JP2004208038A - Apparatus and method of processing image, and apparatus and method of picking up image employing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To enable contour correction of a still image, which is capable of suppressing the generation of a black edge due to undershoot in a contour section while improving a resolution feeling. <P>SOLUTION: A digital image signal S<SB>1</SB>from an input terminal 6 is subjected to contour correction in which undershoot and overshoot are added in a contour correcting means 5, and then, is supplied to a selecting means 5. Also, this signal S<SB>1</SB>is supplied to an edge detecting means 2 to detect its edge period. In an edge generating means 3, an edge signal SE is generated on the basis of the detected edge period, the signal S<SB>1</SB>and an edge coefficient K, and the generated signal is mixed with a digital image signal S<SB>2</SB>outputted from a contour correcting means 1 at a predetermined ratio. In this way, a digital image signal S<SB>3</SB>having undershoot suppressed during the edge period is obtained. During the edge period of the signal S<SB>2</SB>from the means 1, the means 5 replaces the signal S<SB>2</SB>with a digital image signal S<SB>E</SB>from a mixing means 4. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an image signal processing apparatus and method, and an imaging apparatus and method using the same, and more particularly, to an image signal processing apparatus and method for correcting the contour of an image, and an imaging apparatus and method using the same.
[0002]
[Prior art]
As a method for increasing the resolution of an image, for example, in the case of an imaging apparatus, in order to correct the deterioration of the frequency characteristics due to the aperture of the imaging element, a contour correction signal consisting of a horizontal or vertical preshoot and overshoot is used from the image signal. A method is known in which the resolution is increased by generating and adding this to the original image signal (see, for example, Patent Document 1 or Patent Document 2).
[0003]
FIG. 2 is a block diagram showing a conventional example of a contour correction circuit used in an image signal processing apparatus, wherein 1 is a contour correction circuit, 1a is a contour correction signal generation unit, 1b is a gain adjustment unit, 1c is an addition unit, 1d is an input terminal and 1e is an output terminal.
[0004]
FIG. 3 is a waveform diagram showing signals at various parts in FIG. 2, and the signals corresponding to those in FIG.
[0005]
2 and 3, the digital image signal a input from the input terminal 1d is supplied to the adder 1c and the contour correction signal generator 1a in the contour correction circuit 1. Here, FIG. 3A shows a portion (rising edge, falling edge portion) where the contour of the digital image signal a exists.
[0006]
In the contour correction signal generation unit 1a, the high frequency component of the digital image signal a is extracted, and preshoot and overshoot as shown in FIG. 3 (b) synchronized with the contour portion of the digital image signal a from the high frequency component. A contour correction signal b is generated. After the gain is adjusted by the gain adjusting unit 1b, the contour correction signal b is supplied to the adding unit 1c and added to the original digital image signal a input from the input terminal 1d. As a result, in the output terminal 1e, the digital image signal in which the contour portion is emphasized and corrected by undershooting on the low luminance level side and overshooting on the high luminance level side in the contour portion of the original digital image signal a. c is obtained.
[0007]
According to such contour correction processing, the conventional digital image signal processing apparatus mainly handling moving images has the effect of improving the image resolution and improving the image quality.
[0008]
By the way, the purpose of contour correction is to increase the slope of the edge, and undershoot and overshoot are not ideal, and techniques for reducing these overshoot and undershoot have been proposed. (For example, refer to Patent Document 3).
[0009]
In the same manner as described above, when a contour correction signal including an undershoot and an overshoot is generated, the time width of the undershoot and the overshoot is shortened by passing the signal through the switch means. The contour correction signal processed in this way is added to the original image signal.
[0010]
[Patent Document 1]
JP 58-38074 A
[0011]
[Patent Document 2]
JP-A-3-29578
[0012]
[Patent Document 3]
JP-A-5-316393
[0013]
[Problems to be solved by the invention]
Incidentally, in recent years, image signal processing apparatuses that handle still images have become widespread. For example, a digital still camera that records a photographed image on a recording medium such as a memory, a printer connected to a personal computer, a scanner main body or driver software, and image processing software for a personal computer.
[0014]
However, when the conventional contour correction processing described with reference to FIGS. 2 and 3 is performed by an image signal processing apparatus that handles still images, particularly in the edge portion where the difference in the luminance level of the still image is large, the lower luminance level side. The undershoot d shown in FIG. 3 makes a black edge appear, and this black edge becomes very conspicuous.
[0015]
On the other hand, as described in Patent Document 3, a technique has been proposed in which the time width of undershoot and overshoot in the generated contour correction signal is reduced and the influence of these is reduced during contour correction. However, with such a technique, even if the time width of undershoot or overshoot is reduced, the signal level of these undershoots and overshoots remains, so the black edges caused by undershoot are simply narrowed. It's just a black edge.
[0016]
In addition, the techniques described in any of the above-mentioned patent documents can only obtain the contour correction effect by the generated contour correction signal, and in the case of a still image, further improvement of the contour correction is desired.
[0017]
An object of the present invention is to perform contour correction processing that solves such a problem and can effectively suppress the occurrence of black edges at the contour portion while sharpening the contour portion even for a still image. An object of the present invention is to provide an image signal processing apparatus and method, and an imaging apparatus and method using the same.
