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| United States Patent |
5,452,011 |
| Martin , et al. |
September 19, 1995 |
Method and device for film-mode detection and field elimination
Abstract
A method for determining which of similar video fields may be excised to
enhance video signal compression evaluates parameters of four successive fields
denoted 0, 1, 2, and 3. Accumulated differences d(0, 2) and d(1,3) of
corresponding pixels in successive frames are generated. In addition a
determination is made whether fields 1 and 2 exhibit interlace characteristics.
If they do not exhibit interlaced characteristics, a comparison is made of d(0,
2) and d(1, 3). If d(0, 2) is less than d(1, 3) by a predetermined amount, field
2 is excised from the signal stream and a code is generated to condition a
receiver to display two of the remaining four fields in a three field interval.
Subsequently the latter two fields of the set of 0, 1, 2 and 3 fields, and the
next two occurring fields are similarly analyzed.
| Inventors: |
Martin; Alix (Paris, FR); Smith;
Michael (Los Angeles, CA) |
| Assignee: |
Thomson Consumer Electronics, Inc.
(Indianapolis, IN) |
| Appl. No.: |
212746 |
| Filed: |
March 14, 1994 |
| U.S. Class: |
348/526; 348/97; 348/449;
348/459; 348/102 |
| Intern'l Class: |
H04N 005/08 |
| Field of Search: |
348/526,97,101,102,103,105,106,449,459,446,558,911
|
References Cited [Referenced
By]
U.S. Patent Documents
| 4641188 |
Feb., 1987 |
Dischert |
358/140. |
| 4703358 |
Oct., 1987 |
Flannaghan |
358/167. |
| 4982280 |
Jan., 1991 |
Lyon et al. |
358/105. |
| 5111511 |
May., 1992 |
Ishii et al. |
382/1. |
| 5191427 |
Mar., 1993 |
Richards et al. |
358/214. |
Primary
Examiner: Groody; James J.
Assistant Examiner: West; Nina M.
Attorney, Agent or Firm: Tripoli; Joseph S. Herrmann; Eric P.
Kurdyla; Ronald H.
Claims
1. A method for determining which of fields in a sequence of fields of
video signal may be excised to enhance signal processing if respective field
pairs do not exhibit interlace characteristics, said method comprising:
for a sequence of four successive fields 0, 1, 2, 3;
generating
accumulated differences d(0, 2) and d(1,3) of corresponding pixels in successive
frames;
determining whether fields 1 and 2 exhibit interlaced
characteristics;
if fields 1 and 2 do not exhibit interlaced
characteristics, comparing the accumulated differences d(0, 2) and d(1, 3); and
if d(0, 2) are less than d(1, 3) by a predetermined amount, excising the
third occurring field 2.
2. The method set forth in claim 1 further
comprising;
if d(0, 2) are less than d(1, 3) by said predetermined
amount, grouping fields 0 and 1 of the four field sequence as a video frame and
generating a code to condition a receiver to display fields 0 and 1 in a field
sequence 0, 1, 0 in a three field interval.
3. The method set forth in
claim 1 further comprising:
generating accumulated differences d(1, 2)
between vertically aligned pixels in successive interlaced lines of fields 1 and
2 and generating accumulated differences d(2, 3) between vertically aligned
pixels in successive interlaced lines of fields 2 and 3; and
on the
condition that the accumulated differences d(0, 2) are not less than d(1, 3) by
said predetermined amount, comparing the accumulated differences d(1, 2) and
d(2, 3); and
if the accumulated differences d(1, 2) are less than the
accumulated differences d(2, 3) by a further predetermined amount, excising
field 0 of said sequence of fields 0, 1, 2 and 3.
4. The method set
forth in claim 3 further comprising:
on the condition that the
accumulated differences d(1, 2) are less than the accumulated differences d(2,
3) by said predetermined amount, grouping fields 1 and 2 of the four field
sequence as a video frame and generating a code to condition a receiver to
display fields 1 and 2 in a field sequence 2, 1, 2 in a three field interval.
