JPH0322116B2 - - Google Patents

Description

[Detailed description of the invention]

"Industrial Application Field" The present invention relates to an image signal filtering method and apparatus, and more particularly to an image signal filtering method and apparatus for obtaining an unsharp signal used in detail enhancement processing. "Conventional Example" Detail enhancement processing in image scanning and recording processing is performed by calculating S+K(S-U)( K:
This is achieved by performing the calculation (coefficient). The unsharp signal U necessary for this detail emphasis processing can be obtained in an optical analog manner by using an aperture having a larger diameter than the aperture for obtaining the sharp signal S. However, this method requires an optical system to obtain the unsharp signal U in addition to the optical system to obtain the sharp signal S, and the type of input image (line drawing and image with gradation). , it is necessary to change the aperture diameter for the sharp signal S according to the duplication magnification and the number of screen lines during halftone dot duplication, and it is necessary to mechanically change the aperture diameter for the unsharp signal U in accordance with this. There are disadvantages such as it is time consuming and the mechanical system is complicated. In order to eliminate the drawbacks of the above-mentioned analog system, the applicant of the present application disclosed a detail emphasis processing method using digital processing in Japanese Patent Application No. 54-82571, and also disclosed the This patent discloses a method that further improves the drawbacks of the technique disclosed in Japanese Patent Application No. 54-82571. In other words, a circuit that multiplies the image signals of an arbitrary number of pixels arranged in the scanning order by weighting coefficients W ₁ to _{W 15} and then adds and averages the signals, or a circuit that combines a doubler and an adder. This method uses However, this image signal filtering method (for creating an unsharp signal U) uses a number of multipliers or adders that correspond to the diameter (physical mask size) of the unsharp signal U. There is a drawback that the larger the diameter, the larger the number of multipliers or adders, and another drawback is that changing the weighting coefficient requires a separate circuit for changing each coefficient. "Means for Solving the Problems" In the present invention, as a means for solving the above problems, for example, among image signals of an arbitrary number of pixels sequentially inputted by photoelectric scanning in the main scanning direction, Alternatively, the sum of the first image signal sequence is obtained by adding the image signals of a required number of consecutive pixels in the sub-scanning direction, and then the image signals of the same number of consecutive pixels following the required number of pixels are added. By calculating the sum of the second image signal sequence and cumulatively adding and subtracting the sum of the first image signal sequence and the sum of the second image signal sequence, the sum of the second image signal sequence is calculated. ) is getting an unsharp signal. Further, for example, the sum of the image signal strings of a required number of continuous pixels in the main scanning direction or the sub-scanning direction obtained by photoelectric scanning in the main scanning direction, and whether the front end or the rear end of the required number of consecutive pixels is determined. multiplying the image signal of one of the pixels by the same number as the number of pixels forming the image signal string to obtain a product, and cumulatively adding and subtracting the sum of the image signal string and the product of the image signal of the pixel at one end thereof; An unsharp signal in the main scanning direction or the sub-scanning direction (one-dimensional) is obtained. Furthermore, after obtaining the unsharp signal in one direction (one dimension) of the main scanning direction or the sub-scanning direction, a required number of the one-dimensional signals that are continuous in the other direction of the main scanning direction or the sub-scanning direction are obtained. unsharp signals are added to obtain a first unsharp signal string, and the same number of consecutive one-dimensional unsharp signals following the required number of one-dimensional unsharp signals are added to obtain a second unsharp signal string By calculating the sum of the first unsharp signal sequence and the sum of the second unsharp signal sequence in a second cumulative addition and subtraction, two-dimensional (main scanning direction and sub-scanning direction) I am getting an unsharp signal. Note that the weighting coefficient W of the unsharp signal given to each image signal is W∝ ⁿ with respect to the value ( ) (a number that increases sequentially from both ends toward the center pixel, see Figure 13) indicating the position of the pixel of that signal. They have the following relationship. ``Embodiment'' First, an image scanning recording apparatus to which the present invention is applied will be briefly described based on FIG. 12. An original image A wound around an original