JPH01176192A - Scanning converter for television signal - Google Patents

Abstract

PURPOSE:To improve picture quality after conversion by processing optimizingly the resolution of 2:1 interlace scanning and the trade-off of loopback component after the scanning conversion in response to the signal component of a television input picture of the sequential scanning or the interlace scanning with difference scanning line number. CONSTITUTION:When a signal band-limited in a characteristic of M1 is converted into an interlace signal, spectrum signals (b), (c) are obtained. The loopback component is extended up to a low frequency as shown in figure according to the characteristic and a large crosstalk takes place with respect to the original component, but the original component is not almost attenuated to an extent of nu=1125/4 and an excellent vertical spatial resolution is provided. When the quantity of loopback is within a permissible range visually, a moving picture with excellent sharpness is obtained. On the other hand, when a signal band-limited in the characteristic of M2 is converted into an interlace signal, spectrum signals (d), (e) are obtained. The band of the original component is made narrow in this characteristic and loopback component does not almost appear below nu=1125/4. Thus, the picture quality disturbance in the converted picture due to loopback component is avoided.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a scanning converter for television signals, and in particular, to a scanning converter for television signals, and particularly for scanning from a progressive scanning signal or a 2:1 interlaced signal with a different number of scanning lines to a 2=1 interlaced signal. It concerns the spatio-temporal band limitation of the transducer.

(Summary of the Invention) The present invention relates to spatio-temporal band limiting processing of an input signal prior to conversion of a television signal by a sequential-to-interlace converter or a scanning line number converter, and the converter includes still image filter control means. The re-controlling means includes two types of low-pass filters each having a different pass band, and the mixing of two output signals from the two types of filters. The ratio is controlled by the amount of vertical spatial frequency components in each predetermined band.

In this way, the optimum conditions for the sharpness and aliasing components of the converted image are adaptively obtained.

(Prior Art) Conventionally, motion adaptive scanning uses fixed filters for still images and moving images as a spatiotemporal band limit when converting a progressive scanning signal or a 2:1 interlaced signal with a different number of scanning lines into an interlaced signal. There was a converter.

(Problem to be Solved by the Invention) In a progressive interlaced scan converter or a scanning line number converter, band limitation is performed in the spatiotemporal frequency domain in order to prevent image quality deterioration due to aliasing components based on interlaced scanning after scan conversion. Scan conversion was performed from In conventional converters, this band limitation is performed using motion adaptive processing, and fixed spatiotemporal filters are applied to each of still images and moving images. but,
In this method, the vertical spatial frequency band is 172, which degrades the resolution, especially for moving images. Furthermore, due to the imperfection of the filter, even in the 1/2 band, depending on the image, the image quality may deteriorate due to aliased components after conversion, resulting in unsightly appearance. In an attempt to prevent this, making the video filter even narrower has the disadvantage of further degrading the resolution of other video images.

SUMMARY OF THE INVENTION An object of the present invention is to provide a television signal scan converter that eliminates the above-mentioned drawbacks and can optimize the trade-off between the resolution after conversion and the aliasing component.

(Means for Solving the Problems) To achieve this object, the television signal scan converter of the present invention converts television progressive scanning signals or 2:1 interlaced scanning signals having different numbers of scanning lines into 2:1 interlaced scanning signals. In a scan converter that performs spatio-temporal band limiting processing on an input signal prior to conversion in scan conversion to a signal, the converter includes at least one of a still image filter control means and a moving image filter control means. , the still image filter control means includes two low-pass filters for still images having a wide band and a narrow band for vertical spatial frequencies as filters that perform band limitation on still images, and the still image filter control means includes two low-pass filters for still images, one having a wide band and a narrow band for vertical spatial frequencies, and controlling the vertical high frequency components of the vertical spatial frequency of the input signal. means for controlling the mixing ratio of the re-output components of the two still image low-pass filters according to the amount of the still image low-pass filter, and the video filter control means is configured to control the mixing ratio of the re-output components of the two low-pass filters for still images, and the video filter control means is configured to control the mixing ratio of the re-output components of the two low-pass filters for still images. Means for controlling the mixing ratio of the re-output components of the two low-pass filters for moving images according to the amount of vertical mid-range components of the vertical spatial frequency of the input signal, comprising two narrow-band low-pass filters for moving images. It is characterized by:

(Embodiments) The scan converter of the present invention will be described in detail below by way of embodiments with reference to the accompanying drawings.

FIG. 1 shows a block diagram of an embodiment of the scan converter of the present invention. The input signal is a television progressive scan signal,
The output signal is a 2:1 interlaced signal having the same number of scanning lines as the input signal.

