Television system with provisions for displaying an auxiliary image of variable size

In order to selectively reduce the size of an auxiliary image, such as may be displayed within main image during a so called "picture-in-picture" or "PIP" mode of operation of a television system, a fixed amount of the auxiliary image is caused to be cropped from the auxiliary image without changing the compression ratio of the compressed auxiliary video signal from which the auxiliary image is derived.

FIELD OF THE INVENTION 
The invention concerns a television system with provisions for displaying 
an auxiliary image together with a main image, and more particularly with 
such provisions that are capable of changing the size of the auxiliary 
image. 
BACKGROUND OF THE INVENTION 
Many modern television systems include provisions for displaying an 
auxiliary image corresponding to an auxiliary video signal source as well 
as a main image corresponding to a main video signal source. Such 
provisions allow a viewer to monitor one program while watching another 
program. The auxiliary image may be displayed within the main image in a 
so called "picture-in-picture" or "PIP" format. The auxiliary image may 
also be displayed next to the main image in a so called 
"picture-outside-picture" or "POP" format. 
The auxiliary image is formed by converting the analog video signal from 
the auxiliary signal source to a digital video signal, "subsampling" the 
digital video signal by eliminating pixel samples and lines from the 
digital video signal, storing the resulting compressed digital video 
signal in a memory, and retrieving the stored digital from the memory in 
synchronism with the horizontal and vertical synchronizing components of 
the video signal from the main video signal source. A so-called 
"antialiasing" filter is utilized to reduce the bandwidth of the digital 
signal before compression to avoid artifacts in the auxiliary image due to 
the subsampling process. The digital signal retrieved from the memory is 
converted to an analog video signal and the resultant analog video signal 
corresponding to the auxiliary image is combined with the analog signal 
corresponding to the main image to form a combined analog video signal. 
The combined analog video signal is coupled to a display device. The 
combining operation is performed by a switching section or "multiplexer" 
which selectively decouples the main video signal from the display device 
and instead couples the auxiliary video signal to the display device 
during predetermined portions of predetermined horizontal scanning lines 
of the main video signal. 
The auxiliary image is usually considerably smaller than the main image. 
For example, the auxiliary image may be one-third the size of the main 
image. However, it may be desirable to be able to selectively reduce the 
size of the auxiliary image still further, for example, from one-third 
size to one-fourth size, so that the auxiliary image does not obscure the 
main image. One way of accomplishing this is to change the compression 
ratio of the auxiliary image. However, this requires relatively extensive 
and complicated circuitry for changing the subsampling ratio and the 
associated anti-aliasing filtering, and changing the management of the 
memory for storing of the subsampled digital signal. Moreover, the 
additional compression tends to make details of the auxiliary image and 
text and graphics inserted within the auxiliary image harder to see. 
SUMMARY OF THE INVENTION 
In accordance with the invention, in order to selectively reduce the size 
of an auxiliary image, a fixed amount of the auxiliary image is caused to 
be cropped from the auxiliary image without changing the compression ratio 
of the compressed auxiliary video signal from which the auxiliary image is 
derived.

DETAILED DESCRIPTION OF AN EMBODIMENT OF THE INVENTION 
FIG. 1A shows screen of a typical 4 by 3 aspect ratio television receiver 
with a relatively small auxiliary image corresponding to a video 
compression ratio 1/3 inserted within a full size main image during a PIP 
mode of operation. The 1/3 size auxiliary image tends to obscure the main 
image. Therefore, it is desirable to be able for the user to selectively 
cause the size of the auxiliary image to be reduced, for example, to a 1/4 
size auxiliary image. FIG. 1B indicates what occurs if the size reduction 
is accomplished by increasing the video compression ratio to 1/4. While 
more of the main image is made visible, the auxiliary image has been 
compressed to the point at which details in the auxiliary image are less 
visible. In addition, any text or graphics which has been inserted in the 
auxiliary image at the studio, such as closed caption text, or text which 
has been inserted in the receiver itself, such as channel numbers, becomes 
significantly less visible. 
