JP2004242085A - Device and method for processing image - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image processor and an image processing method capable of obtaining an output image with excellent image quality by enhancing the reproducibility of a highlighted part and improving a tone jump. <P>SOLUTION: A color space converting part 2 converts color space of image data inputted from an image inputting part 1, a first gradation correction processing part 3 performs gradation correction of the image data in accordance with a TRC, and a screen processing part 4 performs screen processing of the image data subjected to the gradation correction. A second gradation correction processing part 5 calculates the width (hereinafter called pulse width) of a pulse generated by a pulse width modulating part 6 about data by n-ary coding in the screen processing part 4, and performs gradation correction processing for expanding pulse width that is narrower than a preset threshold when the calculated pulse width is narrower than the threshold. A pulse width modulating part 6 generates a pulse and sends the generated pulse to an image outputting part 7, and the image outputting part 7 outputs image data on the basis of the pulse. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an image processing apparatus and method, and more particularly, to an image processing apparatus and method for performing tone correction to obtain an output image with good image quality.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, in copiers and printers of an electrophotographic system, etc., multi-valued image data input by an image input unit is subjected to screen processing, thereby converting the data to binary or multi-valued image data, and performing the conversion processing. A general procedure is to send image data to an image output unit. Here, the image data converted into multi-valued image data can provide richer gradation expression than the image data converted into binary image data.
[0003]
Here, the output image reproduced on the paper is linear with respect to the input image data due to restrictions caused by the image output device such as a response characteristic or a phenomenon characteristic of a ROS (Raster Output Scanner). However, problems such as poor reproduction of the highlight portion or tone jump often occur.
[0004]
As shown in FIG. 11, in the portion 38 where the exposure pulse width in the main scanning direction is short, the optical scanning device or the developing unit of the image output device has a sufficient response as a cause of the reproduction failure of the highlight portion or the occurrence of the tone jump. Not doing so is one of the causes. Particularly, in an image output device capable of outputting multi-valued data, when the optical scanning device is turned on with a pulse width shorter than one pixel width, poor reproduction of a highlight portion or tone jump occurs. The tendency of occurrence is remarkable.
[0005]
As a countermeasure for this problem, it is general to perform tone correction based on TRC (Tone Reproduction Curve: tone reproduction characteristic curve).
[0006]
In addition, in the quantization processing in the multi-level error diffusion processing, in order to eliminate instability of isolated low-density dot reproduction, quantization is performed in block units to process large dots. (For example, refer to Patent Document 1).
[0007]
[Patent Document 1]
JP-A-5-83531
[Problems to be solved by the invention]
However, according to the measures described above, the original gradation of the input image data is impaired, and the tone jump is not completely improved, so that it is difficult to obtain an output image with good image quality.
[0008]
Accordingly, it is an object of the present invention to provide an image processing apparatus and method capable of improving the reproducibility of a highlight portion and improving a tone jump to obtain an output image of good image quality. .
[0009]
[Means for Solving the Problems]
In order to achieve the above object, an invention according to claim 1 is an image processing apparatus that processes image data representing a gradation and outputs the processed image data to an image output device. Screen processing means for converting to image data, pulse width detection means for detecting a pulse width of a pulse signal in a main scanning direction having a length corresponding to the gradation of the image data converted by the screen processing means, and the pulse width When the pulse width detected by the detection unit is smaller than a preset threshold value, a correction unit that corrects the image data so as to widen the pulse width is provided.
[0010]
Further, according to a second aspect of the present invention, in the first aspect of the present invention, the correction means includes a correction table for setting a correction pulse width for a pulse width smaller than the threshold, and based on the correction table, It is characterized by correction.
[0011]
According to a third aspect of the present invention, in the second aspect of the present invention, the correction means includes a correction table creating means for creating a correction table according to a response characteristic of the image output device.