In FIG. 1, input signals are directed to field (F) memories 1, 2 connected in cascade.

Here, the input signal, the output of F memory 1, and the output of F memory 2 are each a signal f to distinguish the time (field).
It is called l+fO+f-1. These signals are first led to coefficient multipliers 3 and 4.5, respectively, and are respectively divided into coefficients 1/4.1/2.
Multiplyed by 1/4. These resultant signals are added in an adder 6. These blocks 3 to 6 collectively constitute a temporal filter 7 which is a band limiting filter for still images. The signal f0 is also input to vertical filters 9 and 10. The vertical filters 9 and 10 are in-field vertical spatial filters having no attenuation characteristics in the time direction, and their specific configuration can be realized, for example, by the configuration shown in the second diagram. Second
In the figure, one line (H) delay devices 31 to 36 are connected in cascade, and have coefficient multipliers 37 to 43 at the filter input signal and the output tap of each H delay device. Value of each coefficient α3 ~ α−
3 determines the spatial frequency characteristics in the vertical direction. Next, the respective outputs of the coefficient units 37 to 43 are added together in an adder 44 to form a filter output signal. These are 7-tap vertical filters, and the filter output signal is 3 taps relative to the input signal.
H is delayed.

The outputs of the vertical filters 9 and 10 in the first illustrated block diagram are mixed in a mixer 11 according to a control signal to be described later, and become a moving image input to a switch 12. The output of the still image filter is n for delay matching with the vertical filters 9 and 10.
, H (n is an integer) delay device, and is led to the static side input of the switch 12. The value of the integer n1 is, for example, the vertical filter 9
, 10, if the configuration shown in the second figure is used, n, ・3
becomes. The switch 12 connects the two inputs to the motion detection circuit 1.
The switching is performed according to the motion signal outputted from No. 4. The motion detection circuit can be realized using the signals f,, fo, f,, . . . as input signals using known techniques.

The output of the switch 12 is scan-converted by a scan conversion circuit 13 and becomes an output signal of 2:1 interlaced scanning.

On the other hand, a subtracter 15 obtains a difference signal between the signals f1 and f-. This difference signal and signal f0 are switched by a switch 16. This operation will be detailed later.

The output of switch 16 is nJ (nz is an integer) delay device 1
7 input. This delay device is used to match the delay of the control signal and the vertical filters 9 and 10, which will be described later, and when the vertical filter having the configuration shown in the second figure is used, nz=32=1. The output of the nJ delay device 17 is led to a cascade-connected 2H delay device 18°19, and the outputs of the delay devices 17 to 19 are each inputted to a coefficient multiplier 20°2L 22 with a coefficient of -1/4.1/2. -1/4 is multiplied.

These results are added in an adder 23, and the absolute value circuit (A
BS) 24 input. These blocks 18 to 23 constitute a vertical mid-pass filter whose pass band is the mid-range component of the vertical spatial frequency.

The characteristics of the absolute value circuit 24 are as shown in FIG. 3, for example. Set up a certain amount of uncertainty for the input level,
For levels higher than that, an output level linear with the absolute value of the input is output. At this time, as shown by the dotted line, non-linear level conversion may be performed such that the output image quality of the apparatus is optimized for the absolute value of the input. The dead zone is for removing noise components and the like.

The output of the absolute value circuit 24 becomes a control signal for controlling the mixing ratio of the mixer 11. For example, when the level of the control signal is low, the output point of the mixer 11 is placed on the vertical filter 9 side, and when it is high, the output point is placed on the vertical filter 10 side. In this case, the vertical filter 9 is used as a wideband filter for moving images, and the vertical filter 10 is used as a narrowband filter for moving images.

Next, using the band characteristic examples shown in FIGS. 4 and 5, we will compare the conventional example (
The differences between the scan converter (FIG. 4) and the scan converter of the present invention (FIG. 5) will be explained in order.

FIG. 4(a) shows band limitations in the spatio-temporal frequency domain in a conventional scan converter from progressive scanning to interlaced scanning.

In the figure, the horizontal axis is the temporal frequency f (Hz), the vertical axis is the vertical spatial frequency ν (cycle), and the signal has a scanning line number of 1.
It is assumed that there are 125 signals and a field frequency of 60 Hz. Conventionally, as shown in the figure, for still images, time frequency (
For videos, band limitation is performed only in the vertical spatial frequency (ν) direction, and the area in both cases is ν=
1125/2 or less and 1/2 of the area below f = 30Hz
It is. By doing this, based on interlace scanning after conversion to an interlace signal, it is possible to prevent the aliasing component from visually reaching the low frequency range and to prevent crosstalk between the original component and the aliasing component. can be understood from Figure 4(b), which shows the spectrum of an interlaced signal converted from a still image, and Figure 4(c), which shows the spectrum of a signal converted from a moving image.C8 in both figures is based on interlaced scanning (sampling). It is a carrier. Figure 4 (
In b) and (c), band limiting for still images has a higher vertical spatial resolution than band limiting for moving images, but since it has attenuation characteristics in the time-frequency direction, it causes blurring, double images, etc. for moving images. For this reason, a motion detection circuit detects the component in the area indicated by the dotted line in FIG. 4(a), and when this component is large, band limitation for moving images is used.

