Television – Basic receiver with additional function – For magnification of part of image
Patent
1992-11-06
1994-02-08
Groody, James J.
Television
Basic receiver with additional function
For magnification of part of image
348594, 348595, H04N 3223, H04N 5262
Patent
active
052852822
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
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.
Almost all video products currently available to consumers have a format display ratio of 4.times.3, whereas the format display ratio of video production varies widely. If an aspect ratio greater than 4.times.3 is used for video production, an aspect ratio conversion must be performed before display on a consumer television or picture distortion will occur. One method of aspect ratio conversion is known as letterboxing. Letterboxing maintains more (or all) of the horizontal information, at the expense of the number of displayed lines in each field. A video source produced in the 16.times.9 format would contain 181 lines of video each field when converted to a 4.times.3 letterbox format. The extra lines that are not used in each field can be set to a flat field black (or gray) level. Higher aspect ratio sources would contain proportionally fewer lines per field.
SUMMARY OF THE INVENTION
A wide screen television, as described herein for example, can have a format display ratio of 16.times.9. This provides an opportunity to display signals in the letterbox format with greater flexibility. Letterbox signals that were originally produced in the 16.times.9 aspect ratio may be zoomed, that is expanded, vertically to fill the screen, with no loss of horizontal information or distortion. An automatic letterbox detector can be based on the assumption that the video signal will have no active video, that is, a substantially constant luminance value not higher than a threshold value. Alternatively, letterbox detection can be accomplished by calculating two gradients for each line in the video field. The first gradient, designated the positive gradient, is formed by subtracting the minimum valu
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Altmanshofer Robert D.
Cavazos Enrique R.
Fried Harvey D.
Groody James J.
Hsia Sherrie
Laks Joseph J.
Thomson Consumer Electronics Inc.
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