image drum 41 is photoelectrically scanned by a scanning head 42. It is converted into analog color (electrical) signals of three colors: red (R), green (G), and blue (B). These signals are converted into digital color signals by the A/D converter 43 (or remain as analog signals without passing through the A/D converter 43), and are then converted to digital color signals by a known color calculator 44 (digital or analog). ), color correction and gradation correction are performed, and the signals are converted into color signals of yellow (Y), magenta (M), cyan (O), and black (K). Note that if the signal is still an analog signal, it is then converted to a digital signal through an A/D converter 43. A color selector (a device that controls simultaneous multi-color output processing or single-color output processing) 45 for each color plate signal selects the signal of the color plate to be duplicated, and a detail emphasis circuit 46 (described later) processes the sharpness (detail) emphasis. The photosensitive material B is then wound around the exposure drum 49 from the exposure head 48 via the halftone dot generator 47.
to expose. Each of the digital circuits described above is created by timing pulses input to a synchronous controller 52 from rotary encoders 50 and 51 provided on the original image drum 41 and the exposure drum 49, respectively.
It is synchronously controlled by clock pulses etc. output from. The detail emphasis circuit 46 includes the following image signal filtering circuit.
Detail emphasis processing is performed using the unsharp signal U and the sharp signal S. Next, the image signal d input to the filtering circuit used in the present invention, and the number indicating the position of the pixel of the image signal actually subjected to filtering processing,
Furthermore, the symbols assigned to each element V (or line memory L) of the shift register used in the filtering circuit are defined in FIG. In this invention, the image signal (d _k ~
d _-k+2 ) is subjected to filtering processing.
Therefore, pixel position numbers are assigned to the image signals of the (2k-1) pixels. However, since image signals of (2k+1) pixels are required in this processing process, the positions of each element of the shift register V and line memory L described below are coded k...1, 0, -1...- K is attached. However, the element V _k or line memory corresponding to code k
L _k may be omitted. FIG. 1 shows an embodiment of an image signal filtering circuit in which the present invention is applied to a one-dimensional (main scanning direction) image signal. First, the cumulative addition/subtraction circuits 2, 3, and 4 used here provide an addition signal P and a subtraction signal Q, as well as the previous calculation results of these addition/subtraction circuits stored in registers 5, 6, and 7 (at the start of photoelectric scanning). The cumulative addition/subtraction processing of P-Q+R is performed from the cumulative addition/subtraction signal R up to one clock before the current time. (From now on, such cumulative addition/subtraction processing will be
In principle, the description of R is omitted and the expression is expressed as cumulative addition and subtraction of signal P and signal Q. ) In addition, shift register 1 such as registers 5, 6, and 7
etc. and line memories 11, 15, 16, which will be described later.
17, etc., all have a clear function for initialization, and are always initialized before performing filtering processing. And (2k+1) stage elements V _k , V _k-1 ...V ₁ , V ₀
For example, an image signal D _i in the main scanning direction is sequentially input to the shift register 1 having V _-k , and the image signal d _k loaded into the first stage element V _k of the shift register 1 is transferred to the cumulative addition/subtraction circuit 2. The image signal d ₀ (delayed by k steps from d _k ), which is input as an addition signal to the shift register 1 and further loaded into the element V ₀ of the shift register 1, is input to the cumulative addition/subtraction circuit 2 as a subtraction signal. , is input as an addition signal to another cumulative addition/subtraction circuit 3. Further, the image signal d _-k (delayed by 2k stages from d _k ) loaded into the final stage element V _-k of the shift register 1 is input to the cumulative adder/subtractor 3 as a subtraction signal. The output signal U _1a of the cumulative adder/subtractor 2 is
As shown in Table (1), the sum (first The sum of the image signal sequences) is inputted to the next-stage cumulative adder/subtractor 4 as an addition signal. On the other hand, the output signal U _1b of the cumulative adder/subtractor 3 is as shown in Table 3.
As shown in equation (2), the sum of the image signals of the same number of consecutive pixels (corresponding to the radius of the mask size of the unsharp signal) following the required number of continuous pixels (second image (sum of the signal strings), and is input to the next stage cumulative adder/subtractor 4 as a subtraction signal. The relationship between the output signals of the cumulative adders/subtractors 2, 3, and 4 of the circuit configured as described above and the signals loaded into the shift register 1 is shown in detail in Table 1.

