A method of modulating a multi-channel threshold matrix in multi-channel printing

Abstract

The application discloses a method for modulating a multi-channel threshold matrix in multi-channel printing and relates to the technical field of digital printing. Based on an original threshold matrix, different threshold matrices are modulated for each printing channel, so that different halftone images are output by different printing channels; the original threshold matrix is an image, and the value range of each pixel is a subset of the value range of a color component of an input continuous-tone image; the different threshold matrices generated for different channels are used for halftone processing of the input continuous-tone image, so that the printing effect is uniform, and the effect of saving printing ink is achieved.

Description

Technical Field

[0001] The present invention relates to the field of digital printing technology, and in particular to a modulation method of a threshold matrix in multi-channel digital printing technology. Background Art

[0002] In printing and reproduction, multi-channel printing technology is often used in order to pursue better color expression (for example, to make pure black text darker) or for certain special purposes (such as reducing the white line phenomenon caused by blockage of individual nozzles in inkjet printing technology).

[0003] Multi-channel printing technology refers to the use of the same color ink or ink in different color channels, so that the same color ink has multiple inking processes in the same printing area, thereby achieving the effect of enhancing color expression or reducing white line pulling.

[0004] Multiple channels using the same color ink or ink are often considered symmetrical, meaning that the continuous tone images input to these channels before halftoning are identical.

[0005] The bit depth of a continuous tone image is generally no less than 8 bits. Taking an image with an 8-bit bit depth as an example, each color component of each pixel can have a value from 0 to 255, a total of 256 cases. However, the bit depth supported by most printing devices is much smaller than that of a continuous tone image. Most printing devices only support a bit depth of 1 bit, that is, there are only two states: inked and uninked. Since the bit depth of a printing device is much smaller than that of a continuous tone image, the images that a printing device can accept are called halftone images. The most common method to convert a continuous tone image into a halftone image is to use a threshold matrix. The threshold matrix is ​​a grayscale image in which the value range of each pixel is a subset of the value range of the color component of the input continuous tone image.

[0006] In existing multi-channel printing technology, the same threshold matrix is ​​used for different channels of the same ink color or ink. The contone images before halftoning across multiple channels are identical. In existing technology, the threshold matrix for multiple channels is also identical, so the halftone images generated by the different channels are also identical.

[0007] However, outputting the same halftone image across different channels results in overly concentrated ink points. This, on the one hand, leads to uneven printing results, and on the other hand, affects the ink or prevents the color components in the ink from fully functioning, resulting in wasted ink. Existing technologies do not modulate different threshold matrices for different printing channels, making it difficult to achieve good printing results. Summary of the Invention

[0008] In order to overcome the above-mentioned deficiencies of the prior art, the present application provides a method for modulating multi-channel threshold matrix in multi-channel printing. By using the method, different threshold matrices can be modulated for each printing channel based on the initial or existing threshold matrix, so that different halftone images are output by different printing channels, thereby obtaining more uniform printing effect, and saving printing ink.

[0009] The different threshold matrices modulated for different printing channels have the following three characteristics:

[0010] First, the intersection of the set of pixel points with the same value in the threshold matrices of any two different printing channels is an empty set.

[0011] Second, let the number of printing channels be K, and the pixel value range of the input continuous tone image be 0-D; for a coordinate point in the threshold matrix of a printing channel, the pixel value of the coordinate point in the threshold matrix is a; if a×K is less than or equal to D, then for any two different printing channels (0<=i, j<K and i≠j), the intersection of the set of all coordinate points with pixel values less than or equal to a in the threshold matrices used by the two different printing channels (denoted as Φ i (a) and Φ j (a)) is an empty set.

[0012] Third, the threshold matrices of the multiple printing channels still maintain the properties of the original threshold matrix. Assuming that the original threshold matrix is T, the threshold matrices generated by T for K channels are T0...T K-1 , Num(T0,d)+...+Num(T k-1 ,d)≈(K×d) / D; the distribution of the union set of all pixels with pixel values less than or equal to d in the threshold matrices T0...T K-1 maintains the characteristics of the original threshold matrix T. Wherein, Num(T0,d) represents the number of pixels with pixel values less than or equal to d in the threshold matrix T0, and 0<=d<=D; Num(T,d)≈d / D.

