CN109727232B - Method and apparatus for detecting dot area ratio of printing plate - Google Patents
Method and apparatus for detecting dot area ratio of printing plate Download PDFInfo
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Abstract
The invention discloses a method and a device for detecting the dot area rate of a printing plate, wherein the method comprises the following steps: collecting a dot image of a printing plate; carrying out graying processing on the dot image to generate a grayscale image; binarizing the gray level image to generate a binarized image; filtering the binary image to generate a filtered image; and calculating the ratio of the number of the pixels representing the dots in the filtered image to the total number of the pixels in the filtered image to obtain the dot area rate of the printing plate. The invention reduces the complexity of the detection of the area rate of the printing dots of the printing plate, improves the detection speed and saves the time. In addition, the invention is beneficial to the miniaturization and the portability of the detection system of the dot area rate, and can be conveniently applied to the field proofing and verification of a flexographic printing system.
Description
Technical Field
The invention belongs to the technical field of printing plate dot area rate detection, and particularly relates to a method and equipment for detecting the dot area rate of a printing plate.
Background
At present, in the process of calculating the area ratio of printing plate dots, a camera is often adopted to collect the image of the printing plate dots, and then the image of the printing plate dots is transmitted to a large-scale workstation for calculation. Because the large-scale workstation is huge in size, inconvenient to operate, complex in operation and high in cost, the scheme is difficult to apply to field proofing and verification of a flexographic printing system, and the area rate of the printing plate dot cannot be given in real time.
Disclosure of Invention
The technical problem to be solved by the embodiment of the invention is to provide a method and equipment for detecting the area rate of printing dots, aiming at overcoming the defects of high calculation cost and inconvenient operation of the area rate of printing dots in the prior art.
The embodiment of the invention solves the technical problems through the following technical scheme:
the embodiment of the invention provides a method for detecting the area rate of dots of a printing plate, which comprises the following steps:
s1, collecting a dot image of a printing plate;
s2, carrying out gray processing on the dot image to generate a gray image;
s3, binarizing the gray level image to generate a binarized image;
s4, filtering the binary image to generate a filtered image;
and S5, calculating the ratio of the number of the pixels representing the dots in the filtered image to the total number of the pixels of the filtered image to obtain the dot area rate of the printing plate.
Preferably, the halftone dot image is an RGB color image, and the step S2 includes:
each pixel of the halftone dot image is grayed according to the following formula,
f = [0.395 × R +0.641 × G +0.234 × B +0.5], where f is a grayscale value of the pixel, R is a luminance value of a red channel of the pixel, G is a luminance value of a green channel of the pixel, and B is a luminance value of a blue channel of the pixel.
Preferably, step S3 includes:
and binarizing the gray level image by using the Otsu method.
Preferably, step S4 includes:
sequentially carrying out the following processing on each pixel of the binary image from left to right and from top to bottom:
replacing the value of the pixel with a correction value, wherein the correction value is obtained by XOR of the values of all pixels adjacent to the pixel in the binary image; the pixels adjacent to the pixel are adjacent pixels on the left, right, upper, and lower sides of the pixel.
Preferably, the pixels characterizing the dots are pixels having a value of 1.
Preferably, between step S4 and step S5, the method further comprises the steps of:
calculating the number Ni of pixels with the median value of 1 in each row of pixels of the filtered image, wherein i belongs to [1, r ], and r is the row number of the pixels of the filtered image; deleting a first line of the filtered image if the number N1 of pixels having a value of 1 of the first line is greater than 0 and less than or equal to Nj, j ∈ [2, r-1 ]; deleting the last line if the number of pixels with a value of 1 of the last line of the filtered image Nr is greater than 0 and less than or equal to Nj, j ∈ [2, r-1 ];
calculating the quantity Mk of pixels with the median value of 1 in each column of pixels of the filtered image, wherein k belongs to [1, c ], and c is the number of columns of pixels of the filtered image; deleting a first column of the filtered image if the number M1 of pixels having a value of 1 is greater than 0 and less than or equal to Mn, n ∈ [2, c-1 ]; deleting the last column of the filtered image if the number of pixels having a value of 1, mc, is greater than 0 and less than or equal to Mn, n ∈ [2, c-1 ];
outputting the cut image;
step S5 further includes: and calculating the percentage of the number of pixels with the value of 1 of the cut image to the total number of pixels of the cut image, and taking the percentage as the area rate of the printing plate dots.