[0012]
According to a fourth aspect of the present invention, there is provided an image processing apparatus for processing image data expressing gradation and outputting the processed image data to an image output device, wherein the image data is converted into image data of a multi-value screen. A screen processing unit and a pixel value indicating a pulse width of a pulse signal in a main scanning direction having a length corresponding to a gradation of the image data is set for pixels constituting image data converted by the screen processing unit. A pixel value setting unit, a pixel value detection unit that focuses attention on the pixel along the main scanning direction, and detects a pixel value of the pixel of interest, a pixel value of the pixel detected by the pixel value detection unit, When a pulse width indicated by a pixel value of a pixel adjacent to the pixel is smaller than a preset threshold value, the image processing apparatus further includes a correction unit that corrects the image data so as to increase the pulse width.
[0013]
According to a fifth aspect of the present invention, in the fourth aspect of the present invention, the screen processing means includes a threshold value generating a threshold value matrix in which a peak of the pulse signal is shifted to the left or right side of all pixels constituting the image data. The image processing apparatus further includes a matrix generation unit that converts the image data into image data of a multi-value screen based on the threshold matrix.
[0014]
According to a sixth aspect of the present invention, in the fifth aspect of the present invention, when the pulse width indicated by the pixel value of the pixel detected by the pixel value detecting section is smaller than a threshold value, the correcting section outputs the pulse of a pixel adjacent to the pixel. When the signal peak is discontinuous with the pulse signal peak of the pixel, the image data is corrected.
[0015]
Further, according to a seventh aspect of the present invention, in the fourth aspect of the present invention, the correction means includes a correction table for setting a correction pulse width for a pulse width smaller than the threshold, and based on the correction table, It is characterized by correction.
[0016]
According to an eighth aspect of the present invention, in the invention of the seventh aspect, the correction means includes a correction table creation means for creating a correction table according to a response characteristic of the image output device.
[0017]
According to a ninth aspect of the present invention, there is provided an image processing method for processing image data expressing gradation and outputting the processed image data to an image output device, wherein the image data is converted into image data of a multi-value screen. Detecting the pulse width of the pulse signal in the main scanning direction having a length corresponding to the gradation of the converted image data, and expanding the pulse width if the detected pulse width is smaller than a preset threshold. And correcting the image data.
[0018]
According to a tenth aspect of the present invention, in the ninth aspect, the image data is corrected based on a correction table for setting a correction pulse width for a pulse width smaller than the threshold.
[0019]
An eleventh aspect of the present invention is characterized in that, in the tenth aspect of the present invention, a correction table corresponding to a response characteristic of the image output device is created.
[0020]
According to a twelfth aspect of the present invention, in the image processing method for processing image data expressing gradation and outputting the processed image data to an image output device, the image data is converted into image data of a multi-value screen. A pixel value indicating a pulse width of a pulse signal in a main scanning direction having a length corresponding to the gradation of the image data is set for a pixel constituting the converted image data, and the pixel is set in the main scanning direction. And the pixel value of the pixel of interest is detected. If the pulse width indicated by the pixel value of the detected pixel and the pixel value of the pixel adjacent to the pixel is smaller than a preset threshold, the pulse The image data is corrected so as to increase the width.
[0021]
According to a thirteenth aspect of the present invention, in the twelfth aspect of the present invention, a threshold matrix in which the peak of the pulse signal is shifted to the left or right of all the pixels constituting the image data is generated. And converting the image data into image data of a multi-value screen based on the image data.
[0022]
According to a fourteenth aspect, in the thirteenth aspect, when the pulse width indicated by the pixel value of the pixel is smaller than a threshold, the peak of the pulse signal of the pixel adjacent to the pixel is set to the peak of the pulse signal of the pixel. When the image data is discontinuous, the image data is corrected.
[0023]
The invention of claim 15 is the invention of claim 12, wherein the image data is corrected based on a correction table for setting a correction pulse width for a pulse width smaller than the threshold.
[0024]
The invention of claim 16 is the invention of claim 15, wherein a correction table according to a response characteristic of the image output device is created.
[0025]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, a first embodiment of an image processing apparatus and method according to the present invention will be described in detail with reference to the accompanying drawings.
[0026]
FIG. 1 is a block diagram illustrating an example of a functional configuration of the image processing apparatus according to the first embodiment.
[0027]
As shown in FIG. 1, the image processing apparatus includes an image input unit 1, a color space conversion unit 2, a first gradation correction processing unit 3, a screen processing unit 4, a second gradation correction processing unit 5, a pulse width It comprises a modulator 6 and an image output unit 7.
