JP2513752B2 - Television signal scan converter - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a television signal scan converter, and more particularly to a progressive scan signal or a 2: 1 interlace signal having a different number of scan lines to scan a 2: 1 interlace signal. The present invention relates to space-time band limitation of a converter for conversion.

(Summary of the Invention) The present invention relates to a spatio-temporal band limitation processing of an input signal prior to conversion of a sequential interlaced scan converter or a scanning line number converter of a television signal, the converter being a still image filter control means. At least one of the moving picture filter control means is provided, and both control means are provided with two types of low-pass filters each having a different pass band, and the respective two output signals from the two types of filters are mixed. The ratio is controlled by the amount of vertical spatial frequency components in each predetermined band.

As a result, the optimum conditions of the sharpness of the converted image and the folding component are adaptively obtained.

(Prior Art) Conventionally, motion adaptive scanning using fixed filters for still images and moving images as space-time band limitation when converting progressive scan signals or 2: 1 interlace signals with different scanning lines into interlace signals. There was a converter.

(Problems to be Solved by the Invention) In a sequential interlace scanning 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. From scan conversion. In a conventional converter, this band limitation is a motion adaptive process, and a fixed space-time filter is applied to each of a still image and a moving image. However, with this method, the band of the vertical spatial frequency becomes 1/2 and the resolution deteriorates especially for moving images. Further, due to the incompleteness of the filter, the image quality may be unsightly due to the aliasing component after conversion depending on the image even in the half band. In order to prevent this, if the moving image filter is made narrower, the resolution of other moving images is further deteriorated.

Therefore, an object of the present invention is to eliminate the above-mentioned drawbacks and to provide a television signal scan converter capable of optimizing the trade-off between the resolution after conversion and the aliasing component.

(Means for Solving the Problems) In order to achieve this object, a television signal scan converter according to the present invention uses a television progressive scan signal or a 2: 1 interlace scan signal having a different number of scan lines to perform a 2: 1 interlace scan. In a scan converter for performing space-time band limiting processing of an input signal prior to conversion into a signal, the converter is provided with 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 still image low-pass filters of a wide band and a narrow band with respect to vertical spatial frequencies as filters for band limiting the still image, and a vertical high frequency component of the vertical spatial frequency of the input signal. Means for controlling the mixing ratio of both output components of the two low-pass filters for still images according to the amount of The filter control means is provided with two low pass filters for moving images of a wide band and a narrow band with respect to the vertical spatial frequency as a filter for limiting the band of the moving image, and 2 according to the amount of the vertical mid-range component of the vertical spatial frequency of the input signal. It is a means for controlling the mixing ratio of both output components of the one moving picture low-pass filter.

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

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

In FIG. 1, an input signal is led to field (F) memories 1 and 2 connected in cascade. Here, the input signal, the output of the F memory 1 and the output of the F memory 2 are referred to as signals f ₁ , f ₀ and f _-1 , respectively, in the sense of distinguishing the time (field). These signals are first guided to the coefficient multipliers 3, 4 and 5 and multiplied by the coefficients 1/4, 1/2 and 1/4, respectively. The signals of these results are added by the adder 6. These blocks 3-6
Constitutes a time filter 7 which is a band limiting filter for a still image as a whole. The signal f ₀ is also input to the vertical filters 9 and 10. The vertical filters 9 and 10 are in-field vertical spatial filters having no attenuation characteristic in the time direction,
The specific structure can be realized by the second illustrated structure, for example. In FIG. 2, 1-line (H) delay devices 31 to 36 are connected in a cascade, and coefficient multipliers 37 to 43 are provided at the filter input signal and the output tap of each H delay device. Value of each coefficient α _{3 to} α _-3
Determines the spatial frequency characteristic in the vertical direction. Next, the outputs of the coefficient units 37 to 43 are added in the adder 44 to form a filter output signal. These are 7-tap vertical filters, and the filter output signal is delayed by 3H with respect to the input signal.