[0018]
[Means for Solving the Problems]
To achieve the above object, the present invention provides an image signal processing apparatus having a plurality of contour correction means for performing contour correction processing on an input digital image signal and a selection means for selecting one of the plurality of contour correction means. The predetermined contour correcting means among the plurality of contour correcting means includes contour correcting means for detecting the contour of the input digital image signal and contour correcting means other than the predetermined contour correcting means. And a contour correcting unit that corrects the contour of the digital image signal. The selecting unit selects the digital image signal output from the adding unit when the contour detecting unit detects the contour period. Is.
[0019]
Contour correction means other than the predetermined contour correction means perform contour correction by causing undershoot and overshoot in the contour portion of the input digital image signal.
[0020]
The contour correction means includes a contour correction signal generation means for generating a contour correction signal in accordance with the contour portion of the input digital image signal, and a contour correction means other than the contour correction signal and the predetermined contour correction means. The corrected digital image signal is mixed at a predetermined ratio and mixed means for suppressing the undershoot of the contour-corrected digital image signal.
[0021]
The contour detection unit determines whether the detected contour is a rising contour or a falling contour, and when the detected contour is a falling contour, delays the detection timing of the contour period and corrects the contour The signal generator generates the generated contour correction signal in accordance with the contour period detected by the contour detector.
[0022]
The contour detecting means is a first means that considers a flat part of the image when the fluctuation of the digital image signal is within a preset threshold value range, and a slope between the two flats detected by the first means. When the absolute value of the difference between the signal levels on the slope is larger than a preset threshold value, the second means for considering the space between these two flat portions as the contour portion of the digital image signal, It is what has.
[0023]
The contour detection means includes a first means that considers the image flat when the fluctuation of the digital image signal is within a preset threshold range, and a slope where the fluctuation of the digital image signal sequentially increases or decreases. A second means that regards the mutation point moving to the descending or rising slope as the top of the mountain or the bottom of the valley, the flat part detected by the first means, and the mutation point detected by the second means When the absolute value of the signal level difference between them is larger than a preset threshold value, there is provided a third means for regarding the area between the flat portion and the variation point as the contour portion of the digital image signal.
[0024]
Further, the contour detection means regards the first variation point at which the fluctuation of the digital image signal is shifted from the rising or falling slope to the falling or rising slope as the top of the mountain or the bottom of the valley, and this first variation. A first means for setting a second mutation point that rises or descends sequentially after a slope that descends or rises sequentially from the point to the bottom of the valley or the top of the mountain, and the first and first detected by the first means And a third means for regarding the difference between the first and second mutation points as a contour portion of the digital image signal when the absolute value of the signal level difference between the two mutation points is larger than a preset threshold value. Is.
[0025]
In order to achieve the above object, the present invention provides an image pickup means for picking up an image of a subject and outputting an electric signal, and a signal processing means for processing the electric signal output from the image pickup means to generate a first digital image signal. And an image signal processing means for correcting the contour of the first digital image signal, wherein any one of the image signal processing apparatuses described above is used as the image signal processing means. Is.
[0026]
In order to achieve the above object, the present invention is an image signal processing method, comprising: a first digital image signal obtained by contour-enhancing an input digital image signal and contour enhancement; and enhancement of the first image signal. A second digital image signal that suppresses undershoot in the contoured portion is generated, the second digital image signal is selected in the contour portion period, and the first digital signal is selected in a period other than the contour portion period. Is selected and output.
[0027]
In order to achieve the above object, the present invention provides an imaging method for obtaining a digital image signal by performing signal processing on an image signal obtained from a photographing means, and correcting the contour of the digital image signal. Correction processing is performed using the image signal processing method described above.
[0028]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the drawings.
[0029]
FIG. 1 is a block diagram showing an embodiment of an image signal processing apparatus and method according to the present invention, wherein 1 is a contour correcting means, 2 is an edge (contour portion) detecting means, and 3 is an edge (contour correcting signal) generating means. Reference numeral 4 denotes mixing means, 5 denotes selection means, 6 denotes an input terminal, 7 denotes an output terminal, and 8 denotes contour correction means.
[0030]
In the figure, the digital image signal S inputted from the input terminal 6 is shown. ₁ Is supplied to the contour correction means 1 and 8. The contour correction means 1 has the same configuration as that of the conventional digital image signal processing apparatus shown in FIG. 2, performs the same operation, and performs a digital image signal S subjected to contour correction processing in the same manner as the digital image signal c shown in FIG. ₂ Is output. This digital image signal S ₂ Is supplied to the selection means 5 and the mixing means 4.
[0031]
On the other hand, the contour correcting means 8 is constituted by an edge detecting means 2, an edge generating means 3 and a mixing means 4, and a digital image signal S from an input terminal 6 is obtained. ₁ Is supplied to the edge detection means 2 and the edge generation means 3.