[0028]
Here, the image input unit 1 includes a sensor for reading a document, and reads an image. In the present embodiment, an example of a configuration in which color separation into three primary colors of R (red), G (green), and B (blue) and reading are performed will be described.
[0029]
The color space conversion unit 2 applies LUT (Look Up Table) to the image data of each color R, G, and B input from the image input unit 1 to output C (cyan) and M (magenta). , Y (yellow) and K (black) image data.
[0030]
In addition, the first tone correction processing unit 3 includes a TRC (Tone Reproduction Curve: tone reproduction) in which image forming conditions for compensating for a defect of the image forming method of the image output unit 7 or increasing an allowable range are set. The gradation correction of the image data is performed according to the characteristic curve.
[0031]
Further, the screen processing unit 4 performs a screen process using a screen including a predetermined threshold matrix on the image data on which the tone correction has been performed in the first tone correction processing unit 3, and performs a binary or n-valued process. (N is an integer of 3 or more).
[0032]
Further, the second gradation correction processing unit 5 performs a gradation correction process on the data that has been converted into the n-value data in the screen processing unit 4. The gradation correction processing performed by the second gradation correction processing unit 5 is based on image data and tag data accompanying the image data (determining whether the pulse is shifted to the left, center, or right). A pulse width (hereinafter, referred to as a pulse width) of the pulse generated by the pulse width modulation unit 6 is obtained. If the obtained pulse width is smaller than a preset threshold, the pulse width narrower than the threshold is widened. This is a process for performing tone correction.
[0033]
In addition, the pulse width modulation unit 6 generates a pulse represented by a change in the light emission time of a one-dot light source according to the gradation to express the gradation of the image data, and outputs the generated pulse to the image output unit 7. send.
[0034]
The image output unit 7 includes a ROS (Raster Output Scanner: optical scanning device) and a photoconductor, and the ROS scans and exposes a modulated light beam based on a pulse sent from the pulse width modulation unit 6. Then, an electrostatic latent image is formed on the charged photoconductor, and the electrostatic latent image formed on the photoconductor is copied by fixing toner on paper or the like.
[0035]
FIG. 2 is a diagram illustrating in detail the image data 8 on which the screen processing has been performed. 2A is a diagram illustrating an example of the image data 8 on which the screen processing has been performed, and FIG. 2B is a diagram illustrating the image data illustrated in FIG. 2A generated by the pulse width modulation unit 6. FIG. 9 is a diagram showing pulses of a pixel group 9 of 8;
[0036]
As shown in FIG. 2A, a screen pattern 10 corresponding to the gradation exists in the image data 8 on which the screen processing has been performed, and a pixel group 9 of the image data 8 includes a part of the screen pattern 10. Are present in the pattern A11 and the pattern B12.
[0037]
Here, as shown in FIG. 2B, the pulse of the pixel group 9 generated by the pulse width modulator 6 has a peak indicating the existence of the pattern A11 and a peak indicating the existence of the pattern B12. Although the ROS of the image output unit 7 sufficiently responds to the peak pulse width indicating the presence of the pattern B12, the ROS may not respond to the peak pulse width indicating the presence of the pattern B12.
[0038]
Therefore, the second gradation correction processing unit 5 sets a threshold of the pulse width of the peak in advance, and indicates the existence of the screen pattern 10 and a part of the screen pattern (pattern A11, pattern B12) based on the image data 8. The pulse width of the peak is determined, and if there is a pulse width of the peak narrower than the threshold, an image in which the screen pattern 10 indicated by the pulse width of the peak narrower than the threshold and a part of the screen pattern (pattern A11, pattern B12) exists A gradation correction process is performed on the data to correct the peak pulse width to which the ROS may not respond to a pulse width large enough for the ROS to respond. When setting the threshold value of the peak pulse width, it is preferable to set a value according to the characteristics of the image output unit 7.
[0039]
FIG. 3 is a diagram illustrating a correction graph 13 based on when the second gradation correction processing unit 5 performs the gradation correction processing on the image data 8.
