Why CIH Scaling Works - Home Theater Forum and Systems - HomeTheaterShack.com

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post #1 of 20 Old 05-30-08, 08:26 AM Thread Starter
Mark Techer
 
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Why CIH Scaling Works

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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post #2 of 20 Old 05-30-08, 08:15 PM
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Re: Why CIH Scaling Works

Good info. Mark..

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post #3 of 20 Old 05-31-08, 11:13 AM
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Re: Why CIH Scaling Works

Quote:
Mark Techer wrote: View Post
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 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...

ASME AI
Yamaha RX-V2500, Wharfedale Diamond 9.6 Fronts, Wharfedale Diamond CM Center, Diamond DFS Surround and rear, Behringer FBQ 2496, Dual RL-P18s 625L LLTs, Dual TA-2400 Pro (2 * 2000 W Amp), Samsung HD870 DVD player, Carada BW 16:9 106" screen, Epson TW-2000, 60 Gb PS3
Important HT proverbs:
- "You can never have too much headroom" (talking about bass)
- "you can never have too big a screen" (talking about still pictures)


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post #4 of 20 Old 05-31-08, 07:50 PM
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Re: Why CIH Scaling Works

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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post #5 of 20 Old 06-02-08, 08:45 AM Thread Starter
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Re: Why CIH Scaling Works

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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post #6 of 20 Old 10-31-08, 09:22 PM
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Re: Why CIH Scaling Works

Quote:
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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post #7 of 20 Old 11-01-08, 05:56 PM
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Re: Why CIH Scaling Works

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

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post #8 of 20 Old 11-19-08, 08:15 PM
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Re: Why CIH Scaling Works

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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post #9 of 20 Old 06-22-09, 09:33 PM
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Re: Why CIH Scaling Works

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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post #10 of 20 Old 06-23-09, 02:22 AM
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Re: Why CIH Scaling Works

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

ASME AI
Yamaha RX-V2500, Wharfedale Diamond 9.6 Fronts, Wharfedale Diamond CM Center, Diamond DFS Surround and rear, Behringer FBQ 2496, Dual RL-P18s 625L LLTs, Dual TA-2400 Pro (2 * 2000 W Amp), Samsung HD870 DVD player, Carada BW 16:9 106" screen, Epson TW-2000, 60 Gb PS3
Important HT proverbs:
- "You can never have too much headroom" (talking about bass)
- "you can never have too big a screen" (talking about still pictures)


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