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What is Anamorphic?
In the television industry "Anamorphic" is the process of converting an original movie theater motion picture format (Wide Screen) to be viewed on a standard 4:3 screen. Most movies today use the 1.85:1 ratio or larger and the standard TV screen is 1.33:1 (4:3). Another way to look at anamorphic is the process of displaying a 16:9 (1.78:1) image on a 4:3 (1.33:1) display. "Anamorphic mode" or 16:9 mode as it is sometimes called, is accomplished by reducing the wide screen format to fit between the sides of the 4:3 display. To maintain the 16:9 aspect ratio of wide screen format, vertical size is reduced creating black bars at the top and bottom of the screen much like the common letterbox image. The difference between letterbox and anamorphic is that with letterbox much of the vertical resolution is lost in the black bars. In the graphics at the bottom, anamorphic mode (Left) shows all 540 vertical lines where letterbox (Right) only 360 lines are visible. The rest are used to create black bars. Notice that in the letterbox image the field of view is also reduced. Through use of the anamorphic process, the "wide screen" image will be displayed with little to no loss of the image on the 4:3 screen. Anamorphic mode should not be used on a picture that is already formatted for standard TV viewing (4:3). Doing so will distort the image. Anamorphic should only be used to view a signal formatted for 16:9. What this means is by using anamorphic mode a movie will be displayed on a standard 4:3 TV the way the director originally intended it to be displayed, provided it wasn't originally formatted for TV (4:3).
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Motion Picture Formats Compared to Standard TV and HDTV Formats
To review a bit of cinema and television history, most movies were and are filmed in what is referred to as "wide-screen" format. The Movie Industry uses this format because wide screen is closer to the human eyes' width and height perception. There are many so-called "wide-screen" formats currently in use by the Movie industry. Among the more popular are: 1.85 and 2.35; however, older movies were filmed in many screen ratios including: 1.33, 1.17, 1.375, 1.66, 1.75, 2.21, 2.40, 2.55, 2.59, and 2.76 (These ratios are more correctly written as "1.85:1...etc") Both standard NTSC and SDTV are 1.33:1 (4:3) with High Definition ATSC (16:9) at 1.78:1. Normal US movie screen standards have more or less settled on 1.85:1. There is little to no loss of picture information when converting the most common movie format, 1.85:1 to the HDTV format of 16:9 (1.78:1).
Diode Modulator
The diode modulator is used to correct the inner pin distortion associated with the flat faceplate of true flat tubes. Op-amp U24401provides gain and filtering for the WIDTH_REF line from the deflection SIP. This signal is comprised of a vertical rate parabola riding on a DC level that drives the pin output circuit. C24434 is the S-cap during the top and bottom of the vertical raster. At the very center, the effective value of the S-cap is the series combination of C24423 and C24418. This series combination causes the equivalent value of the S-cap to be less in the middle stretching the raster gradually as the vertical scan approaches the center and gradually decreases as it approaches the end of vertical scan. Because the S-CAP is floating above ground, a "bath tub" shape waveform is required for optimum performance and dynamic focus voltage waveform to maintain a constant peak-to-peak voltage. It is also required that the waveform be phase locked to the horizontal deflection. An interlock provides protection for the horizontal output transistor by routing ground from the Power Supply Deflection (PSD) board through J24401-3 to the deflection SIP. Without this ground, horizontal drive is defeated. T24401 and C24420 form a tuned circuit at twice the scan rate or 4H to give second harmonic correction. R24427, R24428, CR24405, CR24406, and C24419 form a "mouthtooth" damping circuit across the S-Cap. U24402 is used as an error amplifier and a filter. Its output is a DC voltage that is used to drive R24404. This DC voltage is switched to ground by Q24402 at a horizontal frequency. This generates a rectangular voltage waveform that is phase locked to the horizontal frequency. C24422 acts as a phase delay that is used to center the dynamic focus waveform. This rectangular voltage waveform is then buffered by U24402. This buffer also provides constant drive impedance for the double