[0040]
In the correction graph 13 shown in FIG. 3, the horizontal axis is the input pulse width (unit: μm), the vertical axis is the correction pulse width (unit: μm), and the threshold of the peak pulse width is 25.4 μm (for one pixel of 600 dpi). In the range of 0 ≦ input pulse width <25.4, the input pulse width is converted into a correction pulse width of a width enough for the ROS to respond, and in the range of 25.4 ≦ input pulse width, The input pulse width and the correction pulse width are converted to the same value (that is, a direct proportional graph is obtained). In the range of 0 ≦ input pulse width <25.4, it is preferable to set the correction graph 13 according to the characteristics of the image output unit 7.
[0041]
For example, in the gradation correction processing based on the correction graph 13 in FIG. 3, the correction pulse width D for an input pulse width C of less than 25.4 μm is converted into a value larger than the input pulse width C (C <D). , 25.4 μm or more, the correction pulse width B is converted to the same value as the input pulse width A (A = B).
[0042]
FIG. 4 is a diagram for explaining in detail the gradation correction processing performed by the second gradation correction processing unit 5 based on the correction graph. FIG. 4A is a diagram showing the image data (6 × 6) 14 before the gradation correction process, and FIG. 4B is a diagram showing the image data 18 after the gradation correction process. .
[0043]
In the image data 14 shown in FIG. 4A, a screen pattern 15 corresponding to the gradation exists. Here, in the second gradation correction processing unit 5, the threshold of the pulse width of the peak is set to the width of one pixel, and the screen pattern 15 and a part of the screen pattern are obtained from the image data 14 shown in FIG. The pulse width of the peak indicating the presence is detected, and the pulse width of the peak indicating the pattern C16, which is a part of the screen pattern, is wider than the threshold, and the pulse width of the peak indicating the pattern D17, which is a part of the screen pattern, is higher than the threshold. Narrows. Therefore, the second gradation correction processing unit 5 performs gradation correction processing on the image data 14 to correct the pulse width of the peak indicating the pattern D17 narrower than the threshold, based on the correction graph.
[0044]
As shown in FIG. 4B, the width of the pattern D'19 of the image data 18 after the gradation correction processing is larger than the width of the pattern D17 of the image data 14 before the gradation correction processing shown in FIG. It is getting wider.
[0045]
Next, the procedure of the tone correction process performed by the second tone correction processing unit 5 will be described with reference to the flowchart shown in FIG.
[0046]
The n-valued image data screen-processed by the screen processing unit and the tag data accompanying the image data are received (step S501). If n ≧ 3 (three or more image data) (YES in step S502), the image Based on the data and the tag data, a pulse of the image data generated by the pulse width modulation unit is obtained (step S503). If the obtained pulse has a peak (YES in step S504), the pulse width of the peak is equal to or less than a preset threshold. (YES in step S505), the image data is subjected to gradation correction processing for increasing the pulse width of the peak equal to or smaller than the threshold value (step S506), and the corrected image data and tag data are sent to the pulse width modulation unit (step S506). Step S507), the processing procedure ends.
[0047]
If n = 2 (binary image data) in step S502 (NO in step S502), the image data and the tag data are sent to the pulse width modulation unit without obtaining the pulse (step S507), and the processing procedure is performed. To end.
[0048]
If there is no peak in the obtained pulse in step S504 (NO in step S504), image data and tag data are sent to the pulse width modulation unit (step S507), and the processing procedure ends.
[0049]
If the pulse width of the peak is equal to or larger than the preset threshold value in step S505 (NO in step S505), the image data and the tag data are sent to the pulse width modulation unit without correcting the image data (step S507). The processing procedure ends.
[0050]
Therefore, by performing such a correction, the pulse width of the peak at which the ROS may not respond can be corrected to a pulse width long enough for the ROS to respond.
[0051]
Next, a second embodiment of the image processing apparatus and method according to the present invention will be described in detail with reference to the accompanying drawings.
[0052]
Note that the functional configuration of the image processing apparatus according to the second embodiment is similar to that of the block diagram illustrated in FIG. 1, and thus detailed description is omitted.