[0032]
The edge detection means 2 receives the input digital image signal S by a method described later. ₁ When the edge (contour part) of the digital image signal signal S is detected, the edge generation unit 3 detects the digital image signal signal S based on the detection result. ₂ And an edge coefficient K supplied from an interpolation control means (not shown) _E Is generated. This edge signal S _E Is supplied to the mixing unit 4 and output from the contour correcting unit 1. ₂ Mixed with. The edge signal S _E In this way, the digital image signal S ₂ As will be described later, this is a contour correction signal for suppressing undershoot in the contour portion caused by the correction processing by the contour correction means 1, and will be expressed as an edge signal hereinafter. As described above, the edge generating means 3 and the mixing means 4 are connected to the digital image signal S subjected to the interpolation process from the contour correcting means 1. ₂ Edge correction means for suppressing undershoot occurring in the first is formed.
[0033]
The edge signal S output from the mixing means 4 _E A digital image signal S mixed with _Three Is supplied to the selection means 5. The selection means 5 is such that the edge detection means 2 is digital image signal S. ₁ This edge period selection control signal S generated when the edge of the edge is detected _S In the edge period, the output digital image signal S3 of the mixing unit 4 is selected, and in the period other than the edge period, the output digital image signal S of the contour correcting unit 1 is selected. ₂ Select. As a result, the output digital image signal S of the contour correcting means 1 is applied to the output terminal 7. ₂ Is the output digital image signal S of the mixing means 4 during the edge period. _Three Is obtained by interpolation.
[0034]
Next, the operation of the edge detection means 2 will be described with reference to FIGS.
[0035]
FIG. 4 is a flowchart showing a specific example of the edge detection operation of the edge detection means 2. This edge determination is performed using three threshold values DELTA1, DELTA2, and LEVEL for a plurality of sample periods (hereinafter referred to as determination sample periods), and DELTA1 <DELTA2 and DELTA1 <LEVEL. The determination sample period is set to such an extent that a striped pattern edge that repeats with a minimum period on the image can be determined. Here, the threshold value DELTA 1 is for determining a flat portion of the image (hereinafter simply referred to as a flat portion), and the threshold value DELTA 2 is a peak portion of the image or a bottom portion of the valley of the image (hereinafter simply referred to as the top of the mountain or the valley). Threshold value LEVEL is for determining an edge.
[0036]
Hereinafter, the edge detection operation of the edge detection unit 2 will be described with a specific example of the pattern of the image.
[0037]
(1) As a first edge determination criterion for edge determination by the edge detection means 2, two flat portions having different signal levels are detected during the determination sample period, and these flat portions are not flat portions. The part is an edge.
[0038]
FIG. 5 shows a specific example of a determination sample period in which an edge can be determined based on the first edge determination criterion. FIG. 5B shows a sample period T input to the edge detection means 2. Digital image signal S ₁ It is. FIG. 5A shows the digital image signal S. ₁ For convenience, an example of a continuous waveform of the digital image signal S is shown. ₁ Is obtained by sampling the image signal shown in FIG.
[0039]
In FIG. 5B, here, the determination sample period is four times the sample period T, that is, 4T, and the samples to be determined are samples A to E. The signal levels of the samples A, B, C, D, and E are A, B, C, D, and E, but the same applies to other edge determinations described later.
[0040]
For such determination sample periods A to E, the edge detection means 2 first obtains the absolute value | A−B | of the difference between the signal levels of the first two samples A and B, and when this is smaller than the threshold DELTA 1 (FIG. 4, “Yes” in step 100), the sample A and B are regarded as a flat portion. Next, the absolute value | B−C | of the difference between the signal levels of the samples B and C is obtained, and when this is smaller than the threshold DELTA 1 (“Yes” in step 101 in FIG. 4), the flat portion becomes the period of 2T. When no edge is detected (step 301 in FIG. 4), the processing of this determination sample period is terminated, and the same determination process is started in the next determination sample period starting from sample B with a shift of the sample period T.
[0041]
However, in FIG. 5B, since the absolute value | B−C | is equal to or greater than the threshold value DELTA 1 (“No” in step 101 in FIG. 4), the sample B is regarded as a flat portion, and further the samples C and D The absolute value | C−D | of the difference between the signal levels is obtained, and when this is smaller than the threshold DELTA 1 (“Yes” in step 102 in FIG. 4), the sample C and D are also regarded as a flat portion. As a result, two flat portions exist between the samples B and C. When the absolute value | B−C | of the signal levels of B and C is larger than the threshold LEVEL (step in FIG. 4). 109, “Yes”), the sample B and C are regarded as an edge (step 201 in FIG. 4), the determination process of the determination sample periods A to E is ended, and the determination process of the next determination sample period starting with the sample B Move on.
[0042]
However, when the absolute value | C−D | is larger than the threshold DELTA 1 (“No” in Step 102 of FIG. 4) and smaller than the threshold DELTA 2 (“No” in Step 103 of FIG. 4), or The absolute value | C−D | is larger than the thresholds DELTA 1 and 2 (“No” in step 102 and “Yes” in step 103), but the signal level C is not greater than the signal levels B and D. If it is not smaller (“No” in step 106 in FIG. 4), then the absolute value | D−E | of the difference between the signal levels of the samples D and E is obtained, and if this is smaller than the threshold DELTA 1 (“Yes” in step 104 in FIG. 4), the sample D and E are regarded as a flat portion. Therefore, between sample A and B and between sample C and D is a flat part.