[0013] To achieve the above-mentioned purposes, an embodiment of the present application provides a method for modulating multi-channel threshold matrix in multi-channel printing, which modulates different threshold matrices for each printing channel based on the existing threshold matrix. The method comprises the following steps:

[0014] 1) copying K same threshold matrices from the original threshold matrix: Th0..., Th k ,..., Th K-1 ;

[0015] 2) adding the value of all pixel points of the threshold matrix Th k by D×k, wherein 0<=k<K;

[0016] 3) Calculate the pixel point coordinate set sequence Ω Th (1),...,Ω Th (kd),...,Ω Th (K×D), wherein Ω Th (kd) represents the set of pixel point coordinates whose values are kd in all threshold value matrices Th0..., Th k ..., Th K-1 , wherein 1<kd<=K×D;

[0017] 4) Assign all elements in the set Ω Th (kd) to the threshold value matrices T0...T K-1 , and assign the value of the pixel point of the corresponding coordinate as , wherein represents the upward rounding. Any pixel point of any threshold value matrix T k can only be assigned once.

[0018] In the specific implementation, in order to enhance the effect of the present application, the present application further proposes a method for completing the above step 4), which can make the number of ink points generated by each channel as consistent as possible for any same input image. The method comprises the following steps:

[0019] a) initialize the processing variables, including the pixel value currently processed in the original threshold value matrix;

[0020] b) according to the order of the printing channel from 0 to K-1 and the pixel value from 1 to D, generate each channel threshold value matrix in turn according to the original threshold value matrix;

[0021] c) all pixel values in the threshold value matrix are processed according to b), to generate the threshold value matrix of each channel, and the processing is ended.

[0022] Compared with the prior art, the present application has the following beneficial effects:

[0023] Compared with the prior art of using the same threshold value matrix for different channels, the method can make the ink point distribution more reasonable in the multi-channel printing process, thereby significantly improving the uniformity of the printed matter, and fully playing the role of color components to achieve the effect of saving ink. DETAILED DESCRIPTION

[0024] The present application will be further described by examples below, but the scope of the present application is not limited in any way.

[0025] The present application provides a method for modulating multi-channel threshold matrix in digital printing. By using the method, different threshold matrix is modulated for each printing channel based on the original or existing threshold matrix, so that different halftone images are output by different printing channels, thereby obtaining uniform printing effect while saving printing ink.

[0026] In digital printing technology, the threshold matrix used is a gray scale image, in which the value of each pixel is a subset of the value range of the color component of the input continuous tone image. Assuming that the size of the input continuous tone image is X x Y, I(x, y) represents the value of the pixel at the xth row and yth column, where 0<=xX, 0<=yY. T(m, n) represents the value of the pixel at the mth row and nth column of the threshold matrix, where 0<=mM, 0<=nN; M and N are the width and height of the threshold matrix, respectively. Then the 1-bit depth halftone image H(x, y) processed using the threshold matrix is:

[0027] If I(x, y) >= T(x mod M, y mod N), then H(x, y) = 1; (In the >= judgment, the pixel value in the threshold matrix is generally not 0); otherwise H(x, y) = 0.

[0028] The threshold matrix usually has the following two properties:

[0029] Assuming that the value range of each pixel of the continuous tone image is 0-D, and Num(T, d) represents the number of pixels in the threshold matrix T whose value is less than or equal to d, where 0<=d<=D, then Num(T, d) ≈ d / D;

[0030] The distribution of the pixels in the threshold matrix T whose value is less than or equal to d in the M x N image satisfies certain characteristics, such as blue noise characteristics, or is closely connected with the center point of the threshold matrix as the core.

