Monday, November 06, 2006

C.I.H. Explained

There is something special about going to a cinema to watch a film presented in CinemaScope. The curtains open to reveal a wall to wall screen with an image much wider than conventional home video's HDTV 1.78:1 can achieve.

Previously the best we could do at home was to letterbox that "Scope" image. Thanks to modern home theatre [digital] projectors combined with an anamorphic lens, it is possible to project all images at a Constant Image Height, recreating that DELUXE WIDE SCREEN cinema experience in the home and preserving the true Aspect Ratio the way the director intended and allow Home Theatre users to enjoy CinemaScope at home.

When set up correctly, a Constant Image Height system will allow you to switch between different Aspect Ratios. This may be done electronically using a video scaler [either in the projector or an external video processor] or by removing the lens from the light path for the smaller Aspect Ratios of 1.85:1/1.78:1 [second image] or 1.33:1 [third image]. There is only 4% difference between 1.85:1 and 1.78:1.


The C.I.H. system allows 100% of the projectors panel to display the "Scope" image at the full height of the screen with NO black bars top and bottom. Letter boxing only uses 75% of the vertical resolution for the image. The other 25% is wasted on the black bars to preserve the aspect ratio.

Standard Wide Screen like HDTV [1.78:1] and films with an aspect ratio of 1.85:1 will use the full height of the screen but the width will vary. The smaller image width is still very watchable because we are more sensitive to image height than image width.

1.33:1 IMAGE
Side pillars of unused screen will be seen when displaying smaller Aspect Ratios like the two images [1.78:1 and 1.33:1] above. Side masking may be employed to cover these areas of un-used screen to help create a more cinematic look.


Constant Image Height is a 2 part process - "Scaling and Optics". Here is how it works.

When a film's Aspect Ratio is "wider" than that of the display, the image height is reduced to fit in the width and still be able to maintain correct geometry. Normal "letter boxed" images [like the one above] waste precious vertical pixels on the black bars seen at the top and bottom of the image. This image is actually window boxed to show how a 16:9 letter boxed image would look when being projected onto a "Scope" screen.

PART ONE is the scaling or electronic reformatting of the image to use the full panel of the projector. The key to scaling for C.I.H. is to maintain the full width of image, but remove the black bars. As a result, the geometry is changed, making the image appear "tall and thin" as if "vertically stretched".

Full panel use has the potential to increase both the brightness and vertical resolution of the projected image. This can be done either with the projector [depending on the type of connection and source feed] or with an out board video processor. A 16:9 "enhanced" DVD is actually stored this way on the disc [in a 4 x 3 frame] so a "2.35:1" film will still have some black bars top and bottom that need to be removed. Blu-ray Disc offers 1920 x 1080 pixels and because they are not anamorphic, still contain black bars for Scope films.


PART TWO is the optical stretching of the image to restore the image geometry. The anamorphic lens sits in the light path of the projector and optically stretches the light beam by a factor of 33% (1.33x for video and 2x for film) in the horizontal direction. This takes the 1.78:1 ratio or 16:9 display and Horizontally Expands it by 1.33:1x resulting in an image with an aspect ratio of 2.37:1. This process therefore restores the geometry of the electronically "scaled" image, resulting in a full height, but now much wider "scope" image.


Subtitles, [whilst not in every film], are often needed for us to understand what is being said [particularly in a foreign film] when the spoken language is not our native language like in this scene from D-WARS. Both shots are taken with the image scaled for CIH using the Letterbox mode on the projector. As can be seen in the 1st shot, only the first line of text remains after Scaling for CIH. The 2nd line of subtitles have been removed along with the black bars during the Scaling process.


To solve this problem, I now use a Phillips [BDP3000] Blu-ray Player because it is one of the select few BD players capable of shifting sub-titles for BD and DVD. DVD subtitles are generally stored as a bitmap which Blu-ray players seem to shift vertically by about 10% anyway.


In my opinion, video transfers should not be altered from what was seen at the cinema. The subtitles should remain in the active image where they appeared in the cinema release. Theatrically most subtitles will be a single line of text that extends across the width of the screen.



The RUNCO CINEWIDE is probably the most expensive CIH solution, but is a total system comprising of everthing you need for CIH in your home including the purpose built DLP projector... If you already have a projector, there are quite a few anamorphic lens products on the market, some costing more than a projector itself. The prices range from just a few hundred to many thousands of dollars. There are basically two types - cylindrical [top image] and prismatic. The benefits of a cylindrical lens over a prismatic lens is that the cylindrical lens features adjustable optics allowing both horizontal and vertical lines to be brought into focus at the same time. Prismatic Lenses can not do this as their optics are fixed and not adjustable.


In May 2011, I upgraded the MK4 to MK5 as the new cylindrcial lens to my line of products.

When the projector is fed a "scaled" signal from an anamorphically (16:9) enhanced DVD or Scaled Blu-ray Disc and projected through the lens on to a "Scope" screen, it produces a DELUXE WIDE SCREEN presentation with NO black bars top and bottom...


When the LENS is properly aligned, the circles of this pattern should all appear "round" and you will have uniform focus from edge to edge.


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