5. The method set forth in claim 2 further comprising:
on the
condition that the accumulated differences d(0, 2) are not less than d(1, 3) by
said predetermined amount, and that the accumulated differences d(1, 2) are not
less than the accumulated differences d(2, 3) by said further predetermined
amount, grouping fields 0 and 1 as a frame and generating a code to condition a
receiver to display fields 0, 1 in a two field sequence of 0, 1.
Description
This invention relates to a method and apparatus for determining if a
video signal has characteristics of signal originated in interlaced scan mode
i.e., video mode or has characteristics of signal originated as non-interlaced
scan or film mode.
BACKGROUND OF THE INVENTION
Certain high end
television receivers include apparatus to enhance the apparent resolution of
reproduced images by, for example, converting interlaced scanned images to
non-interlace scanned images. Apparatus of this type typically introduces image
artifacts in areas of image motion. These artifacts can be significantly reduced
with knowledge of whether the source material was originally generated as
interlace scanned video or as non-interlace scanned video or film. In addition
video signal compression systems, particularly for use with NTSC video signals,
can realize a twenty percent compression bonus if the source video can be
determined to have been originated as film and converted to video by the
technique known as 3:2 pull down. Video signal generated via 3:2 pulldown
includes one duplicated field in every 5 field sequences, which duplicate fields
may be excised to realize the compression bonus.
SUMMARY OF THE
INVENTION
The apparatus and method according to the invention determines
which of successive video fields may be excised prior to compression to
eliminate fields that are substantially identical to prior fields. The apparatus
evaluates parameters of four successive fields denoted 0, 1, 2, and 3.
Accumulated differences d(0, 2) and d(1,3) of corresponding pixels in successive
frames are generated. In addition a determination is made whether fields 1 and 2
exhibit interlace characteristics. If they do not exhibit interlaced
characteristics, a comparison is made of d(0, 2) and d(1, 3). If d(0, 2) is less
than d(1, 3) by a predetermined amount, field 2 is excised from the signal
stream and a code is generated to condition a reciprocal receiver to display two
of the remaining four fields in a three field interval. Subsequently the latter
two fields of the set of 0, 1, 2 and 3 fields, and the next two occurring fields
are similarly analyzed. The invention will be described with greater specificity
with the aid of the following drawings.
BRIEF DESCRIPTION OF THE
DRAWINGS
FIG. 1 is a block diagram of an interlace/non-interlace field
characterizer embodying the present invention.
FIG. 2 is a flow chart of
the operation of a first aspect of the FIG. 1 apparatus.
FIG. 3 is a
flow chart of the operation of a second aspect of the FIG. 1 apparatus.
DETAILED DESCRIPTION
Referring to FIG. 1, video signal to be
analyzed for interlace scan characteristics is provided from a source 10 which
may be a video recorder. The video signal is coupled to an input terminal of a
field memory 12, an input terminal of a one horizontal line memory 16, and to
respective first input terminals of subtractors 17, 18 and 19. The video signal
is delayed by one field interval in the memory 12 and the delayed video signal
is coupled to a second similar field memory 14 and to a second input terminal of
the subtractor 18. The video signal is delayed by one horizontal line interval
in the memory 16, the output of which is coupled to a second input terminal of
the subtractor 19. Video signal applied to the memory 14 is delayed for a second
field interval and coupled to a second input terminal of the subtractor 17, to
the input terminal of a buffer storage frame memory 25, and to the Decision and
Field Combine circuitry 26.
Each of the subtractors 17, 18 and 19
provide at their respective output terminals the magnitude of the differences of
the signals applied to their respective input terminals. Subtractor 17 provides
the magnitudes of the differences of the amplitudes of corresponding pixels in
successive frames. These magnitude values are accumulated over respective frame
intervals. It has been determined to be advantageous to accumulate magnitude
values only over the active picture portions of respective frame intervals., The
accumulation period is controlled by the circuit 26, and accumulated magnitude
values for respective frames d(j, j+2) are captured and stored by the circuit
26.