The invention also provides a portable dot area rate detection device, which comprises a portable shell, an image acquisition unit, a graying processing unit, a binarization unit, a filtering unit and a dot area rate calculation unit;
the image acquisition unit is arranged on the portable shell, and the graying processing unit, the binarization unit, the filtering unit and the mesh point area rate calculation unit are arranged in the portable shell;
the image acquisition unit is used for acquiring a dot image of the printing plate;
the graying processing unit is used for performing graying processing on the dot image to generate a grayscale image;
the binarization unit is used for binarizing the gray level image to generate a binarized image;
the filtering unit is used for filtering the binary image to generate a filtered image;
the dot area rate calculating unit is used for calculating the ratio of the number of pixels representing dots in the filtered image to the total number of pixels in the filtered image so as to obtain the dot area rate of the printing plate.
Preferably, the detection device further comprises a display unit, the display unit is arranged on the outer surface of the portable shell, and the display unit is used for displaying the dot area rate of the printing plate.
Preferably, the image capturing unit includes a CMOS (Complementary Metal Oxide Semiconductor) image sensor, and the resolution of the CMOS image sensor is 500 to 2500 ten thousand pixels.
Preferably, the detection device further comprises a cutting unit, and the cutting unit is arranged inside the portable shell;
the graying processing unit is also used for performing graying processing on each pixel of the halftone dot image according to the following formula:
f = [0.395 × R +0.641 × G +0.234 × B +0.5], where f is a grayscale value of the pixel, R is a luminance value of a red channel of the pixel, G is a luminance value of a green channel of the pixel, and B is a luminance value of a blue channel of the pixel;
the binarization unit is also used for binarizing the gray level image by adopting an Otsu method;
the filtering unit is further configured to sequentially perform the following processing on each pixel of the binarized image in order from left to right and from top to bottom: replacing the value of the pixel with a correction value, wherein the correction value is the value obtained by XOR of the values of all pixels adjacent to the pixel in the binary image; the pixels adjacent to the pixel are adjacent pixels on the left side, the right side, the upper side and the lower side of the pixel;
the clipping unit is used for calculating the number Ni of pixels with the median value of 1 in each line of pixels of the filtered image, i belongs to [1, r ], wherein r is the line number of the pixels of the filtered image; deleting a first line of the filtered image if the number N1 of pixels having a value of 1 of the first line is greater than 0 and less than or equal to Nj, j ∈ [2, r-1 ]; deleting the last line if the number of pixels with a value of 1 of the last line of the filtered image Nr is greater than 0 and less than or equal to Nj, j ∈ [2, r-1 ];
the clipping unit is further used for calculating the number Mk of pixels with the median value of 1 in each row of pixels of the filtered image, wherein k belongs to [1, c ], and c is the number of the rows of pixels of the filtered image; deleting the first column of the filtered image if the number M1 of pixels having a value of 1 of the first column is greater than 0 and less than or equal to Mn, n ∈ [2, c-1 ]; deleting the last column of the filtered image if the number of pixels having a value of 1, mc, is greater than 0 and less than or equal to Mn, n ∈ [2, c-1 ];
the cutting unit is also used for outputting a cut image;
the dot area rate calculating unit is also used for calculating the percentage of the number of pixels with the value of 1 of the cut image to the total number of pixels of the cut image, and the percentage is used as the dot area rate of the printing plate.
The positive progress effects of the invention are as follows: the invention reduces the complexity of the detection of the area rate of the printing dots of the printing plate, improves the detection speed and saves the time. In addition, the invention is beneficial to the miniaturization and the portability of the detection system of the dot area rate, and can be conveniently applied to the field proofing and verification of a flexographic printing system.
Drawings
Fig. 1 is a schematic structural diagram of a portable dot area ratio detection apparatus according to embodiment 1 of the present invention.