The outputs of the vertical filters 9 and 10 in the first configuration diagram are mixers 11
They are mixed according to a control signal described later in 1. and become the driving side input of the switch 12. The output of the still image and the filter 7 is
It is led to the static side input of the switch 12 via an n ₁ H (n ₁ is an integer) delay device for delay adjustment with the vertical filters 9 and 10. The value of the integer n ₁ is n ₁ = 3 when the vertical filters 9 and 10 having the second configuration are used, for example. The switch 12 switches between two inputs according to the motion signal output from the motion detection circuit 14. The motion detection circuit is a signal by a known technique.
It is possible to realize f ₁ , f ₀ and f _-1 as input signals. The output of the switch 12 is scan-converted by the scan conversion circuit 13 and becomes a 2: 1 interlaced scan output signal.

On the other hand, the subtracter 15 _obtains the difference signal between the signals f ₁ and f ₋₁ . The difference signal and the signal f ₀ are switched by the switch 16. This operation will be described later in detail.

The output of the switch 16 becomes the input of the n ₂ H (n ₂ is an integer) delay device 17. This delay device is for adjusting the control signal and the delay of the vertical filters 9 and 10 which will be described later, and when using the vertical filter having the second configuration shown in the drawing, n ₂ = 3-2 =
It becomes 1. The output of the n ₂ H delay device 17 is guided to the 2H delay devices 18 and 19 connected in cascade, and the outputs of the delay devices 17 to 19 are respectively coefficient devices 20, 21 and 22 and the coefficient −1/4, 1/1, respectively. It is multiplied by 2, -1 / 4. The results are added by the adder 23 and are input to the absolute value circuit (ABS) 24. These blocks 18 to 23 form a vertical mid-pass filter whose pass band is the mid-frequency component of the vertical spatial frequency.

The characteristic of the absolute value circuit 24 is, for example, the characteristic shown in FIG. A certain dead zone is set for the input level,
For higher levels, it outputs an output level that is linear to the absolute value of the input. At this time, a non-linear level conversion may be performed so that the output image quality of the present apparatus becomes optimum with respect to the absolute value of the input, as indicated by the dotted line. 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. The mixer 11 is, for example, on the vertical filter 9 side when the level of the control signal is low, and when it is high
Set the output point on the 10 side. In this case, the vertical filter 9 is used as a moving image wide band filter, and the vertical filter 10 is used as a moving image narrow band filter.

Next, the difference between the conventional example (FIG. 4) and the scan converter of the present invention (FIG. 5) will be sequentially described using the band characteristic examples shown in FIG. 4 and FIG.

FIG. 4A shows band limitation in the spatio-temporal frequency domain in the conventional scan converter from progressive scanning to interlaced scanning.
In the figure, the horizontal axis is the time frequency f (Hz), the vertical axis is the vertical spatial frequency ν (cycle), and the signal is 1125 scanning lines.
It is assumed that the signal has a field frequency of 60 Hz. Conventionally, as shown in the same figure, for still images, the time frequency (f) direction,
For moving images, band limitation is performed only in the vertical spatial frequency (ν) direction, and the area of both is ν = 1125/2 or less and 1/2 of the region of f = 30 Hz or less. By doing so, it is possible to prevent the aliasing component based on the interlaced scanning after being converted into the interlaced signal from being visually low frequency and the crosstalk between the original component and the aliasing component. This state can be understood from FIG. 4 (b) showing the spectrum of the interlaced signal obtained by converting the still image and FIG. 4 (c) showing the spectrum of the signal obtained by converting the moving image. C _{i in} both figures is a sampling carrier based on interlaced scanning. 4 (b) and 4 (c), the still image band limitation has a higher vertical spatial resolution than the moving image band limitation.
Since it has an attenuation characteristic in the time-frequency direction, blurring, double images, etc. occur in moving images. For this reason, the 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.