The subtractor 18 provides the magnitudes of the differences of the
amplitudes of corresponding pixels in successive fields. That is, subtractor 18
provides the magnitudes of the differences of pixels in adjacent lines in a
frame comprised of two successive fields j and j+1. The magnitudes of the
differences from exclusive pairs of lines are accumulated during the active
picture interval in accumulator 22. Preferably the magnitudes are accumulated
over strips FR(k) of the frame with each strip including about 16 line
intervals. The accumulation intervals are controlled by the circuit 26 which
captures and stores accumulated values for respective strips.
Let Y(m,
n) be the luminance value at coordinates (x=m, y=n) in the current frame, and k
be the strip number (k=0, . . . 14 for NTSC and k, . . . 17 for PAL). For each
strip in the luminance plane, the differences FR(k) of pixels belonging to
opposite fields, i.e., adjacent lines in a frame are equal to ##EQU1##
The subtractor 19 provides the magnitudes of differences of vertically
aligned pixels in adjacent lines in exclusive fields. These differences, for
exclusive line pairs, are accumulated over the active picture interval for
strips FD(k) of respective fields. The accumulation intervals are controlled by
the circuit 26 which captures and stores accumulated values for respective
strips. For each strip in the luminance plane, the differences FD(k) of pixels
belonging to exclusive fields, i.e., adjacent lines in a field are equal to
##EQU2## The line numbering for both field and frame strips assumes ordinal line
numbering over a frame interval. That is, lines in the even fields are numbered
0, 2, 4, . . . etc. and lines in the odd numbered fields are numbered 1, 3, 5,
7, etc.
The differences generated by the subtractor 18 are also coupled
to a further accumulator 23, which accumulates the pixel differences over the
entire active portion of respective fields. The accumulated values over a frame
d(j, j+1) are captured and stored by the circuit 26, for use in determining
which of respective fields are to be excised from the field sequence.
The Decision and Field Combining Circuit 26 of FIG. 1 performs two
functions. The first is to determine if successive fields comprise interlace
scan fields, and secondly, based on this determination to combine fields into
frames for application to video signal compression apparatus which compresses
video signal on a frame by frame basis.
The operation of the first
function is illustrated by the flow chart of FIG. 2. Two successive fields, j
and j+1, are used for this analysis. The system is initialize at a step 50 which
occurs when the circuitry is energized. Initialization involves setting
respective index values to zero. After initialization the system waits {51} for
the next field to occur. When a new field occurs, two indices k and r are set to
zero {52}. The k index is a strip index number and the r index is a count of a
measurement event to be described subsequently. Once the indices are reset, a
stored accumulated magnitude value FR(k) for strip k is accessed {53} from
memory. Recall that the value FR(k) corresponds to line-to-line pixel
differences within a frame comprised of fields j and j+1. The stored accumulated
magnitude values FD.sub.j (k) and FD.sub.j+1 (k) are also accessed {53} from
memory. These values correspond to line-to-line pixel difference values within
respective fields j and j+1.
The values FD.sub.j (k) and FD.sub.j+1 (k)
are added together in step {54} to form the value FD(k). The ratio R=FR(k)/FD(k)
is calculated {55}. This ratio is compared {56} to a predetermined threshold
value W (such as 1). If the ratio is less than the threshold a jump is made to
step {59}. If the ratio is greater than the threshold the index r is incremented
by one unit {57}.
The index r is examined {58} to determine whether it
is greater or lesser that a second predetermined threshold value M. If it is
greater than M, the frame consisting of fields j and j+1 are presumed {61} to
exhibit interlaced characteristics. That is, there is for example, apparent
motion between the successive fields, and motion cannot occur between field
intervals of film sourced video or progressive scanned video. The inventors have
determined that if three strips exhibit a ratio R greater than W (i.e., M=3),
this is sufficient information to consider the frame to consist of interlaced
fields. After classifying a frame as interlaced, the system returns to step {51}
to await the next field.
If at step {58} the index r is not greater than
M, the strip index k is incremented by one unit {59}. A test is performed {60}
to determine if all strips have been processed. If so the system jumps to step
{51} to await the next field, and if not the system jumps to step {53} to
process the next strip.