Fig. 2 is a schematic diagram of a filtering unit of a portable dot area ratio detection apparatus according to embodiment 1 of the present invention processing pixels in a first row and a first column.
Fig. 3 is a schematic diagram of the filter unit of the portable halftone dot area ratio detection apparatus according to embodiment 1 of the present invention processing pixels in the first row and the second column.
Fig. 4 is a flowchart of a method for detecting a dot area ratio of a printing plate according to example 1 of the present invention.
Fig. 5 is a schematic structural diagram of a portable dot area ratio detection apparatus according to embodiment 2 of the present invention.
Fig. 6 is a flowchart of a method for detecting a dot area ratio of a printing plate according to embodiment 2 of the present invention.
Detailed Description
The invention is further illustrated by the following examples, which are not intended to limit the scope of the invention.
Example 1
The present embodiment provides a portable dot area ratio detection device, and referring to fig. 1, the detection device includes a portable housing (not shown in the figure), an image acquisition unit 101, a graying processing unit 102, a binarization unit 103, a filtering unit 104, and a dot area ratio calculation unit 105. The image acquisition unit 101 is disposed on the portable housing, and the graying processing unit 102, the binarization unit 103, the filtering unit 104, and the halftone dot area ratio calculation unit 105 are disposed inside the portable housing.
The image acquisition unit 101 is used for acquiring a dot image of the printing plate. The graying processing unit 102 is configured to perform graying processing on the halftone dot image to generate a grayscale image. The binarization unit 103 is used to binarize the grayscale image to generate a binarized image. The filtering unit 104 is configured to filter the binarized image to generate a filtered image. The dot area ratio calculating unit 105 is configured to calculate a ratio of the number of pixels representing dots in the filtered image to the total number of pixels in the filtered image, so as to obtain a dot area ratio of the printing plate.
When the portable dot area ratio detection device of the embodiment is used, a user can hold the detection device with hands to perform on-site proofing on a flexographic printing system, and the image acquisition unit 101 acquires dot images of a printing plate. In the present embodiment, the image capturing unit employs a CMOS image sensor having a resolution of 1000 ten thousand pixels. In other alternative embodiments, the image capturing unit may employ a CCD (charge coupled device) image sensor, and the resolution of the image capturing unit preferably ranges from 500 ten thousand pixels to 2500 ten thousand pixels.
Then, the gradation processing unit 102 performs gradation processing on the halftone dot image. In the present embodiment, the graying processing unit 102 performs graying processing on each pixel of the halftone dot image according to the following formula:
f = [0.395 × R +0.641 × G +0.234 × B +0.5], where f is a grayscale value of the pixel, R is a luminance value of a red channel of the pixel, G is a luminance value of a green channel of the pixel, and B is a luminance value of a blue channel of the pixel. The graying processing method can improve the precision of subsequent processing. And obtaining a gray image after graying.
Next, the binarization unit 103 binarizes the grayscale image to generate a binarized image. In this embodiment, the binarization unit 103 binarizes the grayscale image by using the tsu method. Each pixel in the grayscale image has a grayscale value of f, i.e., its grayscale level is f (according to f, a picture can be divided into foreground pixels and background pixels, where foreground pixels refer to all pixels whose grayscale levels are lower than or equal to t, background pixels refer to pixels greater than t, and t is a binary segmentation threshold of the foreground and the background). The proportion of foreground pixels to the total pixels of the grayscale image can be recorded as w0, the mean value of the pixel values of the foreground pixels can be recorded as u0, the proportion of background pixels to the total pixels of the grayscale image can be recorded as w1, and the mean value of the pixel values of the background pixels can be recorded as u1. The average of the pixels of the entire grayscale image is denoted as u = w0 u0+ w1 u1. Constructing an objective function g (t) = w0 ^ u 0-u) ^2+ w1 ^ u1-u ^2. And calculating g (t), wherein the corresponding t when the g (t) is maximum can be determined as the binary segmentation threshold value t. And marking the value of the pixel with the gray value larger than the binarization segmentation threshold value t in the gray image as 1, and marking the value of the pixel with the gray value not larger than the binarization segmentation threshold value t in the gray image as 0, thereby obtaining the binarization image. Through binarization processing, each pixel can be represented by only one-bit binary number, so that the computation amount of subsequent processing is greatly reduced.