[0043]
Based on the determination result, it is determined whether or not the sample B, D can be regarded as an edge. That is, the signal level continues to increase or decrease in the order of samples B, C, and D (“Yes” in step 107 of FIG. 4: sequentially increases in FIG. 5B), and the absolute value | B When −D | is larger than the threshold LEVEL (“Yes” in step 110 in FIG. 4), the region between the samples B and D is regarded as an edge (step 202 in FIG. 4).
[0044]
As described above, the digital image signal S shown in FIG. ₁ , Between these flat portions, that is, between the samples B and C (when the absolute value | C−D | is smaller than the threshold DELTA 1) or between the samples B and D (the absolute value | C−D | is the threshold DELTA 1). And when the signal levels B, C, and D sequentially rise or fall).
[0045]
In the determination process of the determination sample period (sample B → sample A, sample C → sample B,...) Starting from the next sample B after the determination process of the determination sample periods A to E ends, FIG. By performing the processing of steps 100, 111, 112, 303, or steps 100, 111, 112, 113, 117, 303 of FIG. 4, between samples B and C in FIG. Edges between D are not detected. That is, the same edge is not detected more than once.
[0046]
Further, the above is the edge where the signal level increases, but since the edge determination is performed using the absolute value of the signal level difference between the two samples, the same applies to the edge where the signal level decreases. is there. Therefore, in FIG. 5, if there is a falling edge thereafter, the immediately preceding flat part and the flat part after this edge are detected, and this falling edge is detected in the same manner as described above.
[0047]
(2) As the second edge determination criterion of the edge determination of the edge detection means 2, a mutation point such as a flat portion of the signal level and a peak portion of the signal level variation or a bottom portion of the valley is detected during the determination sample period. The edge is between the flat portion and the mutation point (regardless of their front-rear relationship). In the following, the variation point will be specifically described as the top of a mountain or the bottom of a valley from the relationship with the drawings.
[0048]
FIG. 6 shows a specific example of a determination sample period in which an edge can be determined based on the second edge determination criterion. In this specific example, a flat portion and a peak of a mountain are detected. It is said. FIG. 6B shows a digital image signal S having a sample period T input to the edge detection means 2. ₁ It is. FIG. 6A shows the digital image signal S. ₁ For the sake of convenience, as shown in the figure, it shows a start portion of an image representing a stripe pattern in which shading repeats every period of 2T or less. ₁ Is obtained by sampling the image signal shown in FIG. Also in this specific example, the determination sample period is 4T, and the samples to be determined are samples A to E.
[0049]
In FIG. 6B, the determination between samples A and B, the determination between samples B and C, and the determination between samples C and D are the same as the specific example shown in FIG. 5, and steps 100 to 103 in FIG. By the determination process of (106), between samples A to D, the area between samples A and B is determined as a flat portion.
[0050]
Next, an absolute value | D−E | of the difference between the signal levels of the samples D and E is obtained, and it is determined whether or not this is smaller than a threshold value. Here, when the absolute value | D−E | is larger than the threshold DELTA 1 (“No” in step 104 of FIG. 4) and further larger than the threshold DELTA 2 (“Yes” in step 105 of FIG. 4). Since the portion between the samples D and E is not a flat portion, according to the first determination criterion, the sample B and D that are not sandwiched between the two flat portions cannot be determined as an edge, and the determination is suspended. It becomes.
[0051]
Therefore, in this specific example, the second determination criterion is applied. That is, sample D has a higher signal level than samples B, C, and E and forms the top of the mountain, or small and the bottom of the valley (“Yes” in step 108 in FIG. 4), and samples B and D When the absolute value | BD− | of the signal level difference is larger than the threshold LEVEL (“Yes” in step 110 in FIG. 4), the sample B and D are determined to be edges (step 202 in FIG. 4). In other cases (that is, “No” in Steps 105, 108, and 110), the sample B and D are not regarded as edges (Step 303).
[0052]
In FIG. 6B, among samples B, C, and D, when sample C is the top of a mountain or the bottom of a valley (steps 103, 106, and 109), the edge between samples B and C is an edge ( Step 201 in FIG.
[0053]
In this way, the digital image signal S is indicated by the fine stripe pattern of the image. ₁ When a digital signal composed of a series of rectangular waves having a high frequency is sampled, the leading edge of the first rectangular wave that cannot be detected by the first criterion is detected by the second criterion. can do.
[0054]
In the specific example shown in FIG. 6B as well, in the next determination sample period starting from sample B (in this case, sample B → sample A, sample C → sample B,...), FIG. Steps 100, 111, 112, 113, 114, 118, 115 to 119, 304 or 116, (120), 305 are processed, and it is determined as an edge once in the processing of the previous determination sample periods A to E. The samples B and D are not determined as edges. Therefore, the same edge is not detected more than twice.
