Television – Synchronization – Sync generation
Patent
1992-10-23
1994-03-15
Groody, James J.
Television
Synchronization
Sync generation
348427, 348913, H04N 506, H04N 514, H04N 5262
Patent
active
052949834
DESCRIPTION:
BRIEF SUMMARY
The invention relates to the field of televisions having multiple picture displays for asynchronous video signals, and in particular, to such televisions having a wide display format ratio screen. Most televisions today have a format display ratio, horizontal width to vertical height, of 4:3. A wide format display ratio corresponds more closely to the display format ratio of movies, for example 16:9. The invention is applicable to both direct view televisions and projection televisions.
Televisions having a format display ratio of 4:3, often referred to as 4.times.3, are limited in the ways that single and multiple video signal sources can be displayed. Television signal transmissions of commercial broadcasters, except for experimental material, are broadcast with a 4.times.3 format display ratio. Many viewers find the 4.times.3 display format less pleasing than the wider format display ratio associated with the movies. Televisions with a wide format display ratio provide not only a more pleasing display, but are capable of displaying wide display format signal sources in a corresponding wide display format. Movies "look" like movies, not cropped or distorted versions thereof. The video source need not be cropped, either when converted from film to video, for example with a telecine device, or by processors in the television.
Televisions with a wide display format ratio are also suited to a wide variety of displays for both conventional and wide display format signals, as well as combinations thereof in multiple picture displays. However, the use of a wide display ratio screen entails numerous problems. Changing the display format ratios of multiple signal sources, developing consistent timing signals from asynchronous but simultaneously displayed sources, switching between multiple sources to generate multiple picture displays, and providing high resolution pictures from compressed data signals are general categories of such problems. Such problems are solved in a wide screen television according to this invention. A wide screen television according to the various aspects of this invention is capable of providing high resolution, single and multiple picture displays, from single and multiple asynchronous sources having similar or different format ratios, and with selectable display format ratios.
When an auxiliary picture is a small inset, various artifacts from imprecise synchronization with the main signal are tolerable. However, for some formats particularly suited for a wide screen television, such as two side by side pictures of equal size, such imprecision and artifacts cannot be tolerated. The large size of the auxiliary picture can make such artifacts painfully obvious. Generally, the video display and deflection system for composite picture displays is synchronized with the main video signal. The auxiliary video signal must be vertically synchronized with the main video signal and the video display. In a relatively inexpensive system, the auxiliary video signal can be delayed by a fraction of a field period in a field memory, and then speeded up in a line memory. In a relatively expensive and sophisticated system, such as is commonly used in broadcast quality studios, a four field synchronization system utilizes four dual port asynchronous field memories. Asynchronous memories, that is, those having independent write and read clock ports, are generally more expensive than synchronous memories.
According to inventive arrangements described herein, a degree of field synchronization can be achieved which substantially matches the performance of a four field system, but utilizes only a single synchronous video RAM as a field memory and a single asynchronous first in first out (FIFO) multiple line memory device. If the FIFO is a five line memory, the following artifacts can be encountered: (1) Two frame line shifts and 1 field line shift will occur each time the two signals precess through a video frame; and, (2) The auxiliary channel video gets scrambled at the bottom of the picture whenever the prec
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Canfield Barth A.
Ersoz Nataniel H.
Groody James J.
Herrmann Eric P.
Hsia Sherrie
Kurdyla Ronald H.
Thomson Consumer Electronics Inc.
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