Then, the filtering unit 104 filters the binarized image to generate a filtered image. In the present embodiment, the filtering unit 104 sequentially performs the following processing on each pixel of the binarized image in order from left to right and from top to bottom: replacing the value of the pixel with a correction value, wherein the correction value is obtained by XOR of the values of all pixels adjacent to the pixel in the binary image; the pixels adjacent to the pixel are pixels on the left, right, upper, and lower sides of the pixel. Fig. 2 shows a part of pixels in the upper left corner of the binarized image. During filtering, the first pixel P1 in the first row and the first column of the binarized image is processed, the left side and the upper side of the first pixel P1 have no pixel, and the adjacent pixels of the first pixel P1 are the second pixel P2 on the right side and the third pixel P3 on the lower side. If the pixel value 0 of the second pixel P2 and the pixel value 1 of the third pixel P3 are xored to obtain 1, the value of the first pixel P1 is replaced by 1 as shown in fig. 3. Then, the next pixel second pixel P2 is processed. The adjacent pixels of the second pixel P2 are the first pixel P1 on the left side thereof, the fourth pixel P4 on the right side thereof, and the fifth pixel P5 on the lower side thereof, and the exclusive or of the three results in 0, so that the value of the second pixel P2 is kept constant at 0. Then, the fourth pixel P4 is processed. When the last pixel of the first row is processed, the first pixel of the second row (third pixel P3) is processed. And repeating the steps until all pixels of the binary image are processed, and obtaining the filtered image. Through filtering, noise in the binary image is removed, and the detection precision of the dot area rate can be improved.
Next, the dot area ratio calculating unit 105 counts the number of pixels representing dots (i.e., pixels having a value of 1) in the filtered image and the total number of pixels in the filtered image, and calculates the percentage of the pixels representing dots in the filtered image to the total number of pixels in the filtered image, which is the dot area ratio of the printing plate.
The portable dot area rate detection device reduces the complexity of detecting the dot area rate of the printing plate, improves the detection speed and saves time. In addition, since the calculation complexity is reduced, the graying processing unit, the binarization unit, the filtering unit and the dot area rate calculating unit of the embodiment can be integrated in a Central Processing Unit (CPU), so that a miniaturized and portable design is realized, and the method can be conveniently applied to field proofing and verification of a flexographic printing system.
The embodiment also provides a method for detecting the dot area rate of the printing plate, which is implemented by using the portable dot area rate detection device of the embodiment, and referring to fig. 4, the method includes the following steps:
step S201, collecting a dot image of a printing plate;
step S202, carrying out gray processing on the dot image to generate a gray image;
step S203, binarizing the gray level image to generate a binarized image;
step S204, filtering the binary image to generate a filtered image;
and S205, calculating the ratio of the number of the pixels representing the dots in the filtered image to the total number of the pixels of the filtered image to obtain the dot area rate of the printing plate.
In step S201, a dot image of the printing plate is captured by the image capturing unit 101.
In step S202, the graying processing unit 102 performs graying processing on each pixel of the halftone dot image according to the following formula:
f = [0.395 × R +0.641 × G +0.234 × B +0.5], where f is a grayscale value of the pixel, R is a luminance value of a red channel of the pixel, G is a luminance value of a green channel of the pixel, and B is a luminance value of a blue channel of the pixel. The graying processing method can improve the precision of subsequent processing. And obtaining a gray image after the graying treatment.
