 24, 2007)

Blaser said:


> Indeed movies like dark knight are not friends with CIH:bigsmile:
> Hopefully they are very seldom.


I don't have a CIH setup yet - still in construction (getting close though). I haven't heard/seen... why was Dark Knight not CIH friendly? What did they do to it?


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## Prof. (Oct 20, 2006)

Bruce,

I think what Blaser is talking about is that the AR changes from 2.40 to 1.78:1 briefly during the Blu-ray version of "The Dark Knight"..
I believe this also happens with some other discs as well..
Why or for what reason..I have no idea..:dunno:


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## John Simpson (May 10, 2007)

It's a result of the film being shown in Imax format: there are some landscape shots (for example, the scene of Gotham at night) that the director thought would be best to show without letterbox bars, to give the illusion of "full screen". So you'll find the presentation jumps between 2.4 and 1.78, depending on what's on screen.

Not good for a CIH setup, as you're seeing less than you're supposed to (ie: the top and bottom are cropped)!


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## Blaser (Aug 28, 2006)

Yes Prof! That's exactly what I meant :T


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## Prof. (Oct 20, 2006)

John Simpson said:


> It's a result of the film being shown in Imax format: there are some landscape shots (for example, the scene of Gotham at night) that the director thought would be best to show without letterbox bars, to give the illusion of "full screen". So you'll find the presentation jumps between 2.4 and 1.78, depending on what's on screen.
> 
> Not good for a CIH setup, as you're seeing less than you're supposed to (ie: the top and bottom are cropped)!


Great idea!!..for 16:9 projection or TV's..but not for us CIH guys..
Again,another example of catering for the mass market..

I have a copy of that movie on DVD and didn't notice any AR change..Is it only the Blu-ray version that does this?


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## John Simpson (May 10, 2007)

Prof. said:


> Is it only the Blu-ray version that does this?


Yeah, must be. In a way, it's a brilliant idea... imagine a 16:9 screen setup which suddenly loses the top and bottom black bars to show an enormous vista (no, not the software). But it's definitely no friend to CIH.


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## Blaser (Aug 28, 2006)

It sure does this on BD... :yes:


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## Prof. (Oct 20, 2006)

I'm still going to get that movie on Blu-ray though..
After seeing a good quality Blu-ray movie on my new HD projector and Blu-ray player just recently..I don't think I could ever buy another DVD!!..WOW!! Absolutely FANTASTIC image on my CIH..
Couldn't believe it could be SOOO!! much better..:unbelievable: :yay2:


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## Mark Techer (Jan 17, 2008)

Rather than start a new thread, i thought I would just add it to this one.

To keep it really simple, lets assume the 1920 x 1080 format is used and refer to the image at the bottom of the post.

* OK so Bottom Left is the original image and is what the final projected image will also look like.
* Top Left is the image letter boxed on video (BD) to fit within the 1920 x 1080 pixels. The actual image is now some 1920 x 810 pixels with the remaining 270 wasted on black bars.
* Moving on to the Top Right, when the image is Scaled for CIH (Vertical Stretch) it is remapped as if to fit a 1920 x 1440 display. Because our HD displays are 1920 x 1080, the top and bottom sections can not be displayed. They are cut off and there goes the black bars. The image now looks like the one at Bottom Right.
* After optical expansion from an anamorphic lens, the image now looks like the Bottom Left.


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