Method and apparatus for generating progressively scanned television information

A technique is disclosed for generating a progressively scanned video signal from an interlaced signal without the need for motion-adaptive processing. Low resolution information is obtained from the current interlaced field, and the remaining detail information is obtained from a stored signal that includes a prior field or fields. The obtained signal can then be displayed with progressive scanning at full resolution and without motion artifacts.

BACKGROUND OF THE INVENTION 
This invention relates to video signal processing and, more particularly, 
to an improved method and apparatus for generating a progressively scanned 
video signal. 
In recent years, television display systems capable of displaying larger 
numbers of lines than standard television, for example, 1125 lines per 
frame as compared to 525 lines per frame for NTSC television, have become 
more popular. However, in order to take advantage of this enhanced 
ability, not only should the display device have greater resolution 
capability, but the signal to be presented should be in a form to take 
full advantage of the display device's performance. 
Sometimes, a high definition video signal may be available for display. In 
other situations, a standard television signal (e.g. 525 lines per frame 
for NTSC) can be converted to a format for display with an increased 
number of lines per field, such as by using a line interpolation 
technique. 
It has been recognized that using a progressive display format has certain 
advantages over the standard (for example NTSC) interlaced display format. 
Compared with an interlaced display, a progressive display eliminates 
interline flicker, and reduces the visibility of the field-line structure 
that is noticeable when a viewer makes vertical eye movements. 
In systems where an interlaced video signal is converted to progressive 
format for display, as is done in certain high definition television 
systems, there has been a need to utilize motion-adaptive processing in an 
attempt to overcome problems inherent in the conversion. In particular, on 
the one hand, if information from a full frame (two successive interlaced 
fields) is combined in generating the progressively scanned frame, there 
will be motion artifacts that result from part of the information being 
from an "old" field. On the other hand, if only the current field 
information is used, the resulting image will have good motion rendition, 
but suffers a loss in vertical resolution, since only half the available 
lines are being used. A solution currently employed is to provide both 
types of information processing, and to also provide motion detection 
circuitry to control selection of which type of processing is to be used 
during a particular portion of the image to be displayed. In portions of 
the picture where there is little or no motion, information from the full 
frame (including the prior field) is combined, whereas when motion is 
detected, only information from the current field is utilized. It would be 
advantageous to be able to eliminate the need for motion-adaptive 
processing in these types of systems. 
As described in my U.S. Pat. Nos. 4,517,597, 4,628,344 and 4,652,909, and 
in my copending U.S. patent application Ser. No. 07/005,296, now U.S. Pat. 
No. 4,701,783, an electronic video signal (television signal) can be 
encoded at reduced bandwidth by lowering the frame refresh rate of the 
high spatial frequency components, while maintaining the frame refresh 
rate of at least a portion of the low spatial frequency components at the 
standard rate. If done in a specified manner, this will not cause 
substantial degradation in the ultimately displayed image, since human 
vision cannot perceive changes in high spatial resolution information at 
as fast a rate as it can perceive changes in low spatial resolution 
information. Accordingly, as has been previously set forth, an electronic 
video encoding and decoding system can be devised which takes advantage of 
this, and other, characteristics of human vision by encoding higher 
spatial resolution video components to be at a temporal information rate 
which approximately corresponds to the highest rate actually perceived by 
human vision for such components; thereby eliminating the need to encode 
these components at a higher rate, which inherently wastes bandwidth. 
Also, as shown in the prior patents and copending application, the low 
spatial resolution information can be generated in a form which is 
compatible with standard television video, e.g. NTSC video. 
It is among the objects of the present invention to provide an improved 
method and apparatus for generating a high definition video display in 
progressive scan format which utilizes signals that are in accordance with 
the system described in my referenced prior patents and application. It is 
also among the objects of the invention to provide a technique for 
generation of video in progressive scan format that has application to 
other types of high definition video systems, as well as to other video 
systems which would benefit from having a progressive scan format, 
regardless of their particular original number of lines or resolution 
capabilities. 
