Signal processing apparatus for eliminating ringing signal and method thereof, record medium, and program

Image quality degrading components can be eliminated from a contour correction signal of high frequency region that is used for contour correction. A filtering section extracts a high frequency region signal from a signal inputted from a VLPF. A mask generating section generates a mask by masking image quality degrading components (e.g., ringing components) contained in the extracted signal. A gain factor generating section generates a gain factor that eliminates image quality degrading components on the basis of the mask. A multiplier multiplies the extracted signal by the gain factor, and outputs an adder a resultant signal (horizontal contour correction signal free from the image quality degrading components). Since the horizontal contour correction signal is generated by eliminating the image quality degrading components from the high frequency region signal, the occurrence of ringing and the like can be suppressed to ensure excellent image quality.

CROSS REFERENCE TO RELATED APPLICATION

This application claims priority from Japanese Priority Document No. 2003-024714, filed on Jan. 31, 2003 with the Japanese Patent Office, which document is hereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a signal processing apparatus and a method, a record medium and a program. More particularly, the invention relates to a signal processing apparatus and a method, a record medium and a program with which it is capable of eliminating properly a ringing component from a contour correction signal.

2. Description of Related Art

FIG. 1shows the configuration of a signal processing apparatus1that processes a video signal from a conventional CCD (charge coupled device) camera, which is discussed in, for example, “Introduction to CCD Camera Technique” by Hiroo Takemura, Corona Publishing Co., Ltd., pp. 144-145.

A VLPF (vertical low pass filter)11performs vertical low pass filtering processing of a video signal (hereinafter referred to as an input video signal) from a CCD camera (not shown), and outputs a resultant signal to a luminance signal generating section12and a contour correction signal generating section13.

The luminance signal generating section12includes, for example, a horizontal LPF and the like, and generates from the signal inputted from the VLPF11a horizontal luminance signal having frequency characteristics as indicated by a dotted line A inFIG. 2.

The contour correction signal generating section13generates from the signal inputted from the VLPF11a horizontal contour correction signal (a high frequency region signal) having frequency characteristics as indicated by a solid line B inFIG. 2, and then outputs this correction signal to an adder14.

FIG. 3shows an example of the configuration of the contour correction signal generating section13.

The signal from the VLPF11is inputted to a delay circuit21and an adding circuit23. The delay circuit21delays the inputted signal for an arbitrary time τ, and then outputs a resultant signal to a delay circuit22and a subtracting circuit25.

The delay circuit22further delays the signal inputted from the delay circuit21for the time τ and then outputs a resultant signal to the adding circuit23.

The adding circuit23adds the signal from the VLPF11and the signal from the delay circuit22, and then outputs a resultant signal to a dividing circuit24.

The dividing circuit24divides the signal inputted from the adding circuit23into halves, and then outputs a resultant signal to the subtracting circuit25. The subtracting circuit25subtracts the signal inputted from the dividing circuit24from the signal inputted from the delay circuit21, and then outputs a resultant signal to the adder14(FIG. 1), as a horizontal contour correction signal.

In the adder14, a luminance signal from the luminance signal generating section12and a horizontal contour correction signal from the contour correction signal generating section13are added, and a resultant signal (luminance signal) is then outputted to the luminance signal processing circuit15.

By adding the horizontal contour correction signal of high frequency region to the luminance signal as described above, the luminance signal once falls temporarily at the time of rise, and then rises, and returns after exceeding a predetermined level, so that it is able to improve sharpness of the entire image.

The luminance signal processing circuit15performs processing, such as adding a synchronizing signal and a blanking signal to the luminance signal inputted from the adder14.

However, the horizontal contour correction signal generated by the conventional contour correction generating section13(FIG. 3) contains image quality degrading components without change (ringing components and the like), as indicated by dotted circles R inFIG. 4. The conventional manner of correcting a luminance signal by a contour correction signal suffers from the problem that ringing occurs in an edge peripheral portion, or aliasing occurs, thus degrading image quality.

Therefore, there is a need for eliminating such image quality degrading components from a contour correction signal of high frequency region thereby to suppress image quality degradation due to ringing and the like.