[0055]
(3) As a third edge determination criterion for the edge determination of the edge detection means 2, when the top of the mountain and the bottom of the valley are detected during the determination sample period, the top of the peak and the bottom of the valley The interval is the edge.
[0056]
FIG. 7 shows a specific example of a determination sample period in which an edge can be determined based on the third edge determination criterion. In this specific example, the top of a mountain and the bottom of a valley are detected. It is supposed to be. FIG. 7B shows a digital image signal S of sample period T input to the edge detection means 2. ₁ It is. FIG. 7A shows the digital image signal S. ₁ For convenience, an intermediate portion of an example of the continuous waveform is shown, and as shown in the figure, an image showing a stripe pattern in which shading is repeated every period of 2T or less is shown, and the digital image signal S ₁ Is obtained by sampling the image signal shown in FIG. Also in this specific example, the determination sample period is 4T, and the samples to be determined are samples A to E.
[0057]
In FIG. 7B, for the determination sample periods A to E, the edge detection means 2 first obtains the absolute value | A−B | of the difference between the signal levels of the first two samples A and B, It is determined that it is larger than the threshold DELTA 1 (“No” in step 100 of FIG. 4) and larger than the threshold DELTA 2 (“Yes” in step 111 of FIG. 4). Next, the absolute value | B−C | of the difference between the signal levels of the samples B and C is obtained, and it is determined that this is larger than the threshold DELTA 1 (“No” in step 112 in FIG. 4). When the absolute value | B−C | is smaller than the threshold value DELTA 1 (“Yes” in step 112 in FIG. 4), the edge between the samples B and C becomes a flat portion, so that no edge is detected (step in FIG. 4). 303) The process proceeds to the determination process between the next determination sample machines.
[0058]
Next, the absolute value | C−D | of the difference between the signal levels of the samples C and D is obtained, and this is larger than the threshold DELTA 1 (“No” in step 113 in FIG. 4) and smaller than the threshold DELTA 2 (in FIG. 4). “No” in step 114) or larger than the threshold DELTA 2 (“Yes” in step 114 in FIG. 4), but the signal levels of samples A, B, C, and D are A> B <C <D ( In step 118 of FIG. 4, “No”), the absolute value | D−E | of the difference between the signal levels of the samples D and E is obtained, and it is determined whether or not this is larger than the threshold DELTA 1 (step 115 of FIG. 4). In this case, the absolute value | D−E | is larger than the threshold DELTA 1 (“No” in step 115 in FIG. 4), and is larger than the threshold DELTA 2 (“Yes” in step 116 in FIG. 4). Since the signal levels of A to E are A> B <C <D> E (“Yes” in step 120 of FIG. 4), it is determined that the sample B is the bottom of the valley and the sample D is the top of the mountain.
[0059]
Then, an absolute value | BD− of the signal level difference between the samples B and D is obtained between the bottom of the valley and the top of the mountain, and when this is larger than the threshold LEVEL (in step 11 of FIG. Yes "), the sample B, D is determined as an edge (step 204).
[0060]
In FIG. 7B, when the sample C is the top of the mountain instead of the sample D, the process proceeds from step 114 to step 118 in FIG. 4 to make a “Yes” determination, and the sample B is the bottom of the valley. When the sample C is determined to be a peak, and the absolute value | BC of the signal level difference between the samples B and C is larger than the threshold LEVEL (“Yes” in step 11d of FIG. 4). The edge between the sample B at the bottom of the valley and the sample C at the top of the mountain is determined as an edge (step 203).
[0061]
Further, in FIG. 7B, assuming that the interval between the samples C and D is a flat portion (“Yes” in step 113 in FIG. 4), the signal levels of the samples A, B, and C are A> B <C. Therefore, the sample B is determined to be the bottom of the valley, and the difference in signal level between the sample B and the top sample C of the flat portion is determined according to the second determination criterion. Is greater than the threshold level LEVEL (“Yes” in step 11d in FIG. 4), the sample B and C are determined to be an edge (step 203 in FIG. 4).
[0062]
Further, in FIG. 7B, assuming that the portion between samples D and E is a flat portion (“Yes” in step 115 in FIG. 4), the signal levels of samples B, C, and D are B <C <D. ("Yes" in step 119 in FIG. 4), the sample B is determined to be the bottom of the valley, and the difference in signal level between the sample B and the top sample D of the flat portion is determined according to the second determination criterion. Is larger than the threshold LEVEL (“Yes” in step 11 in FIG. 4), it is determined that the edge between the samples B and D is an edge (step 204 in FIG. 4).
[0063]
Furthermore, in the specific example shown in FIG. 7, the rising edge between samples B and C or between samples B and D is detected, but processing is performed using the absolute value of the difference in signal level. Therefore, the same applies to the detection of the falling edge.
[0064]
In cases other than those described above, the edge between samples B and C or between samples B and D is not determined as an edge (steps 304 and 305 in FIG. 4).
[0065]
Returning to FIG. 1, as described above, the edge detecting means 2 receives the input digital image signal S. ₁ Detect edges of
[0066]
The edge generation means 3 is a digital image signal S detected by the edge detection means 7. ₁ Edge signal S using an edge coefficient K supplied from an interpolation control means (not shown) _E Is generated. This will be described with reference to FIG.