Since the band limitation for moving images does not have an attenuation characteristic in the time direction, it can be realized by an interfield vertical filter, but the characteristic is usually imperfect due to the limitation of hardware. For example, in the case of a filter configuration of about 7 taps as shown in FIG. 2, its characteristic is as shown in FIG. 4 (d). For this type of characteristic ν = 1125/4
The response is lowered even below, and if this characteristic is used, the vertical spatial resolution of the moving image is unsatisfactory. Further, the aliasing component shown by the slanted lines in FIG. 4 (d) extends to a reduction of ν = 1125/4 or less, so that the aliasing component becomes noticeable as an interference component in some images.

FIG. 5A shows a characteristic example of band limitation by the scan converter of the present invention. The conditions in the figure are the same as the conditions in FIG. In FIG. 5 (a), the band limitation for a still image is the same as that in FIG. 4 (a), but the band limitation for a moving image includes motion 1 and motion 2, and the motion 1 has a pass band of v = 1125 / It has a broadband characteristic of 4 or more, and a dynamic bandwidth 2 of ν = 1125/4 or less. When a signal whose band is limited by the characteristic of motion 1 is converted into an interlaced signal, a signal having a spectrum as shown in FIGS. According to this characteristic, as shown in the figure, the folding component extends to the low frequency range and a large crosstalk occurs with the original component, but the original component is hardly attenuated up to about ν = 1125/4, and a good vertical spatial resolution is obtained. Have Therefore, if the amount of the folding component is within the visually permissible range, a moving image with good sharpness can be obtained by using this characteristic. On the other hand, if a signal whose band is limited by the characteristic of motion 2 is converted into an interlaced signal, a signal having a spectrum as shown in FIGS. With this characteristic, the band of the original component is also narrowed, but the aliasing component hardly appears below ν = 1125/4. Although the converted image quality based on this characteristic is slightly poor in sharpness, there is no interference with the image quality due to the folding component.

To the human eye, when the image quality disturbance exceeds the permissible limit, it is felt as the image quality deterioration is larger than the poor sharpness.
When the folding component is large, it is preferable in terms of image quality to use the characteristic of motion 2. In the circuit of FIG. 1, the control signal for switching the band of the vertical filter by detecting the amount of the component of the area A or the area B of the characteristic shown in FIG. 5 (f) by the switch 16 is used. In FIG. 1, when the switch 16 is tilted to the C side, the component of the area A is detected, and when it is tilted to the D side, the component of the area B in which the band limitation is further applied to the area A in the time direction is detected. Area A, B
Both have characteristics as shown in FIG. 5 (g) in the vertical direction, and are in the middle range at the vertical spatial frequency. It is understood that the region A is a region where there is a difference in the characteristics of the motion 1 and the motion 2, and the switching of the motion 1 and the motion 2 can be performed by detecting the component of this region and controlling the amount to be an appropriate amount. In this case block 17
Instead of using the circuit of 23 to 23, the difference between the output signals of the vertical filters 9 and 10 may be input to the ABS 24. However, there is a possibility that it is better to detect the component from the region B, which is a region of a moving image that is purely a component of a moving image and is a region where aliasing is noticeable after scan conversion, in the region A. . This switching may be determined by comprehensively looking at the converted image quality.

FIG. 6 is a block diagram showing the configuration of another embodiment of the scan converter of the present invention. In addition to the function of the circuit of the first configuration shown, the circuit of this configuration is also adapted to switch the characteristics for still images in accordance with the input signal. In FIG. 6, band limitation for still images is performed by the spatiotemporal filters 53 and 54. Filter 53,
Reference numeral 54 is a filter that performs band limitation not only in the time direction but also in the vertical direction like the time filter 7 shown in the first figure.
It can be realized by a known technique using the signals f ₁ , f ₀ and f _-1 as inputs.
The outputs of the filters 53 and 54 are mixed by the mixer 57 according to the control signal 2 and become the static side input of the switch 59. The control signal 2 is generated by a circuit similar to the blocks 17 to 24 of the first illustrated configuration, based on the result of detecting the amount of the vertical high frequency component of the signal f ₀ by the vertical high frequency detection circuit 63. Other circuits of the configuration shown in FIG. 6 are similar to the corresponding circuits of FIG.

