JPH09233342A - Contour emphasis method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To conduct proper contour emphasis depending on a characteristic by detecting a gradation characteristic of an object image and changing the level of the contour emphasis signal based on the detected gradation characteristic. SOLUTION: A film image is scanned and point sequential R, G, B digital images are received by an integration block 41 via a CCD line sensor 14 and an A/D converter 18 or the like. The integration block 41 generates gradation data in an integration area with respect to one image pattern and a frequency of each gradation is counted based on the generated gradation data, a simple histogram is generated and outputted to a CPU 40. The CPU 40 obtains a reference minimum value and a reference maximum value of the digital image signal and obtains a selection signal representing a kind of a selected contour emphasis processing and outputs them to a digital signal processing circuit 20, which conducts the contour emphasis processing of a kind represented by the selection signal.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a contour enhancement method, and more particularly to a contour enhancement method for adding a contour enhancement signal to an image signal to enhance the contour of a subject image.

[0002]

2. Description of the Related Art Conventionally, there has been known an image reproducing apparatus for photographing a film image photographed on each frame of a film by an image pickup device such as CCD and reproducing and displaying the picked-up image on a display device such as a TV monitor. In such an image reproducing apparatus, Japanese Patent Application Laid-Open No. 6-253147 proposes an image reproducing apparatus that applies contour correction processing and the like according to shooting conditions and corrects the image quality to a suitable one.

[0003]

The sharpness of an image is most affected by the gradation characteristics of the film image recorded on the film. For example, an image with a narrow gradation dynamic range and a low contrast (sleepy) is perceived as having insufficient sharpness as compared with an image that is not. On the contrary, an image with a wide dynamic range and a high contrast has a good sharpness.

Therefore, if the same edge enhancement processing is performed on both sides, the final image will have a completely different impression, and if the same amount of edge enhancement signals as an image with low contrast is added to an image with high contrast, Image quality deteriorates. Therefore, in order to automatically and properly perform the contour correction processing, it is necessary to judge the features of the image in some form. The present invention has been made in view of such circumstances, and an object of the present invention is to provide a contour enhancement method that automatically determines the features of an image and performs appropriate contour enhancement processing.

[0005]

In order to achieve the above-mentioned object, the present invention provides a contour enhancement method for adding a contour enhancement signal to an image signal obtained by imaging a subject,
The feature is that the gradation characteristic of the subject image is detected, and the magnitude of the contour emphasis signal is changed based on the detected gradation characteristic.

According to the present invention, for example, the reference maximum value and the reference minimum value of the image signal are detected from the image signal, and the difference or ratio between the reference maximum value and the reference minimum value is calculated. If this difference or ratio is less than or equal to the reference value for determining the richness of gradation, the contour enhancement signal is made stronger than usual and added. As a result, it is possible to perform appropriate contour enhancement processing according to the characteristics of the image without causing image quality deterioration.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of a contour emphasizing method according to the present invention will be described below in detail with reference to the accompanying drawings. FIG.
FIG. 1 is a block diagram of essential parts showing an embodiment of a film scanner to which the present invention is applied. This film scanner mainly includes a light source 10 for illumination, a photographing lens 12, and a CC.
D line sensor 14, analog amplifier 16, A / D converter 18, digital signal processing circuit 20, motor 31,
A film drive device including a capstan 32 and a pinch roller 33, a central processing unit (CPU) 40, and the like are provided.

The light source 10 illuminates the developed negative film 52 drawn out from the film cartridge 50 through an infrared cut filter (not shown), and the film 52 is illuminated.
The transmitted light transmitted through is imaged on the light receiving surface of the CCD line sensor 14 via the taking lens 12. The CCD line sensor 14 is placed in the direction 102 orthogonal to the film transport direction.
A light receiving portion for four pixels is provided, and the image light imaged on the light receiving surface of the CCD line sensor 14 is provided with R, G, and B filters, and charges are accumulated in each light receiving portion. It is converted into R, G, and B signal charges in an amount corresponding to the height. The R, G, and B charges accumulated in this way are transferred to the shift register when a read gate pulse of one line cycle applied from the CCD drive circuit 15 is applied, and then sequentially converted into voltage signals by register transfer pulses. Is output. Further, the CCD line sensor 14 is provided with a shutter gate and a shutter drain adjacent to each light receiving portion. By driving this shutter gate with a shutter gate pulse, the electric charge accumulated in the light receiving portion is shutter drained. Can be swept up to. That is, the CCD line sensor 14 has a so-called electronic shutter function capable of controlling the electric charge accumulated in the light receiving portion according to the shutter gate pulse applied from the CCD drive circuit 15.