Band-limiting for moving images has no attenuation characteristics in the time direction, so it can be realized by an in-field vertical filter, but its characteristics usually have imperfections due to hardware limitations. For example, in the case of a filter configuration with about 7 taps as shown in FIG. 2, its characteristics will be as shown in FIG. 4(d).

In the case of a characteristic of this level, the response decreases even when ν=1125/4 or less, and when this characteristic is used, it becomes a concern that the vertical spatial resolution of a moving image is poor. Furthermore, the aliasing component indicated by diagonal lines in FIG. 4(d) extends to the low range below ν=1125/4, and therefore, depending on the image, the aliasing component becomes a noticeable disturbing component.

FIG. 5(a) shows an example of the characteristic of band limitation by the scan converter of the present invention. The conditions in this figure are the same as those in FIG. 4(a). In Fig. 5(a), the band limit for still images is the same as in Fig. 4(a), but the band limit for moving images is the same as in Fig. 4(a).
and Dynamic 2. Dynamic 1 has a wide band characteristic with a pass band of ν=1125/4 or more, and Dynamic 2 has a narrow band characteristic with a passband of ν=1125/4 or less. Figures (b) and (c) convert a signal band-limited with the characteristic of motion 1 to an interlaced signal.
A signal with a spectrum like this is obtained. According to this characteristic, as shown in the figure, the aliasing component extends to the low frequency range, causing large losstalk with the original component, but the original component is
It is hardly attenuated up to about 25/4 and has good vertical spatial resolution. Therefore, if the amount of aliasing components is within an allowable range when viewed, a moving image with good sharpness can be obtained by utilizing this characteristic. On the other hand, when converting a signal band-limited with the characteristics of dynamic 2 to an interlaced signal, the same figure (d)
, (e) is obtained. With this characteristic, the band of the original component also becomes narrow, but the aliasing component hardly appears below ν=1125/4. Although the converted image quality due to this characteristic is somewhat poor in sharpness, there is no image quality interference due to aliasing components.

To the human eye, image quality disturbance exceeding the allowable limit is perceived as a greater deterioration in image quality than poor sharpness, so when the aliasing component is large, it is preferable to use the dynamic 2 characteristic in terms of image quality. In the circuit shown in FIG. 1, the amount of the component in region A or region B of the characteristic shown in FIG. 5(f) is detected by the switch 16 and used as a control signal for switching the band of the vertical filter.

In FIG. 1, when the switch 16 is turned to the C side, a component in the area is detected, and when it is turned to the D side, the component in the area B, which is band-limited in the time direction, is detected in the area A.

Regions A and B both have characteristics as shown in FIG. 5(g) in the vertical direction, and correspond to the middle range in vertical spatial frequency. Region A is a region where the characteristics of Motion 1 and Motion 2 are different, and it can be seen that switching between Motion 1 and Motion 2 can be achieved by detecting the component of this region and controlling the amount to an appropriate amount. In this case, instead of using the circuits of blocks 17 to 23, the difference between the output signals of the vertical filters 9 and 100 may be input to the ABS 24. However, since area A also includes a still image area, it may be better to detect the component from area B, which is a purely moving image component and is an area where aliasing is noticeable after scan conversion. . This switching can be determined by comprehensively considering the converted image quality.

FIG. 6 is a block diagram of another embodiment of the scan converter of the present invention. In addition to the functions of the circuit having the configuration shown in the first diagram, the circuit having this configuration can also switch the characteristics for still images in accordance with the input signal.

In Fig. 6, the band limit for still images is the spatiotemporal filter 5.
3.54. The filters 53 and 54 are filters that limit the band not only in the time direction but also in the vertical direction like the time filters shown in FIG.
This can be realized using a known technique using f-+ as an input. The outputs of filters 53 and 54 are mixed in mixer 57 according to control signal 2 and become the quiet input of switch 59. The control signal 2 is based on the result of detecting the amount of the vertical high frequency component of the signal f0 by the vertical high frequency detection circuit 63, and is generated by the blocks 17 to 17 of the configuration shown in the first diagram.
It is made by a circuit similar to 24. The other circuits in the configuration shown in FIG. 6 are similar to the corresponding circuits in FIG.