FIG. 7 (a) shows an example of characteristics used in the space-time filter for still images of FIG. The static 1 is the same as the characteristic for a still image in FIG. 4, and the static 2 is the characteristic of the static 1 further band-limited in the ν direction. Switching between the two is performed according to the amount of the component of the region X which is the vertical high frequency component. When a signal band-limited by the characteristics of static 2 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 the still image is less than that of the still image 1, but the component of the region Y in the figure does not occur as the folding component. The region Y is a component that is noticeable as an 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 is applicable to, for example, 52
It can also be used for 5 signals. Further, not only the sequential interlace converter, but also a scanning line number converter for converting from 1125 scanning lines to 525 lines or 625 scanning lines, for example.

Furthermore, in the embodiment of the present invention, a motion detection circuit is provided to perform a motion adaptive type process for switching between a still image and a moving image, but this process is not absolutely necessary in the present invention.

Further, in the other embodiment of the present invention, both the switching of the filters of dynamic 1 and dynamic 2 and the switching of the filters of static 1 and static 2 are used, but the object of the present invention can be achieved by either one.

(Effects of the Invention) As described in detail above, if the television signal scan converter of the present invention is used, it is possible to respond to a signal component of a television input image of sequential scanning or interlaced scanning with different scanning lines. The trade-off between the resolution of the 2: 1 interlaced scan image after scan conversion and the aliasing component can be optimally processed, and the image quality after conversion can be improved.

[Brief description of drawings]

FIG. 1 shows a block diagram of the construction of an embodiment of the scan converter of the present invention, and FIGS. 2 and 3 show a construction example of a vertical filter and an absolute value circuit used in the converter having the construction shown in FIG. Characteristic examples are shown respectively, and FIGS. 4 (a) to (d) and FIGS. 5 (a) to (g) show
FIGS. 6A and 6B are diagrams for explaining the band limitation in the conventional converter and the converter of the present invention, respectively, FIG. 6 is a block diagram of the configuration of another embodiment of the present invention, and FIGS. FIG. 16 is a diagram showing an example of band limitation in the sixth illustrated embodiment. 1,2,51,52 …… Field memory (F) 3 to 5,20 to 22,37 to 43 …… Each coefficient unit 6,23,44 …… Adder 7 …… Band limit time filter 8,17, 18,19,31 to 36 …… Delay device 9,10,55,56 …… Vertical filter 11,57,58 …… Mixer 12,16,59 …… Selection switch 13,60 …… Scan conversion circuit 14 , 61 …… Motion detection circuit 15 …… Subtractor 24 …… Absolute value circuit (ABS) 53,54 …… Spatiotemporal filter 62 …… Vertical mid-range detection circuit 63 …… Vertical high-range detection circuit

Claims (1)

(57) [Claims] 1. A scan conversion for performing space-time band limitation processing of an input signal prior to conversion when scan-converting a television progressive scan signal or a 2: 1 interlace scan signal having a different number of scan lines into a 2: 1 interlace scan signal. In the converter, the converter is provided with at least one of a still picture filter control means and a moving picture filter control means, and the still picture filter control means is a filter for performing band limitation on a still picture with respect to a vertical spatial frequency. Equipped with two low-pass filters for wideband and narrowband still images,
Means for controlling the mixing ratio of both output components of the two low-pass filters for still images according to the amount of vertical high-pass components of the vertical spatial frequency of the input signal, wherein the moving-image filter control unit is a band for moving images. As a filter for limiting, two low-pass filters for a moving image having a wide band and a narrow band with respect to a vertical spatial frequency are provided, and the two low-pass filters for a moving image according to the amount of a vertical mid-range component of the vertical spatial frequency of the input signal. 2. A television signal scan converter characterized in that it is means for controlling a mixing ratio of both output components.