The R, G, B voltage signals read from the CCD line sensor 14 are clamped by a CDS clamp (not shown) and added to the analog amplifier 16, and the gain is controlled as described later. The R, G, B voltage signals for one frame output from the analog amplifier 16 are dot-sequential R, G, B by the A / D converter 18.
After being converted into the B digital image signal, the digital signal processing circuit 20 performs white balance, black balance, negative / positive inversion, gamma correction, contour correction, etc., and the YCC conversion circuit 35 performs the luminance signal Y and the chroma signals C _r, C. converted to _b . Then, the luminance signal Y and the chroma signals C _{r and} C _b passed through the chroma suppression circuit 36 are stored in an image memory (not shown).

The luminance signal Y and the chroma signals C _r, C _{b for} one frame stored in the image memory are repeatedly read and converted into analog signals by the D / A converter, and then the NTSC system is used by the encoder. Is converted into a composite video signal and output to an image output device such as a monitor TV or a printer. As a result, the film image can be viewed on the monitor TV or the printer.

The film drive device engages with the spool 50A of the film cartridge 50, and the spool 50A
A film supply unit that drives the film in the normal / reverse direction, a film winding unit that winds the film 52 sent from the film supply unit, and a capstan that is disposed in the film transport path and that drives the film 52 by a motor 31. It is constituted by means for sandwiching it between 32 and the pinch roller 33 and conveying the film 52 at a desired speed. The film supply section is a spool 50A of the film cartridge 50.
1 is driven clockwise in FIG. 1 to feed the film 52 from the film cartridge 50 until the leading end of the film is wound by the film winding section.
Further, the CPU 40 controls the motor speed / direction control circuit 34.
Through this, the forward / reverse rotation of the motor 31, the start / stop, and the film transport speed by pulse width modulation can be controlled.

Now, when the film cartridge 50 is set in the cartridge storing portion (not shown), the film 52 is sent out from the film cartridge 50 and the leading end of the film is wound around the winding shaft of the film winding portion (the film loading is When completed), the film 52 is transported at a constant speed. As a result, the film image is scanned, and the dot-sequential R, G, B digital image signals are captured by the integrating block 41 via the CCD line sensor 14, the analog amplifier 16 and the A / D converter 18.

The integrating block 41 integrates the gradations (9-bit (0 to 511) gradations) of the digital image signals in a predetermined integration area for each R, G, B digital image signal, The average gradation of the integrated area is obtained, and each gradation data of the integrated area of 5000 to 10000 points is created per screen. Furthermore, the integration block 41 counts the frequency for each gradation based on the gradation data that is sequentially created, and this frequency is a threshold value TH (the total number of points in this embodiment) set for the total number of points of the gradation data. 1%) of the above, the counting is stopped. That is, the integration block 41 creates a simple histogram (histogram shown by diagonal lines in FIG. 2) that counts up to the maximum threshold value TH for all gradations from 0 to 511 as shown in FIG. To do. The number of bits of the counter can be greatly reduced by not counting the frequency that exceeds the threshold TH. The two-dot chain line in FIG. 2 is the original histogram when the total number of points is counted.

The CPU 40 sequentially accumulates frequencies from the smallest gradation of the simple histogram shown in FIG. 2, and the gradation when the accumulated frequency matches or first exceeds the threshold value TH is a reference minimum value. As the R, G, and B values, the frequencies are sequentially accumulated from the one with the highest gradation in the simple histogram, and the gradation when the accumulated frequency matches or first exceeds the threshold TH is the reference maximum value. As R, G, B. In the following description, the reference minimum value is D _min and the reference maximum value is D _max, and D _min and D _max are reference minimum values or reference maximum values of any of R, G, and B.

Then, the data of the reference minimum value D _min and the reference maximum value D _max of the digital image signal thus obtained are output to the digital signal processing circuit 20. The digital signal processing circuit 20 adjusts white balance and black balance based on these data. Further, the CPU 40 selects an appropriate contour enhancement process based on the data of the reference minimum value D _min and the reference maximum value D _max (“normal”, “strong”, “weak”).
The appropriate contour enhancement processing is selected from the three types of contour enhancement processing. The details will be described later. ), The digital signal processing circuit 20 outputs a selection signal indicating the selected type of contour enhancement processing.
Output to The digital signal processing circuit 20 performs the edge enhancement processing of the type indicated by this selection signal. Hereinafter, this outline emphasis processing will be described in detail.