SUMMARY OF THE INVENTION 
Applicant has discovered that a progressively scanned video signal can be 
successfully obtained from an interlaced video signal without the need for 
motion-adaptive processing. Low resolution information is obtained from 
the current interlaced field, and the remaining detail information is 
obtained from a stored signal that includes a prior field or fields. The 
obtained signal can then be displayed with progressive scanning at full 
resolution, and without motion artifacts. Since only the detail signal is 
obtained from a prior field or fields, and since human vision does not as 
quickly perceive motion of high spatial frequencies, there will be little 
if any, perceived motion artifacts in the resultant displayed signal. 
However, the detail signal, including its components from prior a field or 
fields, will provide the desired resolution of the generated progressively 
scanned display. 
In accordance with an embodiment of the method of the present invention, a 
technique is provided for generating a progressively scanned video signal 
representative of images. An interlaced relatively low spatial frequency 
video signal, representative of the images, is derived at a relatively 
fast frame refresh rate; e.g. the NTSC rate of 30 frames per second 
interlaced at 60 fields per second. A relatively high spatial frequency 
video signal, representative of the images, is derived at a relatively 
slow frame refresh rate; for example, 15 frames per second or less. The 
interlaced relatively low spatial frequency video signal is connected to 
an interlaced relatively low spatial frequency signal having an increased 
number of lines, the information for each converted field coming from a 
field of the original interlaced relatively low spatial frequency video 
signal. The relatively high spatial frequency signal is converted to a 
relatively high spatial frequency signal having said relatively fast frame 
refresh rate, each field of the converted relatively high spatial 
frequency signal containing information from more than a single field of 
the original relatively high spatial frequency video signal. The converted 
low and high spatial frequency video signals are combined to obtain the 
progressively scanned video signal. 
The invention can be utilized in the context of a high definition 
television system, or can be utilized in the context of a standard 
resolution television system; the conversion to progressive scan in either 
type of system having certain performance advantages. 
Further features and advantages of the invention will become more readily 
apparent from the following detailed description when taken in conjunction 
with the accompanying drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring to FIG. 1, there is shown a block diagram of an apparatus in 
accordance with an embodiment of the invention, and which can be used to 
practice the method of the invention. In the illustrated embodiment, it is 
assumed that a conventional resolution signal (e.g. an NTSC signal), and a 
detail signal, which contains high spatial frequency components of a 
television picture and which can be combined, after suitable processing, 
with the conventional resolution signal to obtain a high definition 
television signal, are derived by receiving transmitted versions of the 
respective signals. However, it will be understood that the signals can be 
derived from any other suitable source, for example, a video recorder 
having high definition capability. As described in my above referenced 
patents, the detail signal can be transmitted and/or stored at reduced 
bandwidth by lowering its frame refresh rate, for example to a rate of 15 
or 7.5 frames per second (as compared to 30 frames per second for 
conventional NTSC television signals). This does not cause substantial 
degradation in the ultimately displayed image, since human vision cannot 
perceive changes in high spatial resolution information at as fast a rate 
as it can perceive changes in low spatial frequency information. 
In describing some of the processing in the circuitry of FIG. 1, it will be 
understood that features previously set forth in my above referenced 
patents and application, which are incorporated herein by reference, or 
which involve well-known television processing techniques, will be 
described only to the extent necessary to understand the present 
invention. The detail signal is stored in a frame memory 111 which is 
operative, as described in my above referenced patents and application, in 
conjunction with the array processor 112 and the scan converter 113, to 
receive and store the detail information at its reduced frame refresh 
rate, and to produce output detail information at a higher frame refresh 
rate, typically 30 frames per second. This is done by suitably combining 
information from a number of successive frames and applying spatial 
filtering in the horizontal and vertical directions. The result is a 
detail signal having, for example, 1125 interlaced lines, at a frame 
period of 1/30 second (and field period of 1/60 second) which contains 
picture information that includes contributions from the original image 
taken over a much longer time period, for example a 1/7.5 second period. 
