MULTI-FORMAT DISPLAY DEVICE

Abstract: A multi-format display device such as a cathode ray tube (CRT) for displaying 4x3 and 16x9 formats has an aspect ratio such that the vertical dark bands which accompany the 4x3 format have about the same thickness as the horizontal dark bands which accompany the 16x9 format, whereby the obtrusiveness of the dark bands is minimized, and the image distortion is minimized when the images are stretched to fill the viewing area.

Description: Multi-format display device This invention relates to a display device for color television, and more particularly relates to such a display device capable of displaying more than one format of television signal. Cathode Ray Tubes (CRTs) for color television are generally designed to display the standard television format having a 4x3 aspect ratio, ie, the ratio of the width to the height of the display image is 4:3. Recently, there has been interest in displaying television images in the wider aspect ratio of 16x9, corresponding to the wide screen cinema format. Displaying such wide screen images on a conventional CRT results in large horizontal dark bands above and below the image, creating the impression that the image is contained in an elongated slot, and leading to the term "letterbox" for such displays. CRTs have been designed specifically to display the 16x9 format. However, since it is anticipated that television programming will include content in both the 4x3 and the 16x9 formats for the foreseeable future, a CRT capable of displaying both formats should appeal to a larger segment of the market. One design for such a multi-format CRT is disclosed in English Abstract 6- 275213 of Japanese Published Application No. 5-82705. This CRT has an aspect ratio (width-to-height) of 20: 13, which results in approximately equal areas of the 4x3 and 16x9 formats displayed. The horizontal dark bands which occur when the 16x9 format is displayed are significantly narrower than those which occur in the "letterbox" display. However, these horizontal dark bands are also significantly narrower than the vertical dark bands which occur when the 4x3 format is displayed. Such unequal dark bands are noticeable to the viewer when switching between programs having different formats. Moreover, such unequal bands make it more difficult for the television set manufacturer to design electronic stetching of the displays to minimize or eliminate the bands without distorting the image. In accordance with the invention, a multi-format display device is provided having a viewing area with an aspect ratio of approximately 13.4x9 to 13.5x9, which results in vertical and horizontal dark bands of approximately equal thickness when displaying the 4x3 and 16x9 formats, respectively. In accordance with another aspect of the invention, a multi-format display device is provided for displaying 4x3 and 16x9 formats centered in the viewing area in a manner to result in vertical dark bands of approximately equal thickness in the case of the 4x3 format and horizontal dark bands of approximately equal thickness in the case of the 16x9 format, the viewing area having an aspect ratio which results in vertical and horizontal dark bands of approximately equal thicknesses when displaying the 4x3 and 16x9 formats, respectively. The term "thickness" as used herein means the shortest dimension, ie, the height in the case of the horizontal bands and the width in the case of the vertical bands. Such dark bands of equal thickness minimize the overall obtrusive impact of the black bars when viewers switch between different formats. In addition, such dark bands of equal thickness minimize image distortion when the images are stretched to reduce or eliminate the dark bands. Moreover, such equal bands facilitate the design of electronic stretching means to stretch the 16x9 signals vertically and the 4x3 signals horizontally to reduce or eliminate the dark bands. Figs. 1(a) and 1(b) show a multi-format CRT display of the prior art, displaying a 16x9 format and a 4x3 format, respectively; Figs. 2(a) and 2(b) show a multi-format display of the invention, displaying a 16x9 format and a 4x3 format, respectively. Figure 1(a) shows a multi-format CRT display 10 of the prior art having a width w and a height h, and an aspect ratio w:h of 13.86:9. A 16x9 format image 12 has a width equal to w and a height equal to h - 2Ht, where Ht is the thickness of the dark horizontal bands 14 and 16. Figure 1(b) shows the same multi-format CRT display 10 having a 4x3 format image 17 with a height equal to h and a width equal to w - 2Vt, where Vt is the thickness of the dark vertical bands 18 and 19. In comparing Figs. 1(a) and 1(b), it is readily apparent that Vt > Ht by a substantial amount. Figure 2(a) shows a multi-format display 20 of the invention having a width w and a height h, and an aspect ratio w:h of 13.44:9. A 16x9 format image 22 has a width equal to w and a height equal to h - 2Ht, where Ht is the thickness of the dark horizontal bands 24 and 26. Figure 2(b) shows the same multi-format display 20 having a 4x3 format image 27 with a height equal to h and a width equal to w - 2Vt, where Vt is the thickness of the dark vertical bands 28 and 29. In comparing Figs. 2(a) and 2(b), it is readily apparent that Vt and Ht are very nearly equal. This not only results in a less distracting appearance as a viewer switches from one format to the other, but it also minimizes the amount of image stretch needed to reduce the size of the bands or to eliminate the bands entirely, so as to fill the viewing area entirely. Such minimal stretch results in minimal image distortion. In addition, dark bands of equal thickness greatly facilitate the design of the image-stretching circuitry. In practice, the values Vt and Ht may vary as much as plus or minus 10% from the condition Vt = Ht, while still retaining the above advantages. In the following table, an exemplary multi-format CRT display of the invention (equal bands) having a nominal diagonal measurement of 32 inches is compared to a multi-format CRT of the prior art (equal areas) having the same nominal diagonal measurement. '32" Multi Format Tube Picture Dimensions in inches The equal bars example of the invention may be calculated using the following equations: (w - 2Vt)/h = 4/3 (1) w/(h - 2Ht) = 16/9 (2) Vt = Ht (3) Setting the value of h = 9, the value of w = 13.44. While the invention has been described mainly in terms of CRT displays, it applies to any display type capable of displaying video information, including liquid crystal displays, plasma displays, plasma activated liquid crystal displays, foil displays and field emission displays.

Claims: CLAIMS: 1. A multi-format display (20) device having a viewing area with an aspect ratio of approximately 13.4:9 to 13.5:9. 2. The multi-format display device of claim 1 in which the aspect ratio is 13.44:9. 3. A multi-format display device (20) for displaying 4x3 and 16x9 formats centered in the viewing area in a manner to result in vertical dark bands of approximately equal thickness in the case of the 4x3 format and horizontal dark bands of approximately equal thickness in the case of the 16x9 format, the viewing area having an aspect ratio which results in vertical and horizontal dark bands of approximately equal thicknesses when displaying the 4x3 and 16x9 formats, respectively. 4. The multi-format display device of claim 3 in which the thicknesses of the vertical dark bands are within ± ten percent of the thicknesses of the horizontal dark bands.

Inventors: JOHNSON JEFFREY L, JOHNSON, JEFFREY, L.
Applicants: KONINKL PHILIPS ELECTRONICS NV, KONINKLIJKE PHILIPS ELECTRONICS N.V.
Application year: 2000
Main classification: H04N5
IPC codes: G09G5, H04N5