【table】

Claims (1)

[Claims] 1. Image signals of a required number of pixels consecutive in either the main scanning or sub-scanning direction obtained by photoelectrically scanning an original image are added to form a sum of a first image signal sequence. , and add the image signals of the same number of consecutive pixels following the required number of pixels to obtain the sum of the second image signal sequence, and calculate the sum of the first image signal sequence and the second image A one-dimensional unsharp signal for each pixel is obtained by sequentially performing the first cumulative addition and subtraction on the sum of the signal strings, and then the required number of unsharp signals consecutively in the other direction of main scanning or sub-scanning are obtained. One-dimensional unsharp signals are added to obtain a first unsharp signal sequence, and the same number of successive one-dimensional unsharp signals following the required number of one-dimensional unsharp signals are added to obtain a second unsharp signal sequence. An image signal in which a two-dimensional unsharp signal is obtained by calculating the sum of signal sequences and sequentially performing second cumulative addition and subtraction on the sum of the first unsharp signal sequence and the sum of the second unsharp signal sequence. Filtering method. 2. The sum of the first and second image signal sequences is calculated by sequentially cumulatively adding and subtracting the image signals of two pixels having a required interval among the pixel signals of pixels continuous in the main scanning direction or sub-scanning direction. The image signal filtering method according to claim 1, which requires at least one of the following. 3. A patent for obtaining at least one of the sums of first and second image signal sequences by sequentially adding image signals of a required number of consecutive pixels in the main scanning direction or sub-scanning direction using a plurality of adders. Claim 1
Image signal filtering method described in Section 2. 4. Claim 1 describes that the sum of the second image signal sequence is obtained by delaying the sum of the first image signal sequence by a required number of pixels in the main scanning direction or the sub-scanning direction in the storage means. image signal filtering method. 5. The first and second
2. The image signal filtering method according to claim 1, wherein at least one of the sums of unsharp signal sequences is obtained. 6. At least one of the sums of the first and second unsharp signal sequences is added by sequentially adding one-dimensional unsharp signals of a required number of consecutive pixels in the main scanning direction or the sub-scanning direction using a plurality of adders. An image signal filtering method according to claim 1, which requires the following. 7 The sum of the second unsharp signal sequence is obtained by delaying the sum of the first unsharp signal sequence by the required number of pixels in the main scanning direction or the sub-scanning direction in the storage means, as described in claim 1. image signal filtering method. 8 A line memory that stores image signals for one scanning line of (2k+1) lines (k is a positive integer) obtained by photoelectrically scanning the original image, and image signals of the first and (k+1)th line memories. a first cumulative adder/subtractor that cumulatively adds and subtracts the image signals of the (k+1)th and (2k+1)th line memories; A third cumulative adder/subtractor that further cumulatively adds and subtracts the addition output, a shift register that sequentially stores (2k+1) output signals of the third cumulative adder/subtracter, and a first and (k+1)th shift register. a fourth cumulative adder/subtractor that cumulatively adds/subtracts the signals of the (k+1)th and (2k+1)th shift registers; a fifth cumulative adder/subtractor that cumulatively adds/subtracts the signals of the (k+1)th and (2k+1)th shift registers; An image signal filtering device that obtains a two-dimensional unsharp signal, comprising a sixth cumulative adder/subtracter that further cumulatively adds and subtracts the output of the adder/subtracter, and a clock signal generator for synchronizing operations.