SUMMARY OF THE INVENTION

A signal processing apparatus of the present invention includes: means for generating a luminance signal of an input video signal; means for extracting a high frequency signal from the input video signal; mask generating means for generating a mask by masking image quality degrading components contained in the high frequency signal; gain factor generating means for generating a gain factor on the basis of the mask; contour correction signal generating means for generating a contour correction signal by multiplying the high frequency signal with the gain factor; and correcting means for correcting the luminance signal on the basis of the contour correction signal.

The mask generating means can generate the mask by repeating an arbitrary number of times dilation processing or erosion processing for the high frequency signal.

There is further provided with detecting means that detects either or both of an edge component and chroma component from an input video signal. The gain factor generating means can generate a gain factor that is based on the mask and controls the enhanced amount of either or both of the edge component and chroma component.

A signal processing method of the present invention includes the steps of: generating a luminance signal of an input video signal; extracting a high frequency signal from the input video signal; generating a mask by masking image quality degrading components contained in the high frequency signal; generating a gain factor on the basis of the mask; generating a contour correction signal by multiplying the high frequency signal by the gain factor; and correcting the luminance signal on the basis of the contour correction signal.

A record medium of the present invention includes stored computer program that comprises the steps of generating a mask by masking image quality degrading components contained in a high frequency signal extracted from an input video signal; generating a gain factor on the basis of the mask; generating a contour correction signal by multiplying the high frequency signal by the gain factor; and correcting a luminance signal of the input video signal on the basis of the contour correction signal.

A program of the present invention has a computer execute processing including the steps of generating a mask by masking an image quality degrading component contained in a high frequency signal extracted from an input video signal; generating a gain factor on the basis of the mask; generating a contour correction signal by multiplying the high frequency signal by the gain factor; and correcting a luminance signal of the input video signal on the basis of the contour correction signal.

In the signal processing apparatus and method, the record medium and the program of the present invention, a luminance signal of an input video signal is generated, and a high frequency signal is extracted from the input video signal. A mask is generated by masking image quality degrading components contained in the high frequency signal. A gain factor is generated on the basis of the mask. A contour correction signal is generated by multiplying the high frequency signal by the gain factor. The luminance signal is corrected on the basis of the contour correction signal.

In accordance with the present invention, it is capable of eliminating properly image quality degrading components from a contour correction signal.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 5shows an example of the configuration of a signal processing apparatus30to which the present invention is applied. The signal processing apparatus30is provided with a contour correction signal generating section31in place of the contour correction signal generating section13of the conventional signal processing apparatus1inFIG. 1. Otherwise, the apparatus30is identical to the apparatus1inFIG. 1, and therefore its description is omitted herein.

FIG. 6shows an example of the configuration of the contour correction signal generating section31.

A filtering section41extracts a high frequency region signal from a signal inputted from a VLPF11(FIG. 5), and then outputs it to a mask generating section42and a multiplier44.

The mask generating section42generates a mask by masking image quality degrading components (ringing components and the like) contained in the high frequency region signal extracted by the filtering section41, and then outputs the mask to a gain factor generating section43.

On the basis of the mask generated by the mask generating section42, the gain factor generating section43generates a gain factor (gain factor C3) for eliminating image quality degrading components and then outputs the gain factor C3to the multiplier44.

The multiplier44multiplies the high frequency region signal extracted by the filtering section41by the gain factor C3supplied from the gain factor generating section43, and then outputs a resultant signal (a horizontal contour correction signal which is free from the image quality degrading components) to an adder14(FIG. 5).

That is, according to the signal processing apparatus30, the horizontal contour correction signal is generated by eliminating the image. quality degrading components from the high frequency region signal. This enables to improve sharpness of the entire image and also ensures excellent image quality while suppressing the occurrence of ringing and the like.

The following is a detail description of the filtering section41. The filtering section41consists of a horizontal BPF (band pass filter)51and a coring section52. Their operations will be described below.

The horizontal BPF51performs horizontal band-pass filtering processing of a signal from the VLPF11, and then outputs a resultant signal to the coring section52. In this case, the filtering factors of the horizontal BPF51are, for example, 0.0125, −0.0625, 0.1375, −0.1875, 0.175, −0.075, 0.175, −0.1875, 0.1375, −0.0625, and 0.0125.