In accordance with the invention, the size reduction of the auxiliary image 
is produced by cropping a predetermined portion of the original auxiliary 
image without changing the video compression ratio. The result is 
indicated in FIG. 1A by the 1/4 size auxiliary image labeled "1/4 
cropped". More of the main image is visible because of the size reduction. 
While some of the auxiliary image has been lost, image details and text or 
graphics are still relatively visible because the image has not been 
compressed. 
In addition, the circuitry required to reduce the size of an auxiliary 
image when the cropping method is employed is far less complicated than 
that required when the compression method is employed. The latter requires 
a considerable amount of complicated circuitry for changing the 
compression subsampling ratio and the associated anti-aliasing filtering, 
and the management of the memory for storing of the subsampled digital 
signal. The structural aspects of the invention will now be described with 
reference to FIG. 2. 
Briefly, in the PIP processing section of the television system shown in 
FIG. 2, a composite video signal corresponding to the auxiliary image, 
containing a luminance component and a chrominance component, is processed 
to form baseband components, such as a luminance signal and two color 
difference signals or three color difference signals. Each component 
signal is compressed, synchronized with the video signal corresponding to 
the main image and combined with a corresponding component of the main 
video signal to form a combined component signal. The combined component 
signals are coupled to a display device, such a picture tube. Since the 
PIP processing channels for the various components are similar, at least 
with respect to the present invention, only one PIP processing channel is 
shown in FIG. 2. In the following description, the terms "auxiliary video 
signal" and "main video signal" correspond to one of the component 
signals. 
As is shown in FIG. 2, the analog auxiliary video signal received at an 
input terminal 1 is converted to a digital video signal by a 
digital-to-analog converter 3. The digital auxiliary video signal is 
subsampled in a compression unit 5 to remove a predetermined number of 
lines and predetermined number of pixels per line. Compression unit 5 
includes an anti-aliasing filter for reducing the bandwidth of the 
auxiliary video signal prior to subsampling to reduce artifacts in the 
reproduced auxiliary image due to the subsampling process. The compressed 
auxiliary video signal is stored in ("written-into") a memory also 
included in compression unit 5 and retrieved from ("read-out") of the 
memory in synchronism with the vertical and horizontal synchronization 
components of the main video signal. The digital video signal which has 
been read-out of the memory of compressor 5 is coupled to a digital 
multiplexer ("MUX") or switch 7. The function of multiplexer 7 and an 
associated "border" unit 9 will be described below. For the moment, assume 
that multiplexer 7 couples the digital video signal which has been 
read-out of the memory to a digital-to-analog converter 11. 
Digital-to-analog converter 11 converts the digital video signal into an 
analog signal. The resultant compressed auxiliary analog signal is 
combined with the main analog video signal, which is received at a 
terminal 13, by an analog multiplexer or switch 15. The resultant combined 
video signal is coupled to a display device 17, where a picture including 
an auxiliary image within a main image is displayed. 
A clock unit 19 generates clock signal for various portions of the PIP 
processing section and a control unit 21 generates various control signals 
for the PIP processing unit. Control unit 21 is responsive to horizontal 
(H) and vertical (V) synchronization components of the main video signal 
and to user initiated PIP and CROP command signals. The PIP command signal 
initiates the PIP operating mode. The CROP command signal initiates the 
cropping operation by which the size of the auxiliary image is reduced. 
Multiplexer 15 is operated in response to a switching control signal to 
replace the main video signal with the compressed auxiliary signal at the 
desired location of the auxiliary image. Multiplexer 15 may be called an 
"overlay switch" because it combines the compressed auxiliary video signal 
and the main video signals (even though it replaces one signal with the 
other). The switching control signal for multiplexer 15 may be called a 
"fast switching" or "FSW" control signal because of the speed at which 
multiplexer 15 operates. 