[0067]
FIG. 8 shows an edge period detected by the edge detection means 2, and B to F indicated by ◯ are digital image signals S in this edge period. ₁ B ′ to F ′ indicated by □ and ■ are edge signals S in this edge period. _E This is a sample.
[0068]
The edge generation means 3 is an edge period detected by the edge detection means 7, for example, the digital image signal S ₁ The samples B ′, C ′, D ′, E ′, and F ′ are sequentially generated corresponding to the samples B, C, D, E, and F, but the first sample B ′ in the edge period is the first sample. , The signal level of the jth sample (where j = 1, 2, 3, 4, 5) _j Then,
V _j = B + β _j × (F−B) (1)
However, B and F: Signal levels of samples B and F
0 ≦ β _j ≦ 1
It is represented by
[0069]
In the case of FIG. 8, the edge generation means 3 is represented by β _j = 1/2
V _k = (B + D) / 2
To obtain a digital image signal S ₁ Among the samples in the edge period, the signal level V _k Edge signal S at the timing of the sample with the signal level closest to (sample D in FIG. 8) _E This signal level V _k Samples (sample D ′ in FIG. 8), and the signal levels of all the samples preceding this sample D ′ (in this case, the signal levels V of samples B ′ and C ′) ₁ , V ₂ ) In the above formula (1) _j = 0 and signal level B, and the signal levels of all samples following this sample (sample D ′ in FIG. 8) (signal levels V of samples E ′ and F ′ in FIG. 8) _Four , V _Five ) In the above formula (1) _j = 1 and signal level F.
[0070]
Accordingly, in this case, the signal level V from the sample B ′ in the above equation (1). _j Coefficient β _j Is
0, 0, 0, 1/2, 1, 1, 1
It becomes. Such coefficient β _j Is supplied as an edge coefficient K from an interpolation control means (not shown).
[0071]
The edge coefficient K is not limited to this, and for example,
0,0,0,1,1,1,1
Or
0, 0, 1/3, 2/3, 1, 1, 1
Or
0, 0, 1/5, 1/2, 4/5, 1, 1
For example, it can be arbitrarily set as required.
[0072]
Thus, the edge signal S generated by the edge generation means 3 _E Is supplied to the mixing means 4 and this edge signal S _E And the digital signal S from the contour correcting means 1 _Three And the digital image signal S _Three Is generated.
[0073]
FIG. 9 shows this state, and an input digital image signal S as shown in FIG. ₁ When contour correction processing is performed by the contour correction means 1, as shown in FIG. 9B, an undershoot 10 occurs at the start of a period corresponding to the edge period detected by the edge detection means 2, which corresponds to this edge period. The overshoot 11 occurs immediately after the period.
[0074]
FIG. 9C shows the edge signal S as described above in the edge period detected by the edge detection means 2 generated by the edge generation means 3. _E And the digital image signal S shown in FIG. ₂ And at a predetermined ratio. Then, in the selection means 5, the digital image signal S shown in FIG. ₂ In the edge period detected by the edge detection means 2, the digital image signal S from the mixing means 4 _Three FIG. 9D shows the output digital image signal from the selection means 5. In this digital image signal, the period corresponding to the edge period detected by the edge detection means 2 is a digital image signal S from the mixing means 4. _Three The digital image signal S _Three The undershoot 10 generated at the start of the edge period by the correction processing by the contour correcting unit 1 is the edge signal S. _E Is reduced or suppressed.
[0075]
In this way, the undershoot 10 generated by the correction process of the contour correcting unit 1 can be reduced or suppressed, and the occurrence of black edges occurring in the contour portion of the image can be suppressed. As the brightness level difference between the edges forming the contour portion increases, the black edge appears more prominently. However, the above-described processing of this embodiment can suppress the occurrence of the black edge, thereby improving the image quality. A good image can be obtained.
[0076]
Also, the digital image signal S _Three In the edge period, the output digital image signal S of the contour correcting means 1 ₂ Edge signal S _E Are mixed, so this digital image signal S ₂ In comparison with the image, the edge of the slope becomes steeper. Therefore, in the image by the digital image signal output from the selection means 5, the black edge at the contour portion becomes inconspicuous, and the contour portion becomes clearer and sharpness is further improved. It becomes an image.
[0077]
It should be noted that the overshoot 11 occurs at the edge due to the correction processing of the contour correcting means 1, and this appears immediately after the edge period, so that the edge signal S _E It will not be affected by the mixing of and will remain as it is. For this reason, the contour portion of the image is remarkably expressed, and a high-quality image with high sharpness can be obtained while suppressing the occurrence of black edges.
