Television – Basic receiver with additional function – Multimode
Reexamination Certificate
1997-10-17
2001-03-27
Hsia, Sherrie (Department: 2614)
Television
Basic receiver with additional function
Multimode
C348S556000, C348S913000
Reexamination Certificate
active
06208385
ABSTRACT:
FIELD OF THE INVENTION
The present invention generally relates to a letterbox image detection apparatus for detecting a letterbox image signal.
The present invention relates to a letterbox image detection apparatus which is utilized in TV receivers having a wide aspect screen for detecting boundary position data of central main images and matte tops or bottoms of screen images, so as to block out the matte tops and bottoms from the display screen and thus to expand the main image on the whole display screen.
BACKGROUND OF THE INVENTION
In recent years, 16:9 wide aspect TV receivers have been widely in use to add realism of theater for audiences at home.
Recently, video softwares adapted for broadcast systems represented by wide-clear visions, VTRs, laser discs, etc. have been widely used.
EDTV-II type broadcasts are adapted for displaying on 16:9 aspect screens. While some of movies or the like recorded in laser discs and video tapes have a screen aspect wider than the 4:3 standard aspect screen as employed in the conventional TV receivers
These wide aspect programs are transmitted through a TV broadcast signal so-called letterbox image which is formed by a central image area (hereinafter referred to main image) and black belt-shape non-image areas which are disposed an the top and bottom of the main image. In such wide aspect TV receivers there are many ones which have functions of letterbox image detections, i.e., a function of detecting boundaries of the main images and the non-image areas and then blocking out the non-image areas from the display screen and thus expanding the main image both in the vertical and horizontal directions to display on the full screen of the TV receivers.
FIGS. 23
a
and
23
b
are an explanatory diagrams showing an image display for video softwares compatible with conventional wide aspect TV receivers. Wherein
FIG. 23
a
shows an image displayed on the 4:3 aspect screen. While
FIG. 23
b
shows the same image displayed on the 16:9 aspect screen.
In
FIGS. 23
a
and
23
b
, a video software compatible with a wide aspect TV receiver provides a black band (hereinafter referred to the non-image area) on the top and bottom of the central letterbox image to maintain a compatibility with the 4:3 aspect image from the viewpoint of relationship with the current 4:3 aspect image signal as shown in
FIG. 23
a.
Such picture is called a letterbox image. A wide aspect TV receiver has a function to detect a letterbox image and expand the picture in the vertical direction (called as a vertical expansion) so that the top and bottom non-image areas are not visible as shown in
FIG. 23
b
when such a letterbox image is provided.
FIGS. 24
a
and
24
b
are explanatory diagrams showing a conventional image display with a caption band superposed on the lower non-image area against a video software compatible with wide aspect TV receivers. Wherein
FIG. 24
a
shows an image displayed on the 4:3 aspect screen. While
FIG. 24
b
shows an image displayed on the 16:9 aspect screen.
As shown in
FIG. 24
a,
when an image with a caption band superposed on the lower non-image area is displayed on the 4:3 aspect screen, the caption band is displayed as it is, on the other hand, as shown in
FIG. 24
b,
when an image is displayed on the 16:9 aspect screen, the vertical expansion is made likewise but in order to prevent the caption band from becoming invisible, the image is expanded to the upper non-image area and the lower portion of the caption band.
To make this operation, most wide aspect TV receivers includes a letterbox image detector for detecting a letterbox image signal.
FIG. 25
is an explanatory diagram showing features of a letterbox image.
In
FIG. 25
, a first feature of the letterbox image is that there are the non-image areas on the top and bottom of the letterbox image.
A second feature is that the boundary of the non-image area and the picture area (hereinafter referred to the main image) is sharp and expands across one screen image.
A third feature is that there is the main image laterally expanding around the center of the screen.
When such the first through third features are all satisfied, the letterbox image detection apparatus determines that a picture is a letterbox image.
The letterbox image detection apparatus discriminates between a picture is a letterbox image and a normal aspect image by obtaining an average luminance level and an average chrominance level across one screen image for one screen and by considering an accumulation of that value for one screen. In general, a large accumulation for several fields or frames is performed for determining whether a small accumulation across only one field or frame has stably the feature of the letterbox image, the determination is made using. In the example shown in
FIG. 25
, an accumulation a
0
of an average luminance level and an average chrominance level satisfies all the conditions for the letterbox image and are stable over several pictures, it is determined to be a letterbox image and a microcomputer in a TV receiver is directed to perform the vertical expansion. Further, at the same time, when an accumulation of image signal of the aspect ratio 4:3 having a picture which is not a letterbox image, that is, having a picture in the non-image area (hereinafter referred to as a normal aspect image) is obtained, the letterbox image detection apparatus regards it as a normal aspect image and conveys the cancellation of the vertical expansion to the main microcomputer. If a picture cannot be determined to be a letterbox image or a normal aspect image, the picture is regarded as cannot be determined and the microcomputer is directed to maintain the current state.
FIG. 26
shows an example of a letterbox image containing a caption band.
In
FIG. 26
, in case of a picture which )as an edge at the lower side in the accumulation b
0
of an average luminance level and an average chrominance Level for one screen and further, the luminance sharply changes in the lower non-image area, the letterbox image detection apparatus detects it and conveys that the picture is a letterbox image having a caption band to the main microcomputer. At the same time, the picture start and end position data and the caption band end position data are conveyed to the main microcomputer.
FIGS. 27
a
and
27
b
are an explanatory diagrams showing an example or a first erroneous detection of a conventional letterbox image detection apparatus.
In
FIGS. 27
a
and
27
b
, a conventional letterbox image detection apparatus detects a letterbox image using an average luminance level and an average chrominance level across one screen image and therefore, when a scene changes, for instance, from a letterbox image to such a normal aspect image like the scene of the moon in a dark night as shown in
FIG. 27
a,
the average luminance and average chrominance levels detected by the letterbox image detection apparatus are always below a threshold of a normal aspect image and the level becomes not that of a normal aspect image nor a letterbox image. As a result, the letterbox image detection apparatus outputs a determining impossible signal. Here, an ordinary vertical expansion condition when the determining is impossible is to maintain the current state and therefore, in case of the display on the 16:9 aspect screen, if an image before the scene change was fling away by a letterbox image, the display on the screen remains unchanged and an image chipping occurs in the true display as shown in
FIG. 27
b.
FIGS. 28
a
and
28
b
are explanatory diagrams showing an example of a second erroneous detection of a conventional letterbox image detection apparatus.
In
FIGS. 28
a
and
28
b,
an example of an erroneous operation reverse to the operation in
FIGS. 27
a
and
27
b
is shown. As shown in
FIG. 28
a,
if a scene was changed from a normal aspect image (on a normal aspect display) of the scene of the moon in the dark night to a scene of the sun appearing at the center, the accumulation c
0
satisfies all of the features of the letterbox image at
Akamatsu Naoki
Konishi Kazuo
Satoh Kohichi
Hsia Sherrie
Kabushiki Kaisha Toshiba
Pillsbury & Winthrop
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