The coring section52performs coring processing based on the following relationships between input and output with respect to a signal (signal G52-in) inputted from the horizontal BPF51, and then outputs a resultant signal (signal G52-out) to the mask generating section42.FIG. 7shows the relationships between input and output.
G52-out=G52-in+LC,whenG52-in<−LC
G52-out=0, when−LC≦LC
G52-out=G52-in−LC,whenG52-in>LC

Thus, by the band-pass filtering processing and coring processing of the signal from the VLPF11, a high frequency region signal is extracted and inputted to the mask generating section42.

The following is a detail description of the mask generating section42(the operation thereof will also be described later). An absolute value processing section61obtains the absolute value of the high frequency region signal from the filtering section41, and then outputs it to a horizontal LPF62. The horizontal LPF62performs horizontal low pass filtering processing of the absolute value signal from the absolute value processing section61, and then outputs a resultant signal to a threshold value processing section63and the gain factor generating section43. The filtering factors of the horizontal LPF62are, for example, 0.25, 0.5, and 0.25.

With use of four threshold values th0to th3, the threshold value processing section63converts the signal (signal G63-in) inputted from the horizontal LPF62to, for example, an index signal (signal G63-out) made up of five stages of value 0 to value 4, as described below.
G63-out=0, whenG63-in<th0
G63-out=1, when th0≦G63-in<th1
G63-out=2, when th1≦G63-in<th2
G63-out=3, when th2≦G63-in<th3
G63-out=4, when th3≦G63-in

The isolated point eliminating section64performs isolated point eliminating processing of the index signal inputted from the threshold value processing section63, and then outputs a resultant signal to a mask processing section65.

Specifically, the isolated point eliminating section64converts the index of a target pixel to value 0, when all the indexes of pixels in a predetermined positional relationship relative to the target pixel (i.e., peripheral pixels) have value 0. The isolated point eliminating section64also converts the index of the target pixel to a maximum value in the indexes of peripheral pixels, when all the indexes of the peripheral pixels have a value other than value 0. In the cases other than that (if there is one or more indexes having value 0, although all the indexes of peripheral pixels do not have value 0), the isolated point eliminating section64leaves the index of a target pixel as it is, without converting.

For example, when two pixels adjacent each other in a horizontal direction with respect to a target pixel P(j, i) are taken as peripheral pixels P(j−1, i) and P(j+1, i), respectively, the index of value 3 of the target pixel P(j, i), as shown on the left side inFIG. 8, is converted to value 0, as shown on the right side inFIG. 8, because both of the indexes of the peripheral pixels P(j−1, i) and P(j+1, i) have value 0. The index of value 2 of a target pixel P(j, i), as shown on the left side inFIG. 9, is converted to a maximum value (value 4) in the indexes of peripheral pixels P(j−1, i) and P(j+1, i), as shown on the right side inFIG. 9, because the indexes of these peripheral pixels have a value (value 3, value 4) other than value 0. The index of value 2 of a target pixel P(j, i), as shown on the left side inFIG. 10, retains its value as shown on the right side inFIG. 10, because there is one peripheral pixel P having an index of value 0. The letters “j” and “i” in the foregoing (j, i) indicate the x coordinate and the y coordinate, respectively.

The index of a target pixel, the value of which is converted or left as it is by the above-mentioned isolated point eliminating processing, is inputted to the mask processing section65(FIG. 6) as an output signal.

Referring toFIG. 11, the mask processing section65in this example consists of one dilation section66and four erosion sections67-1through67-4(hereinafter referred to simply as “erosion section 67”, if there is no need to individually differentiate).

The dilation section66converts the index of a target pixel to a maximum value in the indexes of peripheral pixels, when there is one or more peripheral pixels Q, the index of which is not value 0. Further, the dilation section66leaves the index of a target pixel as it is, without converting, when all the indexes of peripheral pixels have value 0.

For example, the index of value 2 of a target pixel P(j, i) that is shown on the left side inFIG. 12, is converted to a maximum value (value 3) in the indexes of peripheral pixels P(j−1, i) and P(j+1, i), as shown on the right side inFIG. 12, because there is the peripheral pixel P(j−1, i), the index of which is a value 3 other than value 0.