In step S203, the binarization unit 103 binarizes the grayscale image by using the tsu method. Each pixel in the grayscale image has a grayscale value of f, i.e., its grayscale level is f (according to f, a picture can be divided into foreground pixels and background pixels, where foreground pixels refer to all pixels whose grayscale levels are lower than or equal to t, background pixels refer to pixels greater than t, and t is a binary segmentation threshold of the foreground and the background). The proportion of foreground pixels to the total pixels of the grayscale image can be recorded as w0, the mean value of the pixel values of the foreground pixels can be recorded as u0, the proportion of background pixels to the total pixels of the grayscale image can be recorded as w1, and the mean value of the pixel values of the background pixels can be recorded as u1. The average of the pixels of the entire grayscale image is denoted as u = w0 u0+ w1 u1. And constructing an objective function g (t) = w0 (u 0-u) ^2+ w1 (u 1-u) ^2. And g (t) is calculated, and the corresponding t when the g (t) is maximum can be determined as the binary segmentation threshold value t. And marking the value of the pixel with the gray value larger than the binarization segmentation threshold value t in the gray image as 1, and marking the value of the pixel with the gray value not larger than the binarization segmentation threshold value t in the gray image as 0, thereby obtaining the binarization image. Through binarization processing, each pixel can be represented by only one-bit binary number, so that the computation amount of subsequent processing is greatly reduced.
In step S204, the filtering unit 104 sequentially performs the following processing for each pixel of the binarized image in order from left to right and from top to bottom: replacing the value of the pixel with a correction value, wherein the correction value is obtained by XOR of the values of all pixels adjacent to the pixel in the binary image; the pixels adjacent to the pixel are pixels on the left, right, upper, and lower sides of the pixel. Fig. 2 shows a part of pixels in the upper left corner of the binarized image. During filtering, the first pixel P1 in the first row and the first column of the binarized image is processed, the left side and the upper side of the first pixel P1 have no pixel, and the adjacent pixels of the first pixel P1 are the second pixel P2 on the right side and the third pixel P3 on the lower side. If the pixel value 0 of the second pixel P2 and the pixel value 1 of the third pixel P3 are xored to obtain 1, the value of the first pixel P1 is replaced with 1 as shown in fig. 3. Then, the next pixel second pixel P2 is processed. The adjacent pixels of the second pixel P2 are the first pixel P1 on the left side thereof, the fourth pixel P4 on the right side thereof, and the fifth pixel P5 on the lower side thereof, and the three or three of them are xored to obtain 0, so that the value of the second pixel P2 is kept to be 0. Then, the fourth pixel P4 is processed. When the last pixel of the first row is processed, the first pixel of the second row (third pixel P3) is processed. And repeating the steps until all pixels of the binary image are processed, and obtaining the filtered image. Through filtering, the noise in the binary image is removed, and the detection precision of the area rate of the dots can be improved.
In step S205, the dot area ratio calculating unit 105 counts the number of pixels representing dots in the filtered image (i.e., pixels with a value of 1) and the total number of pixels in the filtered image, and calculates the percentage of the pixels in the filtered image, which is the dot area ratio of the printing plate.
Example 2
On the basis of the portable halftone dot area rate detection device of embodiment 1, this embodiment provides a portable halftone dot area rate detection device, and referring to fig. 2, the detection device further includes a cropping unit 106 and a display unit 107. The cutting unit 106 is provided inside the portable housing, and the display unit 107 is provided on the outer surface of the portable housing. The display unit 107 is used for displaying the dot area rate of the printing plate.