[0053]
However, when the main scanning direction is from the left side to the right side of the image data, the screen processing unit 4 limits the peak of the pulse of all the pixels constituting the image data to a threshold matrix in which the peak is shifted to the left side of the pixel. To a binary or n-valued (n is an integer of 3 or more) image data by performing a screen process using a screen including a limited threshold matrix. Here, when the image data is converted into n-valued image data, n pixel values indicating the growth order are assigned to each pixel.
[0054]
FIG. 6 is a diagram for explaining in detail the allocation of pixel values when converted to quinary image data.
[0055]
As shown in FIG. 6, since one pixel is divided into four in the quinary image data, a pixel value is assigned to each divided small element (for example, 0, 1, 2, 3, 4). In this embodiment, an example of a configuration in which quinary image data is used and pixel values are assigned as shown in FIG. 6 will be described.
[0056]
FIG. 7 is a diagram illustrating in detail image data on which screen processing has been performed. FIG. 7A is a diagram illustrating an example of quinary image data 20 that has been subjected to screen processing, and FIG. 7B is a diagram illustrating an example of FIG. 7A generated by the pulse width modulation unit 6. FIG. 7C is a diagram showing a pulse of a pixel group A21 of the image data 20 shown in FIG. 7C. FIG. 7C is a graph showing a pulse of a pixel group B22 of the image data 20 shown in FIG. It is.
[0057]
As shown in FIG. 7A, since the main scanning direction is from the left side to the right side of the image data 20, the peaks of the pulses of all the pixels constituting the image data are set to a threshold matrix limited so as to approach the left side of the pixel. In the image data 20 on which the screen processing has been performed, there is a screen pattern 23 that is shifted to the left of the pixel.
[0058]
Here, when attention is paid to the pixels of the pixel group A21 and the pixel group B22 of the image data 20 in the order of the main scanning direction, the pixel group A21 has a pattern E24 which is a part of the screen pattern 23, and the pixel group B22 has the screen E24. There is a pattern F25 which is a part of the pattern 23.
[0059]
Here, as shown in FIG. 7B, the pulse of the pixel group A21 of the image data 20 shown in FIG. 7A generated by the pulse width modulation unit 6 has a peak indicating the presence of the pattern E24, The ROS of the image output unit 7 responds sufficiently with the peak pulse width indicating the presence of the pattern E24, but the image shown in FIG. 7A generated by the pulse width modulation unit 6 as shown in FIG. The pulse of the pixel group B22 of the data 20 has a peak indicating the presence of the pattern F25, and the ROS may not respond with the pulse width of the peak indicating the presence of the pattern F25.
[0060]
Accordingly, the second gradation correction processing unit 5 focuses on the pixels constituting the quinary image data one by one along the main scanning direction, and sets the pixel value of the focused pixel (hereinafter referred to as a focused pixel). When the pixel value of the target pixel is 1, 2, or 3, the pixel value of the left pixel adjacent to the target pixel (hereinafter, referred to as an adjacent pixel) is checked, and the checked pixel values are 0, 1, and 2. If the number is 2, 3, the gradation correction process is performed on the target pixel.
[0061]
This is because there is a possibility that the ROS may not respond because the peak pulse width of the pixel whose pixel value is 1, 2, or 3 is smaller than the pulse width corresponding to one pixel. However, if the pixel value of the adjacent pixel is 4, all the pulses of the adjacent pixel have a peak, so that the pulse shape is the same as the pulse shape shown in FIG. Is wider than the pulse width corresponding to one pixel, the ROS responds sufficiently. If the pixel value of the adjacent pixel is 0, 1, 2, or 3, the pulse on the right side of the adjacent pixel does not have a peak, and thus has the same shape as the pulse shown in FIG. Is smaller than the pulse width corresponding to one pixel, the ROS may not respond.
[0062]
Accordingly, when the pixel value of the target pixel is 1, 2, 3 and the pixel values of the adjacent pixels are 0, 1, 2, 3, the pulse width of the peak of the pulse of the target pixel to which the ROS may not respond , The ROS performs a tone correction process for correcting the pulse width to a length sufficient to respond sufficiently.
[0063]
In the above embodiment, the configuration in which the threshold of the pulse width of the pulse peak is set to the pulse width corresponding to one pixel has been described as an example. However, the threshold corresponding to the characteristics of the image output unit 7 may be set. Is preferred.