[0031] The present application provides a method for modulating multi-channel threshold matrix in multi-channel printing, which modulates different threshold matrix for each printing channel based on the existing threshold matrix, comprising the following steps:

[0032] 1) Copy K same threshold matrices Th0, Th1,..., ThK from the original threshold matrix Th0: k Th0, Th1,..., ThK K-1 ;

[0033] 2) Add D x k to the value of all pixel points of the threshold matrix Thk, where 0<=kK: k Th0, Th1,..., ThK

[0034] 3) Calculate the pixel point coordinate set sequence Ω(1),..., Ω(kd),..., Ω(Kd) of the threshold matrix Thk: Th Th0, Th1,..., ThK Th (kd),..., Ω(Kd)Th (k x D), where Ω Th (kd) represents the set of coordinates of all pixel points whose values are kd in the threshold matrix T0...T k ,...,Th K-1 where 1 < kd <= K x D.

[0035] 4) Assign all elements in the set Ω Th (kd) to the threshold matrix T0...T K-1 (each element is assigned and only once), and assign the value of the pixel point of the corresponding coordinate as where represents the upward rounding. Any pixel point of any threshold matrix T k can only be assigned once.

[0036] In order to enhance the effect of the present application, the present application also proposes a method for completing the above step 4), which can make the number of ink points generated by each channel as consistent as possible for any same input image. It includes the following steps:

[0037] 5) Initialize the processing variable;

[0038] 6) Generate each channel threshold matrix in order from channel 0 to K-1 and pixel value from 1 to D;

[0039] 7) Processing end judgment.

[0040] The above steps realize the modulation of different threshold matrices for each printing channel based on the existing threshold matrix, and the different threshold matrices obtained by modulation have the following three characteristics:

[0041] First, the intersection of the set of pixel points taking the same value in the threshold matrices of any two different printing channels is an empty set.

[0042] Second, let the number of printing channels be K, and the pixel value range of the input continuous tone image be 0-D; for the coordinate point in the threshold matrix of the printing channel, the pixel value of the coordinate point in the threshold matrix is a; if a x K is less than or equal to D, then for any two different printing channels (0 <= i, j < K and i ≠ j), the intersection of the set of all coordinate points whose pixel values are less than or equal to a in the threshold matrices used by the two different printing channels (denoted as Φ i (a) and Φ j (a)) is an empty set.

[0043] Third, the threshold matrices of multiple printing channels still maintain the properties of the original threshold matrix. Assuming that the original threshold matrix is T, the threshold matrices generated by T for K channels are T 0.. .T K-1Num(T0, d) +... + Num(T k-1 , d) ≈ (K x d) / D; threshold matrix T0...T K-1 The distribution of the union of all pixels with pixel value less than or equal to d in the M x N image keeps the characteristics of the original threshold matrix T.

[0044] The different threshold matrices generated for different channels are used for halftone processing of the input continuous tone image, so that the printing effect is uniform, and the printing ink is saved.

[0045] In the following embodiments, the number of printing channels is K, and the value range of the color component of the input continuous tone image for printing channels is 0-D. D is the upper limit of the value of the color component of the continuous tone image. The value of the pixel point in the original threshold matrix T is 1-D, and the threshold matrix generated for each printing channel is T0...T K-1 .

[0046] The threshold matrix is an image with a size of M x N, and the value range of each pixel is a subset of the value range of the color component of the input continuous tone image.

[0047] The original threshold matrix in the embodiment is as follows:

[0048] 1 32 8 40 2 34 10 42 48 16 56 24 50 18 58 26 12 14 4 36 14 46 6 38 60 28 52 20 62 30 54 22 3 35 11 43 1 33 9 41 51 19 59 27 49 17 57 25 15 47 7 39 13 45 5 37 63 31 55 23 61 29 53 21

[0049] The width (M) and height (N) of the above original threshold matrix are both 8; the bit depth of the continuous tone image processed by using the threshold matrix is 6 bits, that is, D is 63, and the value range of the pixel value is 0-63.

[0050] The method for modulating the multi-channel threshold matrix provided by the application comprises the following steps:

[0051] Step S1: copying K same threshold matrices Th0...Th K-1 from the original threshold matrix of the printing channel.