FIG. 7(a) is an example of characteristics used in the spatio-temporal filter for still images shown in FIG. Still 1 has the same characteristics as the still image characteristic shown in FIG. 4, and Still 2 has the characteristic of Still 1 further band-limited in the ν direction. Switching between the two is performed depending on the amount of the component in region X, which is the vertical high frequency component. When a signal band-limited using static 2 characteristics is converted into an interlaced signal, a signal having a spectrum as shown in FIG. 7(b) is obtained.

According to this characteristic, the spatial resolution of a still image is lower than that of a still image, but the component of the region Y in the figure does not occur as an aliasing component.

Region Y is a component that is noticeable as interline flicker disturbance, and the occurrence of this disturbance can be prevented by using the characteristics of static 2.

In addition to the signals shown here, the present invention can also be used, for example, when the number of scanning lines is 52.
It can also be used for 5 signals. Furthermore, it can be used not only as a sequential interlaced converter but also as a scanning line number converter that converts from 1125 scanning lines to 525 or 625 scanning lines, for example.

Furthermore, in the embodiment of the present invention, a motion detection circuit is provided to perform motion adaptive processing for switching between still images and moving images, but this processing is not necessarily required in the present invention.

Although other embodiments of the present invention use both dynamic 1 and dynamic 2 filter switching and static 1 and static 2 filter switching, the object of the present invention can be achieved using either one.

(Effects of the Invention) As described above in detail, by using the television signal scan converter of the present invention, it is possible to convert signals according to signal components of sequential scanning or interlaced scanning television input images having different numbers of scanning lines. The trade-off between the resolution of the 2:1 interlace scan image after scan conversion and the aliasing component can be optimally processed, and the image quality after conversion can be improved.

[Brief explanation of the drawing]

FIG. 1 shows a configuration block diagram of an embodiment of the scanning converter of the present invention, and FIGS. 2 and 3 show an example of the configuration of a vertical filter and an absolute value circuit used in the converter having the configuration shown in FIG. Characteristic examples are shown in Figures 4 (a) to (d) and Figures 5 (a) to (g), respectively.
Diagrams for explaining band limitations in conventional and inventive converters are shown, respectively. FIG. 6 is a block diagram of another embodiment of the present invention, and FIG. 7 is a block diagram of the configuration of another embodiment of the present invention. FIG. 3 is a diagram illustrating an example of band limitation. 1, 2.5L 52...Field memory (F) 3~
5, 20 to 22. 37 to 43... each coefficient unit 6, 23.
44...Adder 7...Band limit time filter 8, 17.18.19.31-36...Each delay device 9,
10.55.56...Vertical filter LL 57.58
... Mixer 12, 16.59... Changeover switch 13, 60.
...Scan conversion circuit 14, 61...Motion detection circuit 15...Subtractor 24...Absolute value circuit (ABS) 53, 54...Spatio-temporal filter 62...Vertical mid-range detection circuit 63...・Vertical high frequency detection circuit 4th diagram
(Q) Figure 5 Figure 6 / #tIllllification control da J (Yarienku Figure 7 transformation example) Kunio 1, Indication of the case 1986 Patent Application No. 335693 2, Name of the invention Person who corrects scanning converter 3 for television signals Relationship to the case Patent applicant (435) Japan Broadcasting Corporation 4, Agent 1. "Visual time" on page 11, line 20 of the specification is changed to "visual"
Correct to. 2. On page 16, line 16, change “Figure 7 is” to “Figure 7 (
a) and (b) are corrected to ``. (Corrected diagram) Figure 7: Example of a tilted example

Claims (1)

[Claims] 1. When converting a television progressive scanning signal or a 2:1 interlaced scanning signal with a different number of scanning lines into a 2:1 interlaced scanning signal, spatiotemporal band limiting processing of the input signal prior to conversion is performed. In the scanning converter for performing the scan converter, the converter is provided with control means for at least one of a still image filter control means and a moving image filter control means, and the still image filter control means is configured to perform vertical space filtering as a filter that performs band limitation on still images. Equipped with two low-pass filters for still images, one wideband and one narrowband frequency.
Means for controlling a mixing ratio of both output components of the two low-pass filters for still images according to the amount of a vertical high-frequency component of a vertical spatial frequency of an input signal; Two video low-pass filters with a wide band and a narrow band for vertical spatial frequencies are provided as limiting filters, and the two video low-pass filters are adjusted according to the amount of vertical mid-range components of the vertical spatial frequency of the input signal. A scan converter for a television signal, characterized in that it is means for controlling the mixing ratio of both output components of the television signal.