[0064]
FIG. 8 is a diagram illustrating a correction table and a correction graph based on when the second gradation correction processing unit 5 performs the gradation correction processing on the image data. FIG. 8A is a diagram illustrating an example of a correction table 26 based on performing a gradation correction process on quinary image data, and FIG. FIG. 14 is a diagram illustrating an example of a correction graph 27 based on performing a tone correction process.
[0065]
In the gradation correction processing based on the correction table 26 shown in FIG. 8A, the pixel of interest having a pixel value of 1 is corrected to a pixel value of 3, and the pixel of interest having a pixel value of 2 is corrected to a pixel value of 3. The pixel of interest having a pixel value of 3 is corrected to have a pixel value of 4.
[0066]
The correction graph 27 shown in FIG. 8B is a graph of the correction table 26 shown in FIG. 8A. The horizontal axis represents the pixel value of interest, and the vertical axis represents the correction pixel value. In the gradation correction process, the target pixel having a small pixel value is corrected to a large pixel value, and only a small amount of correction is performed as the pixel value increases.
[0067]
It is preferable to set a correction table 26 and a correction graph 27 according to the characteristics of the image output unit 7.
[0068]
FIG. 9 is a diagram for explaining in detail a gradation correction process performed by the second gradation correction processing unit 5 based on the correction table 26 and the correction graph 27. Note that FIG. 9A is a diagram illustrating image data (6 × 6) 28 before the gradation correction process, and FIG. 9B is a diagram illustrating image data after the gradation correction process. Note that the image data shown in FIGS. 9A and 9B has n values, and as shown in FIG. 6, n pixel values (0, 1,... Allocate.
[0069]
In the image data 28 shown in FIG. 9A, a screen pattern 29 corresponding to the gradation exists. Here, in the second gradation correction processing unit 5, the threshold of the pulse width of the peak is set to the width of one pixel, and the pixel value of each pixel is obtained from the image data 28 shown in FIG.
[0070]
For example, since the pixel value of the pixel B31 of the image data 28 shown in FIG. 9A is not 0 or n-1, the pixel value of the pixel A30 which is a pixel adjacent to the pixel B31 is checked, and the pixel value of the pixel A30 is Since it is n-1, the pulse width of the peak of the continuous pulse in the pixel A30 and the pixel B31 is wider than the threshold, and therefore, the gradation correction process is not performed on the pixel B31. Further, since the pixel value of the pixel D33 of the image data 28 shown in FIG. 9A is not 0 or n−1, the pixel value of the pixel C32 which is a pixel adjacent to the pixel D33 is checked, and the pixel value of the pixel C32 is Since the pulse width is 0, the pulse width of the peak of the continuous pulse between the pixel C32 and the pixel D33 is narrower than the threshold value. Therefore, the second gradation correction processing unit 5 increases the pulse width of the peak of the pixel D33. Is performed on the pixel D based on the correction table 26 or the correction graph 27.
[0071]
As shown in FIG. 9B, the width of a part 37 of the screen pattern existing in the pixel D36 of the image data 35 after the gradation correction processing is changed to the image data before the gradation correction processing shown in FIG. The width is larger than the width of a part 34 of the screen pattern existing in the 28 pixels D33.
[0072]
Next, the procedure of the tone correction processing performed by the second tone correction processing unit 5 will be described with reference to the flowchart shown in FIG. The main scanning direction is from the left side to the right side of the image data, and is limited to a threshold matrix in which the peaks of the pulses of all the pixels constituting the image data are shifted to the left side of the pixel. In the case of data, as shown in FIG. 6, n pixel values (0, 1,..., N−1) are assigned to one pixel.
[0073]
The n-valued image data screen-processed by the screen processing unit and the tag data attached to the image data are received (step S1001). If n ≧ 3 (three-valued or more image data) (YES in step S1002), Attention is paid to the pixel along the scanning direction (step S1003), and the pixel value of the pixel of interest is obtained based on the image data and tag data (step S1004). If the pixel value of the pixel of interest is not 0 or n−1 (step S1005) If the pixel value of the adjacent pixel is not n-1 (NO in step S1006), tone correction processing is performed on the pixel of interest based on the correction table or the correction graph (step S1007), and attention is paid to all pixels. Is not completed (NO in step S1008), the process returns to step S1003.