The cropping unit 106 is configured to calculate the number Ni of pixels whose median value is 1 in each row of pixels of the filtered image, where i belongs to [1, r ], where r is the row number of pixels of the filtered image; deleting a first line of the filtered image if the number N1 of pixels having a value of 1 of the first line is greater than 0 and less than or equal to Nj, j ∈ [2, r-1 ]; deleting the last line if the number of pixels with a value of 1 of the last line of the filtered image Nr is greater than 0 and less than or equal to Nj, j ∈ [2, r-1 ]; the clipping unit is further used for calculating the number Mk of pixels with the median value of 1 in each row of pixels of the filtered image, wherein k belongs to [1, c ], and c is the number of the rows of pixels of the filtered image; deleting a first column (leftmost column) of the filtered image if the number M1 of pixels having a value of 1 is greater than 0 and less than or equal to Mn, n ∈ [2, c-1 ]; deleting the last column of the filtered image (the rightmost column) if the number of pixels having a value of 1, mc, is greater than 0 and less than or equal to Mn, n ∈ [2, c-1 ]; the cropping unit is also used for outputting the cropped image. That is, the cropping unit 106 receives the filtered image output by the filtering unit 104, and calculates the number of pixels having a value of 1 in each row of pixels of the filtered image. And if the N1 is not more than the minimum one of the Nj (j epsilon [2, r-1 ]), judging that the grid at the upper edge of the filtered image is incomplete, and the reference value of the detection of the area rate of the halftone dots is low, so that the first line of the filtered image is deleted. While the first row is determined, the cropping unit 106 further determines whether the last row needs to be deleted according to a similar method, and the cropping unit 106 further determines whether the leftmost column and the rightmost column of the filtered image need to be deleted according to the foregoing method. After the determination is completed, the cropping unit 106 deletes the row or column in the filtered image that meets the deletion condition, that is, completes the cropping operation on the filtered image, and outputs the cropped image. In other optional embodiments, the cropping unit may first determine the first line and the last line of the filtered image, and then perform a corresponding deletion operation to obtain an intermediate image; and then the cutting unit judges the leftmost column and the rightmost column of the middle image, performs corresponding deletion operation and finally outputs the cut image. Or, the clipping unit may first determine the leftmost column and the rightmost column of the filtered image, and then perform a corresponding deletion operation to obtain an intermediate image; then the cutting unit judges the first line and the last line of the intermediate image, carries out corresponding deleting operation and finally outputs the cut image.
Then, the dot area ratio calculation unit 105 counts the number of pixels having a value of 1 of the clipped image and the total number of pixels of the clipped image, and calculates the percentage of the number of pixels having a value of 1 of the clipped image to the total number of pixels of the clipped image, and takes the percentage as the dot area ratio of the printing plate. By means of cutting operation, interference of incomplete grids is eliminated, and the area rate of the net points of the finally obtained printing plate is more accurate.
The display unit 107 displays the dot area ratio of the printing plate and also displays the dot image of the printing plate for reference by the user.
On the basis of the method for detecting the area rate of printing dots of the printing plate in embodiment 1, this embodiment further provides a method for detecting the area rate of printing dots of a printing plate, which is implemented by using the portable apparatus for detecting the area rate of printing dots in this embodiment, and with reference to fig. 6, the method includes the following steps:
step S201, collecting a dot image of the printing plate.
Step S202, carrying out gray processing on the dot image to generate a gray image.
Step S203 binarizes the grayscale image to generate a binarized image.
And step S204, filtering the binary image to generate a filtered image.
And step S2041, judging whether the edge of the filtered image meets the deleting condition, if so, deleting, and outputting the cut image.
Step S205 includes step S2051 of calculating the percentage of the number of pixels having a value of 1 of the cropped image to the total number of pixels of the cropped image, as the dot area ratio of the printing plate.
And step S206, displaying the dot area rate of the printing plate.
In specific implementation, in step S2041, the clipping unit 106 calculates the number Ni of pixels whose median value is 1 in each row of pixels of the filtered image, where i belongs to [1, r ], where r is the row number of pixels of the filtered image; deleting a first line of the filtered image if the number N1 of pixels having a value of 1 of the first line is greater than 0 and less than or equal to Nj, j ∈ [2, r-1 ]; deleting the last line if the number of pixels with a value of 1 of the last line of the filtered image Nr is greater than 0 and less than or equal to Nj, j ∈ [2, r-1 ]; the clipping unit is further used for calculating the number Mk of pixels with the median value of 1 in each column of pixels of the filtered image, wherein k belongs to [1, c ], and c is the number of the columns of the pixels of the filtered image; deleting a first column of the filtered image if the number M1 of pixels having a value of 1 is greater than 0 and less than or equal to Mn, n ∈ [2, c-1 ]; deleting the last column of the filtered image if the number of pixels having a value of 1, mc, is greater than 0 and less than or equal to Mn, n ∈ [2, c-1 ]; the cropping unit is also used for outputting the cropped image. That is, the cropping unit 106 receives the filtered image output by the filtering unit 104, and calculates the number of pixels having a value of 1 in each row of pixels of the filtered image. And if the N1 is not more than the minimum one of the Nj (j epsilon [2, r-1 ]), judging that the grid at the upper edge of the filtered image is incomplete, and the reference value of the detection of the area rate of the halftone dots is low, so that the first line of the filtered image is deleted. While the first line is judged, the cropping unit 106 also judges whether the last line needs to be deleted according to a similar method, and the cropping unit 106 also judges whether the leftmost column and the rightmost column of the filtered image need to be deleted according to the method. After the determination is completed, the cropping unit 106 deletes the row or column in the filtered image that meets the deletion condition, that is, completes the cropping operation on the filtered image, and outputs the cropped image. In other optional embodiments, the cropping unit may first determine the first line and the last line of the filtered image, and then perform a corresponding deletion operation to obtain an intermediate image; and then the cutting unit judges the leftmost column and the rightmost column of the middle image, performs corresponding deletion operation and finally outputs the cut image. Or, the clipping unit may first determine the leftmost column and the rightmost column of the filtered image, and then perform the corresponding deletion operation to obtain an intermediate image; then the cutting unit judges the first line and the last line of the intermediate image, corresponding deletion operation is carried out, and finally the cut image is output.