More specifically, multiplexer 15 is operated to replace the main video 
signal with the auxiliary video signal during a predetermined portion of 
each field, starting at predetermined horizontal line corresponding to the 
top edge of the auxiliary image and ending at another predetermined line 
corresponding to the bottom edge of the auxiliary image, and during a 
predetermined portion of each horizontal scanning line within the 
predetermined portion of each field, starting with a predetermined pixel 
corresponding to the location of the left edge of the auxiliary image and 
ending with another predetermined pixel corresponding to the location of 
the right edge of the auxiliary image. This operation is indicated in FIG. 
4. The contents of the memory of compression unit 5 are read-out during 
the time intervals in which the main video signal is being replaced with 
the auxiliary video signal in response to address signals. 
Multiplexer 7 and associated "border" unit 9 and provide a border for the 
auxiliary image. Border unit 9 is a register which stores a digital value 
corresponding the shade of the border in the case of the luminance signal 
component, and a color level in the case of the color components. If only 
a gray-scale border is desired, the digital border values for the color 
components may correspond to blanking level. Multiplexer 7 is operated in 
response to a switching control signal to decouple the output signal of 
compressor unit 5 from digital-to-analog converter 11 and replace it with 
the digital border value at the desired location of the border. 
Multiplexer 7 serves to combine the compressed auxiliary video signal with 
a signal representing its border. Accordingly, multiplexer 7 may be called 
a "border insert" switch and its switching control signal may be called a 
"BORDER INSERT" switching control signal. 
More specifically with regard to the generation of the border, during a 
predetermined number (e.g., three) of horizontal lines above the top edge 
of the auxiliary image, border insert multiplexer 7 is caused to couple 
the border value provided by border unit 9 to digital-to-analog converter 
11 for a predetermined portion of each of the lines corresponding to the 
width of the auxiliary image plus the widths (e.g., three pixels) of the 
left and right sides of the border. This causes the top side of the border 
to be formed. During each of the predetermined number of horizontal lines 
corresponding to the height of the auxiliary image, border insert 
multiplexer 7 is caused to couple the border value to the 
digital-to-analog converter 11 for a predetermined number of pixels, e.g., 
three, before the left edge of the auxiliary image and after the right 
edge. This causes the left and right sides of the border to be formed, as 
is indicated in FIG. 4. Finally, during a predetermined number (e.g., 
three) of horizontal lines after the bottom edge of the auxiliary image, 
border insert multiplexer 7 is caused to couple the border value to the 
digital-to-analog converter 11 for a predetermined portion of each of the 
lines corresponding to the width of the auxiliary image plus the width 
(e.g., 3 pixels) of the left and right sides of the borders. This causes 
the bottom side of the border to be formed. 
It should now be understood that "overlay" multiplexer 15 actually serves 
to combine the compressed auxiliary video signal plus the border signal 
with the main video signal. With reference to FIG. 4, note that the 
duration of the high logic level of the FSW control signal for a 
horizontal line during which the auxiliary image is being displayed 
actually corresponds to the width of the auxiliary image plus the widths 
of the left and right sides of the border. Accordingly, the BORDER INSERT 
switching control signal is generated in association with the FSW control 
signal. 
The operation of the PIP processing section to selectively reduce the size 
of the auxiliary image by cropping a predetermined portion of the 
auxiliary image will now be described with reference to FIG. 3. FIG. 3 
shows an auxiliary image of a predetermined size, for example, 1/3 size, 
containing a circle, by way of example. To reduce the size of the 
auxiliary image, for example from 1/3 size to 1/4 size, the auxiliary 
image is cropped by removing approximately 12.5% of the auxiliary image 
from both of the left and right sides and both of the top and bottom. This 
means that an object (e.g. the circle) contained in the auxiliary image 
has the same size and location for both the 1/3 size and 1/4 size 
auxiliary images, although less of the auxiliary image is shown. 