The index of a target pixel, the value of which is converted or retained unchanged by this dilation processing, is inputted to the erosion section67-1.

The erosion sections67-1through67-4convert the index of a target pixel to value 0, when there is one or more peripheral pixels having an index of value 0, and do not convert the index of a target pixel when there is no peripheral pixel having an index of value 0.

For example, the index of value 2 of the target pixel P(j, i) that is shown on the left side inFIG. 13is converted to value 0 that is shown on the right side inFIG. 13, because there is one peripheral pixel having an index of value 0.

The index of the target pixel, the value of which is converted or retained unchanged by this erosion processing, is inputted to the erosion section67of subsequent stage or the gain factor generating section43(FIG. 6).

Thus, to the high frequency region signal extracted by the filtering processing section41, different index signals (masks) both as regards an image quality degrading portion and other portions are generated by the foregoing dilation processing and erosion processing (which are hereinafter generally referred to as “mask processing” in some cases).

The index signal from the mask processing section65of the mask generating section42is inputted to the gain factor generating section43. Here, gain factor generating processing in the gain factor generating section43will be discussed below.

Referring toFIG. 14, the gain factor generating section43first determines a gain factor C1in accordance with a rule corresponding to index EX from the mask generating section42(mask processing section65).

Concretely, when the index EX is value 0 or value 4, the gain factor C1has value 0. When the index EX is value 1, the gain factor C1has a value given by Equation (1). When the index EX is value 3, the gain factor C1has a value given by Equation (2).
C1=(G43-in−thresholdth0)/(thresholdth1−thresholdth0)   (1)
C1=1−(G43-in−thresholdth2)/(thresholdth3−thresholdth2)   (2)
where G43-in is a signal inputted from the horizontal LPF62to the gain factor generating section43, and thresholds th0through th3are the same threshold value as used in the threshold value processing section63.

The gain factor generating section43multiplies the gain factor C1so determined by a predetermined intensity factor C2that is variable by a user, thereby generating a gain factor C3. That is, when index EX is a large value (e.g., value 4) or a small value (e.g., value 0) and expected as an image quality degrading component, the gain factor C3has a small value (e.g., value 0). Therefore, multiplying in the multiplier44a high frequency region signal extracted in the filtering section41by the gain factor C3enables to suppress (eliminate) the image quality degrading components of the high frequency region signal.

Next, the operation of the filtering section41, mask generating section42and gain factor generating section43will be described with reference toFIG. 15toFIG. 22.

A signal from the VLPF11as shown inFIG. 15is subjected to horizontal band-pass filtering processing by the horizontal BPF51of the filtering section41, and then converted to such a signal as shown inFIG. 16, and thereafter inputted to the coring section52. A signal shown inFIG. 17that is obtained by coring processing, namely, a high frequency region signal, is inputted to the mask generating section42and multiplier44. This high frequency region signal contains image quality degrading components that are indicated by dotted circles R inFIG. 17. It is however capable of eliminating the image quality degrading components by generating the gain factor C3depending on a mask generated by the mask generating section42, and multiplying the high frequency region signal by the gain factor C3.

The signal (FIG. 17) inputted to the absolute value processing section61of the mask generating section42is converted there to a signal of an absolute value (FIG. 18), and then inputted to the horizontal LPF62. Signal (FIG. 19) after being subjected to horizontal low pass filtering processing by the horizontal LPF62is inputted to the threshold value processing section63and gain factor generating section43.

The threshold value processing section63compares the level of the signal (FIG. 19) inputted from the horizontal LPF62with four threshold values th0through th3, as shown inFIG. 20A, and then converts it to an index signal made up of value 0 through value 4 (FIG. 20B). Note that index signals shown inFIGS. 20A to 20Ghave value 0 to value 2.

The index signal from the threshold value processing section63is subjected to isolated point elimination by the isolated point eliminating section64, and then inputted to the mask processing section65where mask processing is performed. For example, the index signal shown inFIG. 20Bis converted to that shown inFIG. 20Cby dilation processing in the dilation section66of the mask generating section65, followed by sequential erosion processing in the four erosion sections67-1through67-4. As a result, the index signal is converted sequentially to the index signals shown inFIG. 20DthroughFIG. 20G.

