Kodi DSPlayer – DirectShow Player for Windows
Constant Image Height vs. Constant Image Width vs. Constant Image Area Projection

Constant Image Height (CIH): A wide aspect ratio (2.35:1 to 2.4:1) CinemaScope screen is used to project a full 21:9 image. Standard 16:9 content fills the height of the screen, but not its sides, and CinemaScope content fills both the screen width and height. Either CinemaScope content is zoomed by the projector to fill the full scope screen space, or 16:9 content is shrunk by a video processor until it fits the screen height. Two-way screen masking is often moved into position for 16:9 videos to cover the blank left and right portions of the screen.

Constant Image Width (CIW): A standard 16:9 screen is used to project both 16:9 and 21:9 CinemaScope content. The width of the image remains the same, but the height is altered with CinemaScope content, which is cropped in height and framed by black bars. Two-way screen masking is used to cover the top and bottom of CinemaScope videos to hide the black bars. 

Constant Image Area (CIA): A non-standard screen size, typically 2.05:1 or wider, is used to project images of different sizes. Standard 16:9 content is zoomed to a size larger than a widescreen CinemaScope screen, but smaller than a regular 16:9 screen. CinemaScope 21:9 content is zoomed to a wider aspect ratio than a regular 16:9 screen, but slightly less wide than a 2.35:1 - 2.40:1 native CinemaScope screen. The center of the screen is filled with an image of similar size, but both the width and height change with each aspect ratio change. Four-way screen masking is used to hide the top, bottom, left and right borders of the image for all aspect ratios.

Anamorphic Lens: Replaces the zoom method of filling a CinemaScope aspect ratio by using a combination of a specialized anamorphic lens and a vertical or horizontal stretch function. CinemaScope content is stretched vertically (and sometimes horizontally) by the projector or a video processor to fill the height of a CinemaScope screen and an anamorphic lens pulls the image horizontally until it fills the screen width. So this set up is essentially the same visually as a Constant Image Height set up with the anamorphic lens typically being moved aside when 16:9 videos are played.

Each projection type relies on a different screen size to display all aspect ratios:


If you look at the comparison of screen sizes above, the height of the image is the same across each aspect ratio (:1), which reflects the same aspect ratios used by most common video sources, but the width differs. So choosing any of these aspect ratios as the default screen ratio involves trade-offs in both width and height when sources with different aspect ratios are rescaled for a projector screen that is wider or narrower than the source aspect ratio.

Pros and Cons of Each Projection Method

Constant Image Height (CIH): Creates the largest projected image for 21:9 CinemaScope content, but projects a smaller 16:9 image compared to a 16:9 screen.

Screen area is maximized when a widescreen CinemaScope movie is played:


Constant Image Width (CIW): Presents the largest projected image for 16:9 content, but loses size compared to a CinemaScope screen when projecting 21:9 content. Does not require a projector zoom lens or lens memories to resize CinemaScope videos to a larger size. 

Widescreen CinemaScope movies are presented with horizontal black bars:


Constant Image Area (CIA): Loses to both CIH and CIW when playing either 21:9 or 16:9 content. However, 16:9 movies are larger than when projected on CinemaScope screens and 21:9 content is larger than when projected on a 16:9 screen. So CIA provides the best balance for all formats. Considerable hassle can be involved in finding compatible zoom lenses and moving four-way masking in place for all aspect ratios.

Anamorphic Lens: Has the same pros and cons as CIH, but comes with some additional benefits. Unused panel space previously occupied by black bars is replaced by the addition of new pixels used by the vertical or horizontal stretch and a moderately brighter image is projected because the projector's entire light output is directed onto a smaller screen area. The cons include the high expense of the necessary anamorphic lens and some potential distortion of the image due to the effect of the anamorphic scaling. 

A Constant Image Height Refresher

Choosing the Right Aspect Ratio

Film Studies 101: A Beginner's Guide To Aspect Ratios

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