[0078]
In FIG. 9, the rising edge (contour portion) has been described as an example. However, in the falling contour portion, overshoot due to contour correction is added after the contour portion. For this reason, the edge detector 3 (FIG. 1) receives the input digital image signal S. ₁ The overshoot will be shifted later from the edge period detected from. Therefore, the edge detection unit 2 shifts the edge detection timing, thereby delaying the edge signal SE generated by the edge generation unit 3 and the operation of the selection unit 5 by the shift of the edge detection timing. For example, when the contour correcting unit 1 performs contour correction by the method described with reference to FIGS. 2 and 3, the undershoot added to the falling contour portion is the input digital image signal S. ₁ Is delayed by 2T, which is twice the sample period T. Therefore, when the edge detection unit 2 detects an edge (contour part), the edge detection unit 2 determines whether or not the contour part is rising by comparing the signal levels of the start sample and the end sample, and is a falling contour part. Sometimes, the edge signal S of the edge generation means 3 _E Is delayed by 2T, and the operation of the selection means 5 is similarly delayed.
[0079]
In the above embodiment, only undershoot due to contour correction at the contour portion is suppressed, but overshoot may also be suppressed. Thereby, it is possible to eliminate abnormal “glare” in the contour portion of the image. In order to perform such correction processing, the image signal S of the selection means 5 in FIG. _Three The period (that is, the edge period) for selecting the image may be extended so as to extend to the period in which the overshoot after the end of the edge period of the contour portion exists. For example, taking FIG. 9 as an example, the selection means 5 is connected to the image signal S. _Three The period for selecting is extended to a period in which overshoot occurs rather than the edge period shown in the figure. Of course, the edge signal S _E Also at least until this extension period. In addition, by doing this, even when the contour portion includes a falling edge, the same edge signal S is used. _E Can be used.
[0080]
As described above, even if undershoot is suppressed or even overshoot is suppressed, the mixing process in the mixing unit 4 causes the edge to be steeper than the result of the correction process in the contour correcting unit 1. The contour correction effect is improved.
[0081]
FIG. 10 is a block diagram showing an embodiment of an imaging apparatus and method according to the present invention using the image signal processing apparatus described above. 11 is a CCD (Charge Coupled Device) imaging element, 12 is CDS (Correlated Double Sampling) circuit, 13 AGC (Automatic Gain Control) circuit, 14 A / D (analog / digital) converter, 15 Y (luminance) / C (chroma) Separation circuit, 16 is a luminance signal processing circuit, 17 is a gamma correction circuit, 18 is a contour correction circuit, 19 is a synchronization adding circuit, 20 is a D / A (digital / analog) converter, 21 is a color signal processing circuit, 22 and 23 Is a D / A converter.
[0082]
In the figure, a CCD image sensor 11 captures an image (not shown) and outputs an electrical signal corresponding to the image. This electric signal is waveform-shaped by the CDS circuit 12 and a pixel signal is extracted. The gain is controlled by the AGC circuit 13 so that the amplitude is constant, and then supplied to the A / D converter 14 to generate a digital image signal. Is done. This digital signal is separated into a digital luminance signal Y and a digital color signal C by the Y / C separation circuit 15, the digital luminance signal Y is supplied to the luminance signal processing circuit 16, and the digital color signal is supplied to the color signal processing circuit 21. The
[0083]
In the luminance signal processing circuit 16, the input digital luminance signal Y is gamma-corrected by the gamma correction circuit 17, the contour portion is corrected by the contour correction circuit 18, and a synchronization signal is added by the synchronization adding circuit 19. The The digital luminance signal Y subjected to the above processing is output from the luminance signal processing circuit 16 and converted into an analog luminance signal by the D / A converter 20 to obtain a luminance signal Y of a predetermined method such as the NTSC method.
[0084]
On the other hand, the digital color signal C separated by the Y / C separation circuit 15 is subjected to processing such as separation into a current signal, white balance, and gamma correction by the color signal processing circuit 21, and then the digital color difference signal RY. , B-Y are generated and modulated for each. These digital color difference signals RY and BY are respectively supplied to D / A converters 22 and 23 and converted into analog signals to obtain color difference signals RY and BY of a predetermined system such as the NTSC system.
[0085]
In this embodiment, the image signal processing apparatus according to the present invention described above is used as the contour correction circuit 18 in the luminance signal processing circuit 16 in the imaging apparatus having such a configuration. As a result, the luminance signal Y obtained from the D / A converter 20 is contour-corrected, but the undershoot due to the contour correction processing is suppressed to become a luminance signal, and an image based on the image signal obtained by the imaging device is obtained. Then, the black edge becomes inconspicuous in the contour portion.
[0086]
Note that the embodiment shown in FIG. 10 shows an example of the present invention, and the present invention is not limited to this. Any imaging apparatus having a contour correction circuit may be used as the contour correction circuit described above. Needless to say, an image signal processing device shown as a form can be used, and thereby an imaging device according to the present invention can be formed.
[0087]
【The invention's effect】
As described above, according to the present invention, it is possible to suppress the occurrence of black edges in the contour portion of the image due to the contour correction, and further to suppress the glare in the contour portion. A high-quality image can be obtained while maintaining a good image sharpness.
[Brief description of the drawings]
FIG. 1 is a block diagram showing a configuration of an embodiment of an image signal processing apparatus and method according to the present invention.
2 is a block diagram showing a specific example of contour correction means in FIG. 1. FIG.
FIG. 3 is a waveform diagram showing signals at various parts in the specific example shown in FIG. 2;
4 is a flowchart showing a specific example of the operation of the edge detection means in FIG. 1. FIG.