Then, in step S2051, the dot area ratio calculation unit 105 counts the number of pixels of the cropped image having a value of 1 and the total number of pixels of the cropped image, and calculates the percentage of the number of pixels of the cropped image having a value of 1 to the total number of pixels of the cropped image, and takes the percentage as the dot area ratio of the printing plate. By means of cutting operation, interference of incomplete grids is eliminated, and the area rate of the net points of the finally obtained printing plate is more accurate.
Finally, in step S206, the display unit 107 displays the dot area ratio of the printing plate and also displays the dot image of the printing plate for the user to refer to.
While specific embodiments of the invention have been described above, it will be appreciated by those skilled in the art that these are by way of example only, and that the scope of the invention is defined by the appended claims. Various changes and modifications to these embodiments may be made by those skilled in the art without departing from the spirit and scope of the invention, and these changes and modifications are within the scope of the invention.
Claims (8)
1. A method for detecting the dot area rate of a printing plate is characterized by comprising the following steps:
s1, collecting a dot image of the printing plate;
s2, carrying out gray processing on the dot image to generate a gray image;
s3, binarizing the gray level image to generate a binarized image;
s4, filtering the binary image to generate a filtered image;
s5, calculating the ratio of the number of pixels representing the dots in the filtered image to the total number of the pixels of the filtered image to obtain the dot area rate of the printing plate;
step S4 comprises the following steps:
sequentially carrying out the following processing on each pixel of the binary image from left to right and from top to bottom:
replacing the value of the pixel with a correction value, wherein the correction value is obtained by carrying out exclusive OR on the values of all pixels adjacent to the pixel in the binary image; the pixels adjacent to the pixels are the pixels on the left side, the right side, the upper side and the lower side of the pixels adjacent to the pixels;
between step S4 and step S5, the method further comprises the steps of:
calculating the number Ni of pixels with the value of 1 in each row of pixels of the filtered image, wherein i belongs to [1, r ], and r is the row number of the pixels of the filtered image; deleting a first line of the filtered image if the number N1 of pixels having a value of 1 of the first line is greater than 0 and less than or equal to Nj, j ∈ [2, r-1 ]; deleting the last line of the filtered image if the number of pixels having a value of 1, nr, of the last line is greater than 0 and less than or equal to Nj, j ∈ [2, r-1 ];
calculating the quantity Mk of pixels with the median value of 1 in each column of pixels of the filtered image, wherein k belongs to [1, c ], and c is the column number of the pixels of the filtered image; deleting a first column of the filtered image if the number M1 of pixels having a value of 1 of the first column is greater than 0 and less than or equal to Mn, n ∈ [2, c-1 ]; deleting the last column of the filtered image if the number of pixels having a value 1, mc, of the last column is greater than 0 and less than or equal to Mn, n ∈ [2, c-1 ];
outputting the cut image;
step S5 further includes: and calculating the percentage of the number of the pixels with the value of 1 of the cut image in the total number of the pixels of the cut image, and taking the percentage as the area ratio of the dots of the printing plate.