The signal resulting from the processing in the mask processing section65(i.e., the signal from the erosion section67-4) (FIG. 20G) is inputted to the gain factor generating section43.

The gain factor generating section43determines the gain factor C1in accordance with a rule corresponding to an index from the mask processing section65(FIG. 14, Equation (1), Equation (2)). From the index signal (mask) shown inFIG. 21B(=FIG. 20G), the gain factor C1shown inFIG. 21Cis found.FIG. 21A(=FIG. 19) illustrates the signal G43-in that is inputted from the horizontal LPF62to the gain factor generating section43.

The gain factor generating section43calculates the gain factor C3by multiplying the gain factor C1shown inFIG. 21Cby the intensity factor C2set by a user, and then outputs the gain factor C3to the multiplier44. Specifically, the multiplier44multiplies a high frequency region signal extracted by the filtering section41shown inFIG. 22A(=FIG. 17) by the gain factor C3that is obtained by multiplying the gain factor C1inFIG. 22B(=FIG. 21C) by the intensity factor C2. This provides a high frequency region signal (horizontal contour correction signal) from which image quality degrading components (the portions indicated by the dotted circles R inFIG. 17) are eliminated, as shown inFIG. 22C.

Although in the foregoing the mask processing section65consists of one dilation section66and four erosion sections67, the number of the dilation section66and erosion section67may be changed selectively depending on the video complexity in an input video image and the like.

FIG. 23illustrates another example of the configuration of the signal processing apparatus30, which is provided with a contour correction signal generating section71in place of the contour correction signal generating section31inFIG. 5. To the contour correction signal generating section71, an input video signal is inputted together with the signal from the VLPF11.

FIG. 24illustrates an example of the configuration of the contour correction signal generating section71, in which an edge detecting section81is added to the contour correction signal generating section31inFIG. 6.

An input video signal from a CCD camera is inputted to a horizontal LPF91of the edge detecting section81. The horizontal LPF91performs horizontal low pass filtering processing of the input video signal and then outputs a resultant signal to a difference detecting section92. The filtering factors of the horizontal LPF91are, for example, 0.5, and 0.5.

The difference detecting section92detects a horizontal difference value from a signal inputted from the horizontal LPF91, and then outputs an adjacent search section93a value (a comparison result DR) that is based on a comparison result between the difference value and a predetermined threshold value.

Concretely, as shown inFIG. 25, the following difference values d0, d1, and d2are calculated with respect to two peripheral pixels P(j−1, i) and P(j+1, i) that are adjacent each other in a horizontal direction relative to the target pixel P(j, i).
Difference valued0=Pixel value of target pixelP(j, i)−Pixel value of peripheral pixelP(j−1, i)
Difference valued1=Pixel value of target pixelP(j, i)−Pixel value of peripheral pixelP(j−1,i)
Difference valued2=Pixel value of peripheral pixelP(j−1,i)−Pixel value of peripheral pixelP(j+1,i)

The difference detecting section92outputs value 1 as a comparison result DR(j, i) in the target pixel P(j, i), when one or more of the calculated difference values d0through d2are greater than a predetermined threshold value et (i.e., when any edge is expected to exist). Conversely, the difference detecting section92outputs value 0 when every difference value d is not more than the predetermined threshold value et (i.e., when any edge is not expected to exist).

The adjacent search section93judges whether an edge exists or not in a predetermined region containing the target pixel, by use of the comparison result DR from the difference detecting section92. The adjacent search section93outputs the gain factor generating section43value 0 as a search result RR when the judgment result is that there is an edge, and outputs value 1 as the search result RR when the judgment result is that there is no edge.

It is now proposed to consider a specific example that the comparison result DR(j−1, i) of the pixel P(j−1, i), the comparison result DR(j, i) of the pixel P(j, i), and the comparison result DR(j+1, i) of the pixel P(j+1, i) supplied from the difference detecting section92are taken as one region, as shown inFIG. 26, and when one or more comparison results DR having value 1 exist in these comparison results DR (i.e., when any edge is expected to exist in that region), value 0 is outputted as an adjacent search result RR of the target pixel P(j, i). Conversely, when all the comparison results DR in that region have value 0 (i.e., when no edge is expected to exist in that region), value 1 is outputted as the adjacent search result RR of the target pixel P(j, i).