In a video signal compression system it is
desirable to excise repeated fields of information, and in lieu of transmitting
the excised fields in compressed form, to transmit a code to indicate that the
field has been excised and that a given transmitted compressed field may be
repeated as a substitute for the excised information. FIG. 3 is a flowchart
which illustrates this function which is performed by the Decision and Field
Combine element 26. In performing this function the system uses the
interlace/non-interlace determinations of two frames (four fields 0, 1, 2, 3)
from the input field sequence to make all decisions. The numbers 0, 1, 2, 3
refer to each consecutive set of occurring four fields and field 0 may be an
even or odd field.
Referring to FIG. 3, this function is initialized
{101} to determine if sufficient field information is available, and then
accesses the interlace/non-interlace classifications of fields (1,2) and (0,1).
A test {103} is performed to determine if fields 1 and 2 are interlaced. If they
are, the system jumps to step {109} where a test is performed to determine if
fields (0,1) are interlaced. If they do not have non-interlaced characteristics,
fields 0 and 1 are grouped {111} as a frame and indicated as being
non-interlaced. A code is generated to indicate that they should be displayed in
the field order 0, 1. Alternatively, if they do have interlaced characteristics,
fields 0 and 1 are grouped {117} as a frame and indicated as being interlaced
and a code is generated to indicate that they should be displayed in the field
order 0, 1.
Alternatively at step {103}, if the fields (1, 2) are
indicated as non-interlaced, a test is performed to determine if field 2 is
substantially similar to field 0 and field 1 is dissimilar to field 3. This is
accomplished by comparing the accumulated pixel differences d(0, 2) between
fields 0 and 2 with the pixel differences d(1, 3) between fields 1 and 3. (The
differences d(0, 2) and d(1, 3) are provided by the subtractor 17 and
accumulator 20). If the differences d(0, 2) are significantly smaller than the
differences d(1, 3), the assumption is made {113} that the source video signal
is non-interlaced, for example it may have been generated by the process known
as 3:2 pulldown. The third field (field 2) is excised from the video signal, and
fields 0 and 1 are grouped as a frame. A code is generated indicating that field
2 has been excised and that fields 0 and 1 should be displayed (when recovered
and decompressed) in a three field interval with the field sequence 0, 1, 0. The
system returns to step {103} and waits for the next fields.
At step
{105}, if the differences d(0, 2) are not significantly smaller than the
differences d(1, 3), a further test {107} is performed. This test is included to
detect the special case where an isolated field is included which is basically
out of sequence such as may occur during editing. The accumulated pixel
differences d(1, 2) between fields 1 and 2 are compared with the pixel
differences d(2, 3) between fields 2 and 3. (These differences are provided by
accumulator 23.) If the differences d(1, 2) are significantly smaller than the
differences d(2, 3), the assumption is made {115} that an isolated field (field
0) is present, which field is excised from the field sequence. Fields 1 and 2
are grouped as a frame and a code is generated indicating that upon recovery and
decompression the fields 1 and 2 should be displayed in the three field sequence
2, 1, 2. Thereafter the system returns to step {103} and waits for the next
fields.
If the differences d(1, 2) are not significantly smaller than
the differences d(2, 3), fields 0, 1 are tested {109} for interlace. If fields 0
and 1 are interlaced they are grouped as a frame and a code is generated
indicating that they should be displayed in the sequence 0, 1. Alternatively,
the fields are grouped 0, 1 and a code is generated {111} indicating they are
not interlaced but should be displayed in the sequence 0, 1. The system then
returns to step {103}.
At step {105}, it has been found that an
inequality in the order of about 1.5 or greater is satisfactory. At step {107},
it has been found that an inequality in the order of 3.0 or greater is
satisfactory.
Referring again to FIG. 1, at least the former two fields
0 and 1 of fields 0, 1, 2, and 3 are available to the Decision and Field
Combiner from the frame memory 25, when respective grouping decisions are
completed. Field 2 is available from field memory 14 and field 3 is available
from field memory 12. Depending on the grouping decision, appropriate fields are
combined as frames and provided to the MPEG compressor/encoder 27. In addition
the respective codes indicating excised fields and field display sequences are
passed to the MPEG compressor/encoder 27 for inclusion in the encoded video
signal for storage or transmission.
* * * * *