[0052] Step S2: adding D x k to the value of all pixel points of the threshold matrix Th k , where 0<=k<K;

[0053] Step S3: calculating Ω Th (1)...Ω Th (K x D), wherein Ω Th (kd) represents the set of pixel point coordinates with the value kd of all pixel points in the threshold matrix Th0...Th K-1 , where 1<kd<=K x D;

[0054] Step S4: distributing all elements in the set Ω Th (kd) to T0...TK-1 (each element is allocated only once), and the value of the pixel point at the corresponding coordinate is assigned as in Indicates rounding up. Any T k Any pixel can only be assigned once.

[0055] There are many ways to implement step S4. For example, the following assignment method can be used: However, the disadvantage of this method is that for any identical input image, the number of ink dots generated by each channel decreases as the channel index increases. This places an excessive burden on channels with smaller indexes (especially channel 0), causing the corresponding imaging units to deteriorate too quickly.

[0056] In order to enhance the effect of the present invention, the present invention proposes a method for completing step S4, which can ensure that the number of ink dots generated by each channel is as consistent as possible for any identical input image.

[0057] Assume that the number of different pixel values ​​appearing in the original threshold matrix T is D'. The least common multiple of K and D' is Z.

[0058] Taking the above original threshold matrix as an example, since the number of pixel values ​​that do not appear in the threshold matrix is ​​only 44, D'=62. When the number of printing channels K is 2, Z is equal to 62.

[0059] The method for completing step S4 provided by the present invention includes:

[0060] Step S41: Initialize processing variables,

[0061] kd=1; (kd represents the pixel value currently processed in the original threshold matrix)

[0062] k=0; (k represents the subscript of the multi-channel threshold matrix currently to be processed)

[0063] j = 0; (a control variable to prevent a pixel point in the multi-channel threshold matrix from being repeatedly assigned a value)

[0064] Step S42: Generate each channel threshold matrix in sequence from channel 0 to K-1 and pixel values ​​from 1 to D;

[0065] If Ω Th (kd) is not an empty set, then:

[0066] T (k mod K) Medium Ω T All corresponding pixels in the (kd) set are assigned

[0067] k = k + 1;

[0068] j = j + 1;

[0069] If (j mod Z) equals 0, k = k + 1.

[0070] Step S43: If all pixel values in the threshold matrix are processed, the process ends. At this time, all pixels of all threshold matrices of K channels are assigned and assigned only once.

[0071] kd = kd + 1;

[0072] If kd = K x D + 1, i.e. the threshold matrix T0...T K-1 has been generated, the process ends.

[0073] Repeat step S42.

[0074] The different threshold matrices generated for different channels are used for halftone processing of input continuous tone images, i.e. the effect of uniform printing and saving printing ink can be achieved.

[0075] In the case of two printing channels, the threshold matrices of two channels obtained by processing the original threshold matrix using the method of the present application (steps S1-S7) are as follows:

[0076] 1 48 36 52 33 49 37 53 24 40 28 44 25 41 29 45 38 39 34 50 39 23 35 51 30 46 26 42 31 47 27 43 2 18 6 22 1 17 5 21 57 10 61 14 56 9 60 13 8 55 4 20 7 54 3 19 63 16 59 12 62 15 58 11

[0077] and

[0078] 32 16 4 20 1 17 5 21 56 8 60 12 57 9 61 13 6 7 2 18 7 55 3 19 62 14 58 10 63 15 59 11 33 49 37 53 32 48 36 52 26 41 30 45 25 40 29 44 39 24 35 51 38 23 34 50 32 47 28 43 31 46 27 42

[0079] It can be seen that the sets of pixel points taking the same value in the two threshold matrices are completely non-overlapping. Among them, the former is the threshold matrix for channel 0; the latter is the threshold matrix for channel 1.

