Television – Format conversion – Changing number of fields for standard conversion
Reexamination Certificate
2000-12-18
2003-10-07
Miller, John (Department: 2614)
Television
Format conversion
Changing number of fields for standard conversion
C348S441000, C348S536000
Reexamination Certificate
active
06630962
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to a process and device for the frequency conversion of video signals, utilizing a dynamic calculation of the interpolation phases.
BACKGROUND OF THE INVENTION
Known frequency conversion devices are utilized, among other things, for standards conversion, for example the conversion of a PAL or SECAM 50 Hz signal into an NTSC 60 Hz signal. They are also utilized to increase the scanning frequency of television receivers, typically from 50 Hz to 100 Hz, for the purpose of improving the quality of the picture, by reducing the large area flicker.
In the general case, the frequency of the signal to be converted and the frequency of the converted signal are known in advance. The interpolation process consists in creating intermediate fields between two reference fields of the input signal to be converted. This process is shown diagrammatically in FIG.
1
.
The fields referenced
1
and
2
correspond respectively to the previous reference field of the input video sequence and to the next reference field of this sequence.
The field referenced
3
is the intermediate field to be created. This field is located temporally between the previous field and the next field, at an instant defined by a value &agr; corresponding to the interpolation phase.
If t
prev
and t
next
correspond to the instants relating to the previous field and to the next field, the instant t
interp
relating to the intermediate field to be interpolated is then:
T
interp
=
t
prev
+
α
(
t
next
-
t
prev
)
=
t
next
-
(
1
-
α
)
(
t
next
-
t
prev
)
In a known manner, the interpolation processing can call upon linear filtering utilizing spatio-temporal filters with finite impulse response, or upon motion-compensated interpolation.
The processing methods utilized require knowledge of the interpolation phase for each field to be interpolated.
In the case where the input or output signal is not bound to a standard defining its frequency, a conversion device specific to these signals and in particular to their scanning frequency characteristic must be designed. This specificity naturally generates high costs. Moreover, modification of the scanning characteristics of a signal renders such a device unutilizable or, at the least, requires either manual intervention to render it compatible with the modified signal or signals, or the presence of circuits specific to these new characteristics.
The aim of the invention is to alleviate the aforesaid drawbacks.
SUMMARY OF THE INVENTION
To this end, the invention relates to a process for the field or frame frequency conversion utilizing a dynamic calculation of the interpolation phases, of an input video signal at a frequency F
1
defined by a synchronization signal S
1
into an output video signal at a variable frequency F
2
defined by a synchronization signal S
2
, comprising a writing of the input signal to a memory on the basis of a write pointer P
W-IN
, and a reading, from the memory, to obtain the output signal, characterized in that it stores the position of the write pointer P
W
on receipt of the synchronization signal S
1
so as to provide a value P
W-IN
, and on receipt of the synchronization signal S
2
so as to provide a value P
W
—
OUT
, in that it dynamically calculates an interpolation phase &agr; such that:
α
=
P
W
_OUT
-
P
W
_IN
Δ
P
W_FIELD
if
P
W_OUT
≥
P
W_IN
or
α
=
P
W_OUT
+
N
CAP
·
Δ
P
W_FIELD
-
P
W_IN
Δ
P
W_FIELD
if
P
W_OUT
<
P
W_IN
&Dgr;P
W
—
FIELD
being the memory quantity required for the storage of a field or frame of the input signal and N
CAP
the capacity of the memory expressed in terms of number of fields or frames,
and in that it performs a phase interpolation corresponding to this value.
According to a particular characteristic, three or four successive fields or frames are simultaneously stored in a memory and the interpolation is performed on the fields or frames preceding that being stored upon receipt of the signal S
2
utilized for the calculation of the interpolation phase, on the basis of this calculated interpolation phase.
According to another characteristic, the calculation of the interpolation phase takes into account a shift of the write pointer corresponding to the duration of the field or frame blanking signal before the active video.
The invention also relates to a dynamic frequency conversion device for converting an input signal at a frequency F
1
defined by a synchronization signal S
1
into an output signal at a variable frequency F
2
defined by the receipt of a synchronization signal S
2
, comprising a memory for writing the input signal on the basis of a write pointer P
W
, an interpolation circuit receiving the outputs from the memory for read-access to a preceding field or frame T
1
and read-access to a next field or frame T
2
, characterized in that it also comprises:
a circuit for storing the pointer P
W
on receipt of the signal S
1
so as to provide a value P
W
—
IN
,
a circuit for storing the pointer P
W
on receipt of the signal S
2
so as to provide a value P
W
—
OUT
,
a circuit for calculating interpolation phase
α
=
P
W
_OUT
-
P
W
_IN
Δ
P
W_FIELD
if
P
W_OUT
≥
P
W_IN
or
α
=
P
W_OUT
+
N
CAP
·
Δ
P
W_FIELD
-
P
W_IN
Δ
P
W_FIELD
if
P
W_OUT
<
P
W_IN
&Dgr;P
W
—
FIELD
being the memory quantity required for the storage of a field or frame of the input signal and N
CAP
the capacity of the memory expressed in terms of number of fields or frames,
and in that the interpolation circuit is coupled to the calculating circuit so as to receive this interpolation phase and calculate the interpolated field or frame as a function of the interpolation phase.
By virtue of the invention, the process automatically calculates the interpolation phase corresponding to the output signal to be generated, when the scanning frequency of this output signal is not known a priori.
The device obtained is compatible with any type of output signal, at least in a wide frequency range. The device is simple to implement and cheap. It makes it possible to supply adjustable scanning frequency apparatuses, such as monitors of PC-type personal computers.
REFERENCES:
patent: 5651031 (1997-07-01), Ishizu
patent: 6288745 (2001-09-01), Okuno et al.
patent: 6331862 (2001-12-01), Yamada et al.
patent: 6407775 (2002-06-01), Frink et al.
patent: 6480232 (2002-11-01), Wilson et al.
patent: 0323198 (1989-07-01), None
EPO Search Report dated: Sep. 13, 2000.
Babonneau Jean-Yves
Clerc François Le
Duffy Vincent E
Kurdyla Ronald H
Miller John
Thomson Licensing S.A.
Tran Trang U.
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