2. The method for detecting the dot area ratio of a printing plate according to claim 1, wherein the dot image is an RGB color image, and the step S2 includes:
graying each pixel of the dot image according to the following formula,
f = [0.395 × R +0.641 × G +0.234 × B +0.5], where f is a grayscale value of the pixel, R is a luminance value of a red channel of the pixel, G is a luminance value of a green channel of the pixel, and B is a luminance value of a blue channel of the pixel.
3. The method for detecting a dot area ratio of a printing plate according to claim 1, wherein the step S3 comprises:
and binarizing the gray level image by adopting an Otsu method.
4. The method for detecting a halftone dot area ratio of a printing plate according to claim 1, wherein said pixel representing a halftone dot is a pixel having a value of 1.
5. A portable dot area rate detection device is characterized by comprising a portable shell, an image acquisition unit, a graying processing unit, a binarization unit, a filtering unit and a dot area rate calculation unit;
the image acquisition unit is arranged on the portable shell, and the graying processing unit, the binarization unit, the filtering unit and the dot area rate calculation unit are arranged in the portable shell;
the image acquisition unit is used for acquiring a dot image of the printing plate;
the graying processing unit is used for performing graying processing on the dot image to generate a grayscale image;
the binarization unit is used for binarizing the gray level image to generate a binarized image;
the filtering unit is used for filtering the binary image to generate a filtered image;
the dot area rate calculating unit is used for calculating the ratio of the number of pixels representing dots in the filtered image to the total number of pixels in the filtered image so as to obtain the dot area rate of the printing plate;
the detection equipment further comprises a cutting unit, and the cutting unit is arranged inside the portable shell;
the filtering unit is further configured to sequentially perform the following processing on each pixel of the binarized image in order from left to right and from top to bottom: replacing the value of the pixel with a correction value, wherein the correction value is obtained by carrying out exclusive OR on the values of all pixels adjacent to the pixel in the binary image; the pixels adjacent to the pixels are the pixels on the left side, the right side, the upper side and the lower side of the adjacent pixels;
the clipping unit is used for calculating the quantity Ni of pixels with the median value of 1 in each row of pixels of the filtered image, i belongs to [1, r ], wherein r is the row number of the pixels of the filtered image; deleting a first line of the filtered image if the number N1 of pixels having a value of 1 of the first line is greater than 0 and less than or equal to Nj, j ∈ [2, r-1 ]; deleting the last line of the filtered image if the number of pixels having a value of 1, nr, is greater than 0 and less than or equal to Nj, j ∈ [2, r-1 ];
the clipping unit is further configured to calculate the number Mk of pixels having a median of 1 in each column of pixels of the filtered image, where k is [1, c ], where c is the number of columns of pixels of the filtered image; deleting a first column of the filtered image if the number M1 of pixels having a value of 1 of the first column is greater than 0 and less than or equal to Mn, n ∈ [2, c-1 ]; deleting the last column of the filtered image if the number of pixels having a value 1, mc, of the last column is greater than 0 and less than or equal to Mn, n ∈ [2, c-1 ];
the cutting unit is also used for outputting a cut image;
the dot area ratio calculating unit is further configured to calculate a percentage of the number of pixels of the cropped image having a value of 1 to the total number of pixels of the cropped image, and the percentage is used as the dot area ratio of the printing plate.
6. The apparatus of claim 5, further comprising a display unit disposed on an outer surface of the portable housing, the display unit being configured to display a dot area ratio of the printing plate.
7. The portable dot area ratio detection device according to claim 5, wherein the image capturing unit comprises a CMOS image sensor having a resolution of 500 to 2500 ten thousand pixels.
8. The portable dot area ratio detecting apparatus according to claim 5, wherein the graying processing unit is further configured to perform graying processing on each pixel of the dot image according to the following formula:
f = [0.395 × R +0.641 × G +0.234 × B +0.5], where f is a grayscale value of the pixel, R is a luminance value of a red channel of the pixel, G is a luminance value of a green channel of the pixel, and B is a luminance value of a blue channel of the pixel;
the binarization unit is also used for binarizing the gray level image by adopting Otsu method.
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