[0080] The halftone images obtained by processing a given image using the above two threshold matrices of two channels are as follows:

[0081] 1 0 0 0 0 0 0 0 1 0 1 0 1 0 1 0 0 0 0 0 0 1 0 0 1 0 1 0 1 0 1 0 1 1 1 1 1 1 1 1 0 1 0 1 0 1 0 1 1 0 1 1 1 0 1 1 0 1 0 1 0 1 0 1

[0082] and

[0083] 0 1 1 1 1 1 1 1 0 1 0 1 0 1 0 1 1 1 1 1 1 0 1 1 0 1 0 1 0 1 0 1 0 0 0 0 0 0 0 0 1 0 1 0 1 0 1 0 0 1 0 0 0 1 0 0 0 0 1 0 1 0 1 0

[0084] where the former is the halftone image output for given image channel 0; the latter is the halftone image output for given image channel 1. The given image is processed by two threshold matrices of two printing channels respectively, i.e. two halftone images of two channels are obtained. The size of the given image is 8x8, and the bit depth is 6, and each pixel value is 31 (close to 50% gray value). The output halftone image is 1-bit, where 1 represents inked, and 0 represents un-inked. It can be seen that the inked dots of the halftone images generated by two channels do not coincide at all.

[0085] Obviously, various modifications and changes can be made to the present application without departing from the spirit and scope thereof. Accordingly, it is intended that all such modifications and changes be included within the scope of the application as defined in the following claims and their equivalents.

Claims

1. A method of modulating a multi-channel threshold matrix in multi-channel printing, characterized by, The original threshold matrix is modulated to generate different threshold matrices for different printing channels, so that different printing channels output different halftone images; The original threshold matrix is an image, and the value range of each pixel in the image is a subset of the value range of the color component of the input continuous tone image; The process of modulating the original threshold matrix to generate different threshold matrices for different printing channels includes the following steps: Step S1 : Copy K identical threshold matrices from the original threshold matrix of the print channel, denoted as: Th0..., Th k ,...,Th K-1 ; Step S2: adding D x k to the value of each pixel point of the obtained threshold matrix Th k , wherein 1<=k<K; D is the upper limit of the pixel value range of the input contone image; and K is the number of printing channels. Step S3: calculating the pixel point coordinate set sequence Ω Th (1),...,Ω Th (kd),...,Ω Th (K×D), wherein Ω Th (kd) represents a set of pixel point coordinates whose values are kd in all pixel points in the threshold matrix Th0...Th K-1 ; 1<kd<=K×D; Step S4: all elements in the set Ω Th (kd) are assigned to the threshold matrix, each element only once; and the value of the pixel point of the corresponding coordinate is assigned as wherein represents rounding up; Any pixel point in any threshold matrix is assigned a value only once, thereby obtaining K different threshold matrices for each printing channel; In the process of modulating the original threshold matrix to generate different threshold matrices for different printing channels: First, the intersection of the set of pixel points with the same value in the threshold matrices of any two different printing channels is an empty set; Second, let the number of printing channels be K, and the value range of the pixels of the input continuous tone image be 0-D. For a coordinate point in the threshold matrix of a printing channel, the value of the pixel in the threshold matrix at the coordinate point is a. If a×K is less than or equal to D, then the intersection of the set of all pixel points with a value less than or equal to a in the threshold matrices used by any two different printing channels is an empty set. Third, the different threshold matrices of the multiple printing channels still maintain the properties of the original threshold matrix.

2. The method of claim 1, wherein the modulation of the multi-channel threshold matrix in multi-channel printing is characterized by, The method used in step S4 is to generate each channel threshold matrix in the order of channels 0 to K-1 and pixel values 1 to D; Specifically: when Ω Th (kd) is not empty, T (kmodK) is assigned to all corresponding pixel points in the Ω T (kd) set where kd represents the pixel value currently processed in the original threshold matrix.

3. The method of claim 1, wherein the modulation of the multi-channel threshold matrix in multi-channel printing is characterized by, The different threshold matrices of the multiple printing channels still maintain the properties of the original threshold matrix, that is, the distribution of the union of all pixels with a value less than or equal to a certain value in the threshold matrices generated for the multiple channels from the original threshold matrix maintains the characteristics of the original threshold matrix.