[0074]
If attention has been paid to all pixels (YES in step S1008), the corrected image data and tag data are sent to the pulse width modulator (step S1009), and the processing procedure ends.
[0075]
If n = 2 (binary image data) in step S1002 (NO in step S1002), the image data and the tag data are sent to the pulse width modulator without paying attention to the pixels (step S1009), and the processing is performed. End the procedure.
[0076]
If the pixel value of the target pixel is 0 or n−1 in step S1005 (YES in step S1005), the process advances to step S1008.
[0077]
In step S1006, when the pixel value of the adjacent pixel is n-1 (YES in step S1006), the process proceeds to step S1008.
[0078]
Therefore, by performing such a correction, the gradation correction process can be further simplified.
[0079]
In the above embodiment, the main scanning direction is set from the left side to the right side of the image data, and the configuration is limited to a configuration using a threshold matrix in which the peaks of the pulses of all the pixels are shifted to the left side. The present invention is also applicable to a configuration using a threshold matrix shifted to the right.
[0080]
Further, in both the first and second embodiments, a configuration using an exposure device using a semiconductor laser (LD) has been described as an example, but a configuration using an exposure device using an emitting diode (LED) is also applicable. However, in the case of the configuration using the exposure device using the emitting diode, the image data 8 shown in FIG. 2A and the image data 20 shown in FIG. The tone correction process performed by the unit is the same as in the above embodiment.
[0081]
【The invention's effect】
As described above, according to the embodiments of the present invention, it is possible to improve the reproducibility of the highlight portion and improve the tone jump, thereby obtaining an output image with good image quality.
[Brief description of the drawings]
FIG. 1 is a block diagram illustrating an example of a functional configuration of an image processing apparatus according to a first embodiment.
FIG. 2 is a diagram illustrating in detail image data 8 on which screen processing has been performed.
FIG. 3 is a diagram showing a correction graph based on when a second gradation correction processing section performs gradation correction processing on image data.
FIG. 4 is a diagram illustrating in detail a gradation correction process performed by a second gradation correction processing unit based on a correction graph.
FIG. 5 is a flowchart illustrating a procedure of a tone correction process performed by a second tone correction processing unit 5;
FIG. 6 is a diagram for explaining in detail the allocation of pixel values when converted to quinary image data.
FIG. 7 is a diagram for explaining in detail image data on which screen processing has been performed;
FIG. 8 is a diagram illustrating a correction table and a correction graph based on when a second gradation correction processing unit performs a gradation correction process on image data.
FIG. 9 is a diagram illustrating in detail a gradation correction process performed by a second gradation correction processing unit based on a correction table and a correction graph.
FIG. 10 is a flowchart illustrating a procedure of a tone correction process performed by a second tone correction processing unit 5;
FIG. 11 is a diagram for explaining in detail reproduction failure of a highlight portion or a cause of occurrence of a tone jump;
[Explanation of symbols]
1 Image input section
2 Color space conversion unit
3 First gradation correction processing unit
4 Screen processing unit
5 Second tone correction processing unit
6 Pulse width modulator
7 Image output section
8 Screened image data
9 pixel group
10. Screen pattern
11 Pattern A
12 Pattern B
13 Correction graph
14 Image data before gradation correction processing
15 Screen pattern
16 Pattern C
17 Pattern D
18 Image data after gradation correction processing
19 Pattern D '
20 5-valued image data after screen processing
21 Pixel group A
22 Pixel group B
23 Screen pattern
24 Pattern E
25 Pattern F
26 Correction table
27 Correction graph
28 Image data before gradation correction processing
29 screen pattern
30 pixels A
31 Pixel B
32 pixels C
33 pixels D
34 Part of screen pattern
35 Image data after gradation correction processing
36 pixels D
Part of 37 screen pattern
38 Short exposure pulse width in main scanning direction

Claims (16)

In an image processing device that processes image data expressing gradation and outputs the processed image data to an image output device,
Screen processing means for converting the image data into image data of a multi-value screen,
Pulse width detection means for detecting the pulse width of the pulse signal in the main scanning direction having a length corresponding to the gradation of the image data converted by the screen processing means,
When the pulse width detected by the pulse width detection means is smaller than a preset threshold value, the image processing apparatus further comprises correction means for correcting the image data so as to increase the pulse width. The correction means,
