JPH0326875B2 - - 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 required for this detail emphasis processing can be obtained optically or analogously by using an aperture having a larger diameter than the aperture for obtaining the sharp signal S. However, in this method, apart from the optical system for obtaining the sharp signal S, the unsharp signal U is
The aperture diameter for the sharp signal S needs to be adjusted according to the type of input image (line drawings and images with gradations), the duplication magnification, and the number of screen lines during halftone dot duplication. It is necessary to change the aperture diameter for the unsharp signal U in response to this change, which has disadvantages such as being time-consuming and complicating the mechanical system. 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 circuit (for creating an unsharp signal U) uses multipliers or adders whose number corresponds to the diameter (physical aperture 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 Problem" In the present invention, as a means for solving the above problem, for example, among the image signal string of an arbitrary number of pixels sequentially inputted by photoelectric scanning in the main scanning direction, the main scanning The sum of the first image signal sequence is obtained by adding the image signals of a required number of consecutive pixels in the direction or the sub-scanning direction, and the image signals of the same number of consecutive pixels subsequent to the required number of pixels are added. to find the sum of the second image signal sequence, and then calculate the sum of the first image signal sequence and the second image signal sequence.
Unsharp in the main scanning direction or sub-scanning direction (one dimension) by sequentially cumulatively adding and subtracting the sum of the image signal strings for the image signal strings (described in detail in the operation explanation section in Table 1). I'm getting a 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. The product is obtained by multiplying the image signal of one of the pixels by the same number as the number of pixels forming the image signal string, and the product of the sum of the image signal string and the image signal of the pixel at one end of the image signal string is calculated as the image signal. An unsharp signal in the main scanning direction or sub-scanning direction (one-dimensional) is obtained by sequentially performing cumulative addition and subtraction on the columns. 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 sum of the first unsharp signal sequence and the sum of the second unsharp signal sequence in the same manner as described above,
A two-dimensional (main scanning direction and sub scanning direction) unsharp signal is obtained. Note that the weighting coefficient W of the unsharp signal given to each image signal is a value l indicating the position of the pixel of that signal.
(See FIG. 13, a number that increases sequentially from both ends toward the center pixel) has the relationship W∞l ⁿ . ``Embodiment'' First, an image scanning recording apparatus to which the present invention is applied will be briefly described based on FIG. red (R), green
(G), blue (B) are converted into three analog color (electrical) signals. 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 signal is converted into each color version signal of yellow (Y), magenta (M), cyan (C), 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. For each color plate signal, a color selector (a device that controls multicolor simultaneous output processing or single color output processing) 45 selects the signal of the color plate to be duplicated, and a detail emphasis circuit 46 (to be described later) processes 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 cost 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, an image signal d input to the filtering circuit used in the present invention, a number l indicating the position of a 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, image signals (d _k to d - _k+2 ) of (2k-1) pixels in either the main scanning direction or the sub-scanning direction, or both, input from the color sorter.
Filtering processing is performed on the Therefore, a pixel position number l is 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 shift register V described below
And the position of each element in the line memory L is marked with a symbol k...
1, 0, -1...-k are attached. However, the element V _k or the line memory L _k corresponding to the symbol 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 receive the current addition signal P and the current subtraction signal Q, respectively, and the previous calculations of the addition/subtraction circuits stored in registers 5, 6, and 7, respectively. A cumulative addition/subtraction process of P-Q+R is performed from the result (cumulative addition/subtraction signal from the start of photoelectric scanning to one clock before the current time) R. (Hereinafter, such cumulative addition/subtraction processing will be expressed as cumulative addition/subtraction of signal P and signal Q, omitting the description of R as a general rule.) Note that 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 ( (sum of the first image signal sequence), and is input as an addition signal to the cumulative adder/subtractor 4 at the next stage. In this sense, the cumulative addition/subtraction circuit 2 is considered to be the first addition means. 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 (second (sum of the image signal sequence) and is input to the next stage cumulative adder/subtractor 4 as a subtraction signal. In this sense, the cumulative addition/subtraction circuit 3 is considered to be a second addition means. 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. A predetermined number k (positive integer) of pixels is set for a pixel row obtained by photoelectrically scanning an original image through an aperture for sharpening signals in accordance with an aperture size for unsharp signals, The signal of the first pixel column is obtained by adding each pixel signal of k consecutive pixels (V _k , V _k-1 , ..., V ₁ ) in the pixel column continuous in the main scanning direction or sub-scanning direction. The sum is calculated, and the same number of consecutive pixels (V ₀ , V _-1 ,...,
The signal sum of the second pixel column is obtained by adding the image signals of the pixels V _-k+1 ), and the current first signal sum is added to the previous cumulative addition/subtraction value to obtain the second signal. An image signal filtering method in which an unsharp signal is obtained by sequentially performing cumulative addition and subtraction by subtracting a sum for each pixel of the first and second pixel columns. 2 The first signal sum and the second signal sum are:
The image signal filtering method according to claim 1, wherein the difference between the image signals at both ends of each of the (k+1) consecutive pixels is determined for each of the k consecutive pixels, and then accumulated and added. . 3. The first signal sum obtained for each pixel in the first pixel column is sequentially stored in a storage means, and the second signal sum is delayed by the number of pixels k from the storage means. The image signal filtering method according to scope 1. 4. Storage means for storing each pixel signal of a pixel column in a scanning order obtained by scanning an original image, and k consecutive pixels (pixels set corresponding to the aperture size for unsharp signals a first addition means for adding each pixel signal of the pixels of (number) to obtain a signal sum of a first pixel column; and adding each pixel signal of k consecutive pixels following the first pixel column a second addition means for calculating the signal sum of the second pixel column by adding the current first signal sum and subtracting the current second signal from the previous calculation output value; An image signal filtering device comprising: cumulative addition/subtraction means for performing cumulative addition/subtraction, and obtaining an unsharp signal from the output of the cumulative addition/subtraction means. 5 The first addition means and the second addition means are
5. The image signal filtering device according to claim 4, wherein the image signal filtering device is an adding means that calculates and accumulates the difference between the image signals at both ends of each of the (k+1) consecutive pixels for each of the k consecutive pixels. 6. Storage means for sequentially and individually storing the first signal sum obtained for each pixel and outputting the first signal sum delayed by K pixels as the second signal sum is referred to as the second addition means. An image signal filtering device according to claim 4.