The gain factor generating section43determines the gain factor C1in accordance with a rule corresponding to the index signal from the mask generating section42(FIG. 14, Equation (1), Equation (2)), and also calculates the gain factor C3by multiplying the gain factor C1, the intensity factor C2, and an output from the edge detecting section81(i.e., the adjacent search result RR). That is, when an edge exists in a predetermined region containing the target pixel P(j, i), the adjacent search result RR has value 0, and therefore the gain factor C3is value 0. As the result, the enhancement intensity of an edge peripheral portion becomes zero, thereby suppressing ringing that occurs in the edge peripheral portion.

FIG. 27illustrates other example of the configuration of the contour correction signal generating section71inFIG. 23, in which a chroma detecting section101is added to the contour correction signal generating section31inFIG. 6.

The chroma detecting section101detects chroma components from an input video signal that is inputted from a CCD camera.

The chroma detecting section101then outputs the gain factor generating section43a maximum value in the calculated difference values d, as a chroma component of the target pixel P(j, i).

The gain factor generating section43detects a gain factor CG, as shown inFIG. 29, which corresponds to the magnitude of the chroma component inputted from the chroma detecting section101. That is, the gain factor CG has a small value when the chroma component is large (when a video image is of chromatic color portion), and has a great value when the chroma component is small (when the video image is of achromatic color portion).

The gain factor generating section43determines a gain factor C1in accordance with a rule corresponding to an index from the mask generating section42(FIG. 14, Equation (1), Equation (2)), and also calculates the gain factor C3by multiplying the gain factor C1, the intensity factor C2, and the gain factor CG. That is, since the gain factor C3regarding the achromatic color portion is allowed to have a great value, the achromatic color portion having a high horizontal resolution can be generated at a high resolution.

FIG. 30illustrate another example of the configuration of the contour correction signal generating section71inFIG. 23, in which the edge detecting section81shown inFIG. 24and the chroma detecting section101shown inFIG. 27are added to the contour correction signal generating section31inFIG. 6.

Specifically, the gain factor generating section43determines the gain factor C1in accordance with a rule corresponding to an index signal from the mask generating section42, and also calculates the gain factor C3by multiplying the gain factor C1, the intensity factor C2, an adjacent search result RR from the edge detecting section81, and the gain factor CG. This case therefore suppresses ringing that occurs in an edge peripheral portion and also generates an achromatic color portion at a high resolution.

The foregoing sequence of processing can be implemented by hardware, as well as software. In the case of implementing the sequence of processing by software, a program constituting the software is installed on a computer, and the program is executed on the computer, so that the above-mentioned processing is implemented functionally.

FIG. 31is a block diagram showing the configuration of one preferred embodiment of a computer functioning as the above-mentioned horizontal contour correction signal generating sections31,71. An I/O (input/output) interface116is connected via a bus15to a CPU (center processing unit)111. When a user inputs an instruction through an input section118made up of a keyboard, mouse and the like to the CPU111via the I/O interface116, the CPU loads on a RAM (random access memory)113a program stored in a record medium such as a magnetic disk131, optical disk132, magneto-optical disk133, or semiconductor memory134, which is mounted on a ROM (read only memory)112, hard disk114, or drive120, and then executes the program to perform a variety of processing as described above. The CPU111also outputs the processing results as required, via the I/O interface116, to an output section117made up of an LCD (liquid crystal display). In an alternative, a program may be previously stored in the hard disk114or ROM112, in order to provide users with the program integrally with the computer101. In other alternative, the program may be provided as package media of the magnetic disk131, optical disk132, magneto-optical disk133, or semiconductor memory134. In still other alternative, the program may be provided to the hard disk114via a communication section119from a satellite, network or the like.

In the present specification, the step of describing a program supplied from a record medium may of course include processing executed in time series in the order described, also include processing that is not always executed in time series and may be executed in parallel or separately.