The output of scan converter 113 becomes part of a signal that is 
presented in a so-called spot wobble mode, to obtain an effective 60 frame 
per second progressive scan. A high resolution display device 150 may be, 
for example, a standard type of 1125 line interlaced monitor, but equipped 
with a small deflection coil 151 that operates to wobble the spot 
vertically by one line width at a frequency of half the horizontal clock 
frequency of the detail signal. A divide-by-two circuit 115 operates on 
the horizontal clock signal (which can also be related to the clock used 
in the scan conversion of the NTSC signal components) to obtain the 
control clock for the spot wobble. 
The use of spot wobble for various purposes is well known in the art, and 
different methods of implementation can be employed. Also, as noted below, 
the invention can be implemented without using spot wobble. FIG. 2 
illustrates how two lines can be clocked out during one scan, it being 
assumed that there are 1,024 displayed lines per field, as obtained from 
the original 512 displayed lines per field of the original interlaced 1125 
total line detail signal. As seen, successive pixels to be presented are 
taken in alternating fashion from adjacent lines, and presented using spot 
wobble, at twice the pixel clock rate. 
The NTSC signal is received and processed by conventional means to obtain a 
luminance signal Y and color difference signals R-Y and B-Y (block 131). A 
scan converter 132 is then utilized to convert the Y, R-Y and B-Y signals 
to 1125 line interlaced format. This can be implemented, as is known in 
the art, by line interpolation during each field. Accordingly, for 
example, each output field (Y, R-Y, B-Y) of the scan converter has 512 
lines to be ultimately displayed. The scan converted luminance signals 
output from converters 113 and 132 are coupled to an adder 141, the output 
of which is coupled to the Y input of a matrix 145. The other two inputs 
to matrix 145 are the R-Y and B-Y signals output from scan converter 132. 
The outputs of matrix 145 are R, B, G signals that are coupled to the 
inputs of the color television display device 150. 
In operation, the spot wobble is at a clock rate that will cause the 
diagonally sampled detail signal to have successive elements be presented 
in alternating fashion between two adjacent lines (see e.g. FIG. 2). 
However, the spot wobble clock has a period that is shorter than a 
resolution element of the low spatial frequency (NTSC derived) signal, so 
this part of the signal applied to the display device will be just spread 
between adjacent lines as a result of the spot wobble. 
It will be understood that the described technique and system could be 
implemented without spot wobble, such as by scan-converting both the 
detail and the current field of the 525 line information to 1125 line 60 
frame format, and then adding them together. 
The invention also has application, for example, to scan conversion of a 
conventional interlaced signal, such as NTSC, to progressive format at 
either the same number of lines per frame or at increased number. An 
illustration is set forth in the diagram of FIG. 3. The luminance Y of an 
NTSC signal is separated, using low pass spatial filter 311 and subtractor 
312 (and suitable delay equalization not shown, which will be understood 
to be present, where required) into a low frequency Y and a detail Y. In 
this case, the Y lows are converted to 1125 line interlaced (block 321). 
The detail Y is averaged (e.g. integrated) over a suitable number of 
fields or frames (block 331) and, in this case, is also converted to 1125 
line interlaced format, and back to 30 interlaced frames per second 
(blocks 336 and 337). The two signals can then be displayed using the spot 
wobble scheme of FIG. 1. Alternatively, as previously noted, the Y lows 
and detail Y can both be converted to progressive format and combined 
without the need for spot wobble. 
The invention has been described with reference to particular preferred 
embodiments, but variations within the spirit and scope of the invention 
will occur to those skilled in the art. For example, the invention has 
application to both monochrome and color video signals and, also, the 
special processing of color signals, consistent with the way different 
colors are perceived by human vision (as set forth in my prior patents and 
application), can be advantageously employed.