The cropping is accomplished by controlling the overlay multiplexer 15 to 
remove an additional number of lines and an additional number of pixels 
per line from the compressed auxiliary signal. The compressed auxiliary 
signal is not changed and continues to be generated as in the 1/3 size 
mode. Viewed another way multiplexer 15 is caused to reduce the time that 
the compressed auxiliary signal is coupled to display unit 15 instead of 
the main video signal by changing the duration of the high logic level of 
the FSW control signal to extend over a time interval corresponding to the 
region of the auxiliary image which is to be cropped, as is shown in FIG. 
4. There is a corresponding change of the BORDER INSERT switching control 
signal so that the border is inserted in the correct location relative to 
the cropped auxiliary image, as is also shown in FIG. 4. 
Thus, in the exemplary embodiment, the use of the cropping method for 
reducing the size of the auxiliary image only involves changing two 
signals. No other signal need be changed. Moreover, in a PIP processing 
section in which border is not provided, the cropping method only involves 
changing one signal, the FSW control signal. This method of operation 
avoids the need for extensive and complicated circuitry because very 
little is changed in the system in order to accomplish the size reduction. 
FIG. 5 shows circuitry for changing the FSW and BORDER INSERT switching 
control signals for cropping the auxiliary image. Basically, the contents 
of registers which determine positions of the left and right edges and the 
top and bottom edges of the auxiliary image are selectively changed in 
response to the user initiated CROP signal. More specifically, digital 
words, e.g., including 8 bits, representing the positions of the left, 
right, top and bottom edges for the two auxiliary image sizes, e.g., 1/3 
and 1/4, are coupled to respective inputs of four digital multiplexers 
21-1, 21-3, 21-5 and 21-7. For example, in FIG. 5, "HP" represents the 
position of the left edge of the uncropped 1/3 size auxiliary image and 
"VP" represents the position of the top edge of the uncropped 1/3 size 
auxiliary image. Multiplexers 21-1 and 21-3 select the digital values for 
the positions of the left and right edges, respectively, and multiplexers 
21-5 and 21-7 select the digital values for the positions of the top and 
bottom edges, respectively. The outputs of multiplexers 21-1, 21-3, 21-5 
and 21-7 are coupled to respective registers 21-9, 21-11, 21-13 and 21-15. 
The contents of registers 21-9 and 21-11 represent the positions of the 
left and right edges of the auxiliary image and therefore also relate to 
the left and right sides of the border. The contents of registers 21-13 
and 21-15 represent the positions of the top and bottom edges of the 
auxiliary image and therefore also relate to the top and bottom sides of 
the border. A switching control signal generation unit includes pixel and 
line counters responsive to the vertical (V) and horizontal (H) 
synchronization components of the main video signal and a clock signal, 
and comparators for comparing the contents of registers 21-9 and 21-11 to 
the pixel count and the content of registers 21-13 and 21-15 to the line 
count to generate the FSW control signal. The BORDER INSERT switching 
control signal is generated in a similar way. 
In operation, when the uncropped 1/3 size auxiliary image is desired, the 
CROP control signals is caused to have a low logic level and the digital 
values representing the positions for left, right, top and bottom edges 
for the uncropped image are selected and coupled respective ones of 
registers 21-9, 21-11, 21-13 and 21-15. When the cropped 1/4 size 
auxiliary image is desired, the CROP control signals is caused to have a 
high logic level and the digital values representing the positions of the 
left, right, top and bottom edges for the cropped image are selected and 
coupled respective ones of registers 21-9, 21-11, 21-13 and 21-15. 
While the present invention has been described in terms of a specific 
embodiment, modifications may occur to those skilled in the art. For 
example, the not all of the four edge positions needs to be changed to 
reduce the size of the auxiliary image. This is less desirable in some 
respects than the specifically disclosed method. If the position of only 
one edge is changed, the aspect ratio will be changed. If positions of two 
orthogonal edges is changed, the center of the auxiliary image will be 
changed. In addition the topology may be modified. For example, an analog 
level corresponding to the border may be inserted after the compressed 
auxiliary signal is converted to analog form. These and other 
modifications are considered to be within the scope of the invention 
defined by the following claims.