FIG. 5 is a diagram showing a specific example of a digital image signal to be processed by the edge detection unit in FIG. 1;
6 is a diagram showing another specific example of the digital image signal to be processed by the edge detection unit in FIG. 1. FIG.
FIG. 7 is a diagram showing still another specific example of the digital image signal to be processed by the edge detection unit in FIG.
8 is a diagram showing a specific example of the operation of the edge generation means in FIG. 1. FIG.
9 is a diagram for explaining an image signal output from the selection unit in FIG. 1; FIG.
FIG. 10 is a block diagram showing an embodiment of an imaging apparatus and method according to the present invention.
[Explanation of symbols]
1 Contour correction means
2 Edge detection means
3 Edge generation means
4 Mixing means
5 selection means
6 Input terminal
7 Output terminal
8 Edge enhancement means
10 Undershoot
11 Overshoot
20 CCD image sensor
23 A / D converter
24 Y / C separation circuit
25 Luminance signal processing circuit
27 Contour correction circuit
29 D / A converter

Claims (10)

In an image signal processing apparatus having a plurality of contour correction means for performing contour correction processing on an input digital image signal and a selection means for selecting one of the plurality of contour correction means.
One predetermined contour correcting unit among the plurality of contour correcting units includes a contour detecting unit that detects a contour of the input digital image signal, and a contour correcting unit other than the predetermined contour correcting unit. Consists of contour correction means for correcting the contour of the digital image signal subjected to contour correction,
The image signal processing apparatus characterized in that the selection means selects a digital image signal output from the outline correction means when an outline is detected by the outline detection means. 2. The contour correction unit according to claim 1, wherein the contour correction unit other than the predetermined contour correction unit performs contour correction by causing undershoot and overshoot in a contour portion of the input digital image signal. Image signal processing device. In claim 2,
The contour correction means includes a contour correction signal generation means for generating a contour correction signal in accordance with a contour portion of the input digital image signal, the contour correction signal output from the contour correction signal generation means, and the predetermined correction signal. The digital image signal contour-corrected by the contour correction means other than the contour correction means is mixed at a predetermined ratio, and is composed of mixing means for suppressing undershoot of the contour-corrected digital image signal,
The image signal processing apparatus according to claim 1, wherein the selecting means selects an output digital signal of the mixing means when a contour portion is detected by the contour portion detecting means. In claim 3,
The contour detection means determines whether the detected contour is a rising contour or a falling contour, and when the detected contour is a falling contour, delays the detection timing of the contour period,
The image signal processing apparatus, wherein the contour correction signal generation unit generates the generated contour correction signal in accordance with the contour period detected by the contour detection unit. In any one of Claims 1-4,
The contour detection means is
A first means for considering a flat portion when the variation of the digital image signal is within a preset threshold range;
When the slope between the two flats detected by the first means always rises or falls and the absolute value of the signal level difference at the slope is greater than a preset threshold, An image signal processing apparatus comprising: a second unit that regards a gap as a contour portion of the digital image signal. In any one of Claims 1-4,
The contour detection means is
A first means that considers flat when the variation of the digital image signal is within a preset threshold range;
A second means for regarding the variation point at which the fluctuation of the digital image signal shifts from a slope that rises or falls sequentially to a slope that rises or falls as a peak of a mountain or a bottom of a valley;
When the absolute value of the difference in signal level between the flat portion detected by the first means and the mutation point detected by the second means is larger than a preset threshold, the flat portion and the An image signal processing apparatus comprising: a third unit that regards a portion between the variation points as an outline portion of the digital image signal. In any one of Claims 1-4,
The contour detection means is
The first variation point at which the fluctuation of the digital image signal shifts from the slope that rises or falls sequentially to the slope that descends or rises is regarded as the top of the mountain or the bottom of the valley, and it gradually falls or rises from the first mutation point. A first means for setting the second mutation point that rises or descends after the slope as the bottom of the valley or the top of the mountain;
When the absolute value of the signal level difference between the first and second mutation points detected by the first means is larger than a preset threshold value, the gap between the first and second mutation points is An image signal processing apparatus comprising: a third means that is regarded as a contour portion of a digital image signal. Imaging means for imaging a subject and outputting an electrical signal;
An imaging apparatus comprising: signal processing means for processing an electrical signal output from the imaging means to generate a first digital image signal; and image signal processing means for correcting the contour of the first digital image signal ,
An image pickup apparatus using the image signal processing apparatus according to claim 1 as the image signal processing means. A first digital image signal obtained by contour-enhancing the input digital image signal to generate a contour correction, and a second digital image signal for suppressing undershoot at the emphasized contour portion of the first image signal are generated. And
An image signal processing method comprising: selecting the second digital image signal in a contour period, and selecting and outputting the first digital signal in a period other than the contour period. An image pickup method for obtaining a digital image signal by performing signal processing on an image signal obtained from a photographing means, and correcting the contour of the digital image signal,
An image pickup method, wherein the contour correction processing of the digital image signal is performed using the image signal processing method according to claim 9.

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