A correction table for setting a correction pulse width for a pulse width smaller than the threshold,
2. The image processing apparatus according to claim 1, wherein the image data is corrected based on the correction table. The correction means,
3. The image processing apparatus according to claim 2, further comprising a correction table creating unit that creates a correction table according to a response characteristic of the image output device. In an image processing device that processes image data expressing gradation and outputs the processed image data to an image output device,
Screen processing means for converting the image data into image data of a multi-value screen,
Pixel value setting means for setting, for pixels constituting image data converted by the screen processing means, a pixel value indicating a pulse width of a pulse signal in a main scanning direction having a length corresponding to the gradation of the image data When,
Pixel value detection means for noting the pixel along the main scanning direction and detecting a pixel value of the pixel of interest;
If the pulse width indicated by the pixel value of the pixel detected by the pixel value detection means and the pixel value of a pixel adjacent to the pixel is smaller than a preset threshold, the image data is corrected so as to increase the pulse width. An image processing apparatus comprising: a correction unit. The screen processing means,
The peak of the pulse signal comprises a threshold matrix generating means for generating a threshold matrix closer to the left side or the right side of all pixels constituting the image data,
The image processing apparatus according to claim 4, wherein the image data is converted into image data of a multi-value screen based on the threshold matrix. The correction means,
When the pulse width indicated by the pixel value of the pixel detected by the pixel value detecting means is smaller than a threshold, when the peak of the pulse signal of the pixel adjacent to the pixel is discontinuous with the peak of the pulse signal of the pixel, The image processing apparatus according to claim 5, wherein the image data is corrected. The correction means,
A correction table for setting a correction pulse width for a pulse width smaller than the threshold,
The image processing apparatus according to claim 4, wherein the image data is corrected based on the correction table. The correction means,
8. The image processing apparatus according to claim 7, further comprising a correction table creating unit that creates a correction table according to a response characteristic of the image output device. In an image processing method for processing image data expressing gradation and outputting the processed image data to an image output device,
Converting the image data into image data of a multi-value screen,
Detecting the pulse width of the pulse signal in the main scanning direction having a length corresponding to the gradation of the converted image data,
When the detected pulse width is smaller than a preset threshold, the image data is corrected so as to increase the pulse width. The image processing method according to claim 9, wherein the image data is corrected based on a correction table that sets a correction pulse width for a pulse width smaller than the threshold. 11. The image processing method according to claim 10, wherein a correction table corresponding to a response characteristic of the image output device is created. In an image processing method for processing image data expressing gradation and outputting the processed image data to an image output device,
Converting the image data into image data of a multi-value screen,
For the pixels constituting the converted image data, set a pixel value indicating the pulse width of the pulse signal in the main scanning direction having a length corresponding to the gradation of the image data,
Paying attention to the pixels along the main scanning direction,
Detecting the pixel value of the noted pixel,
When the pulse width indicated by the pixel value of the detected pixel and the pixel value of the pixel adjacent to the pixel is smaller than a preset threshold, the image data is corrected so as to increase the pulse width. Image processing method. The peak of the pulse signal generates a threshold matrix shifted to the left or right side of all the pixels constituting the image data,
The image processing method according to claim 12, wherein the image data is converted into image data of a multi-value screen based on the generated threshold matrix. When the pulse width indicated by the pixel value of the pixel is smaller than a threshold, when the peak of the pulse signal of a pixel adjacent to the pixel is discontinuous with the peak of the pulse signal of the pixel, the image data is corrected. 14. The image processing method according to claim 13, wherein: 13. The image processing method according to claim 12, wherein the image data is corrected based on a correction table for setting a correction pulse width for a pulse width smaller than the threshold. 16. The image processing method according to claim 15, wherein a correction table according to a response characteristic of the image output device is created.

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