As described above, the CPU 40 sets the reference minimum value D
"Normal" based on the data of _min and the reference maximum value D _max ,
An appropriate contour enhancement process is selected from among three types of contour enhancement processes of “strong” and “weak”. In the case of "strong" contour enhancement processing, a larger contour enhancement signal is added to the image signal than in "normal", and in the case of "weak" contour enhancement processing, a smaller contour enhancement signal is added to the image signal. To be added to.

Specifically, the difference between the reference maximum value D _max and the reference minimum value D _min (reference maximum value D _max -reference minimum value D min
_{When min} (hereinafter referred to as the dynamic range)) is larger than the reference value for judging the richness of gradation, that is, in the case of an image with high contrast, “normal” is selected. That is, when the dimic range is larger than the above reference value, the sharpness can be seen well, so the "normal" contour enhancement processing is performed.

On the other hand, when the dynamic range is less than the above reference value, that is, when the image has a low contrast,
Either “strong” or “weak” is selected according to the reference maximum value D _max . When the reference maximum value D _max is larger than the reference value for determining underexposure, “strong” is selected, and when the reference maximum value D _max is less than or equal to the reference value for determining underexposure,
Select "Weak".

That is, when the dynamic range is equal to or less than the reference value for judging the richness of gradation, since the image has a low contrast, a contour enhancement signal larger than "normal" is added. However, if the reference maximum value D _max is less than or equal to the reference value for determining underexposure, a portion with poor graininess is used for underexposure, and the grain noise of the film increases. Therefore, if an excessively large contour emphasis signal is added, the image quality is deteriorated, and on the contrary, the image is deteriorated. Therefore, a contour emphasis signal smaller than "normal" is added.

When the dynamic range is equal to or less than the reference value for judging the richness of gradation, the reference maximum value D _max is used to classify it into two _types , "strong" and "weak". You may set the range which selects "normal" between "weak". Further, the proper contour enhancement processing is determined by the difference between the reference maximum value D _max and the reference minimum value D _min , but the present invention is not limited to this, and it is determined by the function value of the reference maximum value D _max and the reference minimum value D _min. May be. For example, the ratio between the reference maximum value D _max and the reference minimum value D _min may be used.

As described above, the CPU 40 is "normal",
When any one of the three types of contour enhancement processing of “strong” and “weak” is selected, the selected “normal”,
A contour enhancement processing unit 6 that performs contour correction processing of the digital signal processing circuit 20 on a selection signal indicating either “strong” or “weak”.
2 (see FIG. 3). The contour correction processing unit 62 uses C
When a selection signal is input from the PU 40, contour enhancement processing is performed according to “normal”, “strong”, and “weak” indicated by the selection signal.

FIG. 3 is a block diagram showing an embodiment of the contour emphasis processing section 62. As shown in the figure, the contour emphasis processing unit 62 includes a calculation unit 64 and a memory 66. The calculation unit 64 reads out a look-up table corresponding to the contour enhancement processing indicated by the selection signal input from the CPU 40 from the memory 66, and calculates the contour enhancement processing by the filter processing and the coring processing.

A block diagram of the configuration of the arithmetic unit 64 is as follows:
As shown in the figure, the calculation unit 64 includes spatial filters 68A, 68B and 68C for R, G and B and a coring processing unit 70.
A, 70B, and 70C. Spatial filter 68
A, 68B, 68C have 5 × 5 filter coefficients,
As shown in FIG. 4A, the filter coefficients are arranged as shown in FIG. 4B with respect to the spatial arrangement of 5 × 5 image data. Then, the pixel values of A ₁₁ to A ₅₅ (where A ₃₃ is the target pixel a) of 5 × 5 pixels adjacent to the target pixel a shown in FIG. 4A and 5 shown in FIG. 4B. × 5 filter coefficient (Because it is vertically symmetrical, the filter coefficient is C
Convolutional integration with ₁ to C ₁₅ ) is performed, and the calculation result value (filter output) a ′ is calculated by the coring processing unit 7
Output to 0A, 70B, 70C.

Coring processing units 70A, 70B, 70C
Is a value (outline emphasis signal value) a ″ obtained by converting the filter output a ′ by the function f shown in FIG. 5 by inputting the pixel value of the target pixel a and the filter output a ′ of the spatial filter and the target pixel a. A value (output pixel value) A obtained by adding the pixel value and the pixel value is output. That is, assuming that a ″ = f (a ′), A = a + a ″ is output.

On the other hand, the spatial filters 68A, 68B, 68 for the "normal", "strong", and "weak" contour enhancement processing.
The filter coefficient of C and the coring processing units 70A and 70
The output values corresponding to the input values of B and 70C are recorded in the memory 66 as a lookup table. FIG. 6 is a diagram showing a data array pattern of the lookup table recorded in the memory 66.

As shown in the figure, the memory 66 stores R,
Data of the filter coefficients C ₁ to C ₁₅ of the spatial filters 68A, 68B, and 68C for G and B are recorded in order. Further, the coring processing units 70A, 7 for each of R, G, B
Regarding 0B and 70C, the output pixel value A corresponding to the pixel value of the target pixel a and the filter output a ′ of the spatial filters 68A, 68B, and 68C is recorded in order.

The computing unit 64 reads out a look-up table corresponding to the contour enhancement processing indicated by the selection signal input from the CPU 40 from the memory 66, sets the filter coefficients in the spatial filters 68A, 68B and 68C, and at the same time the coring processing unit 70A. , 70B and 70C, output value data corresponding to the input value is set, the above-described filter processing and coring processing are performed, and the image signal to which the edge enhancement signal is added is output.

The arithmetic unit 64 may be constructed as a circuit, or the arithmetic unit may be made to perform the above-mentioned arithmetic operation by software. In the above description, in the above embodiment, the reference minimum value and the reference maximum value of the density of the film image are obtained from the simple histogram, but the present invention is not limited to this, and the reference minimum value and the reference maximum value may be obtained by another method. Good.

Further, in the above embodiment, the contour emphasis processing is classified into three types, “normal”, “strong”, and “weak”, but the present invention is not limited to this, and more detailed steps may be provided. Further, the present invention is not limited to the film scanner of the above-described embodiment, and even in the case of image processing of a digital camera or the like, a dark subject with insufficient light amount has a lot of noise, and therefore the same processing as that of the above-described embodiment is required. It is also applicable to such a device.

[0030]

As described above, according to the contour emphasizing method of the present invention, the gradation characteristic of a subject image is detected, and the magnitude of the contour emphasizing signal is changed based on the detected gradation characteristic. Therefore, it is possible to perform the appropriate edge enhancement processing according to the characteristics of the image without causing the image quality deterioration. As a result, even a sleepy image with a small gradation difference can be corrected to an image with good sharpness without sacrificing other images. Further, even in the case of an image with a lot of noise, the noise can be corrected so as not to increase.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing an embodiment of a film scanner to which the present invention is applied.

FIG. 2 is a histogram used for explaining how to obtain a reference maximum value and a reference minimum value.

FIG. 3 is a configuration diagram showing an embodiment of a contour correction processing unit.

FIG. 4 is a diagram showing a filter coefficient of a spatial filter and an array of image data.

FIG. 5 is a diagram showing a function used for coring processing.

FIG. 6 is a diagram showing a data array pattern of a look-up table recorded in a memory 66.

[Explanation of symbols]

 10 ... Light source 12 ... Photographing lens 14 ... CCD line sensor 15 ... CCD drive circuit 18 ... A / D converter 20 ... Digital signal processing circuit 21, 22, 24 ... Adder 23, 26 ... Multiplier 25 ... Base LUT 31 ... Motor 40 ... Central processing unit (CPU) 41 ... Accumulation block 42 ... Address decoder 43R-45B ... Registers 46, 47, 48 ... Multiplexer 50 ... Film cartridge 52 ... Negative film 62 ... Edge enhancement processing unit 64 ... Arithmetic unit 66 ... Memory 68A , 68B, 68C ... Spatial filter 70A, 70B, 70C ... Coring processing unit

Claims (3)

[Claims] 1. A contour enhancement method in which a contour enhancement signal is added to an image signal obtained by picking up an image of a subject, the grayscale characteristic of a subject image is detected, and the contour enhancement is performed based on the detected grayscale characteristic. A contour enhancement method characterized in that the magnitude of a signal is changed. 2. A reference maximum value and a reference minimum value of the image signal are detected from the image signal, and a difference or a ratio between the reference maximum value and the reference minimum value is calculated. 2. The contour enhancement method according to claim 1, wherein the contour enhancement signal is made stronger than usual and added when the value is equal to or less than a reference value for judging abundance. 3. The contour according to claim 2, wherein when the reference maximum value is less than or equal to a reference value for determining underexposure, the contour emphasis signal is weaker than usual and added. Method of emphasis.