JPH01277058A - Halftone picture recorder - Google Patents

Abstract

PURPOSE:To express the halftone of an original picture with high fidelity in a fast processing by providing an influence storage means to store influence applied on another picture element neighboring to a picture element and a increment/decrement correction means to correct the increment/decrement of a threshold value decided in another picture element corresponding to the above means. CONSTITUTION:The processing of a picture recording program is started and a CPU40A clears a prescribed area in a RAM40C. Next, picture light-and-shade information H of one picture element is inputted from a picture reading part 50, and is compared with the prescribed threshold value S. When a compared result is shown as H>S, the modulation signal of laser emitting element 8 is generated when the position corresponding to the picture element irradiated by a laser beam when the laser beam is scanned on the position by a polygonal mirror 10. Meanwhile, when the compared result is shown as H<=S, no output dot is recorded, and a laser modulation signal without emitting the laser beam is generated. Thus, the processing of one picture element is completed, and when the processings for all of the picture light-and-shade information from the reading part 50 are completed, the execution of the picture recording program is finished.

Description

[Detailed Description of the Invention] Purpose of the Invention (Field of Industrial Application) The present invention compares a threshold value determined for each pixel with the density of the original image of that pixel, and generates an output dot signal according to the comparison result. The present invention relates to a halftone image recording device that records halftone images.

(Prior Art) Conventionally, in halftone image recording devices that record halftone images by hard copy, etc., methods such as the dither method, the minimum average error method, the average value restriction method, and the pixel allocation method within a mesh have been used. .

However, as is well known, the minimum average error method, the average value limit method,
Halftone image recording devices that adopt the intra-mesh pixel allocation method require a large amount of calculation to determine the output dot signal of one pixel, so an expensive control system with high processing power is indispensable. Processing takes a long time, leading to larger equipment and higher costs.

On the other hand, in the dither method, a threshold value is determined for each pixel in a minute area,
Compare that threshold with the density level of the original image for that pixel,
The output dot (presence/absence) signal of that pixel is determined and a halftone image is recorded by so-called binarization. In addition, in order to further improve the reproduction accuracy of halftones, we have adopted the so-called multi-value method, in which multiple threshold values are set for each pixel, and the output dot level signal to be displayed at each pixel is determined according to the result of comparing the density of the original image with the level of the original image. There are also devices that record halftone images. According to such a dither method, as the density level of the original image to be recorded becomes higher, the density of the output dots and/or the recording area gradually increases, and halftones are reproduced in a pseudo manner. Therefore, according to a halftone image recording apparatus that employs such a dither method, a halftone image can be recorded by simple numerical comparison, and high-speed processing can be performed using a simple control system.

(Problems to be Solved by the Invention) However, even in halftone image recording apparatuses that employ the dither method, the following problems remain unsolved.

As is clear from the above explanation, the principle of expressing pseudo halftones in the dither method is achieved by adjusting the recording dot area which increases with output dots. In other words, it is assumed that the relationship between the output dot signal and the recording area is independent for each pixel.

However, in reality, in the output section of a halftone image recording device, in the case of a laser printer, the part irradiated with laser light becomes the output dot, and in the case of a dot printer, the dot struck by a pin becomes the output dot; is approximately circular. Therefore, if we consider the case where the entire area is recorded using this circular output dot, the recording area of the output dot output to each pixel will be output so that it extends to the adjacent pixel, as shown in Figure 5. I have no choice but to set the size of the dot circle.

Therefore, by recording one output dot, the recording area expands to include pixels other than the target dot, and the premise that the relationship between the output dot signal and the recording area is independent for each pixel does not hold true.

Moreover, as the number of recorded output dots increases, the area of the overflow area increases, so when recording high-density original images, the influence of the overflow area becomes noticeable, making it impossible to maintain sufficient gradation on the high-density side. There wasn't.

The present invention has been developed in view of the above problems, and enables high-speed processing using a simple control system, and also provides a halftone image that can faithfully reproduce any original image with sufficient gradation. The purpose is to provide a recording device.

Configuration of the Invention (Means for Solving the Problems) The configuration of the halftone image recording device of the present invention that solves the above problems is as shown in the basic configuration diagram in FIG. Compare the density of that pixel with the original image, and determine the output dot signal to that pixel according to the comparison result,
In a halftone image recording device that reproduces a halftone image by adjusting the recording area using the determined output dot signal, the recording area of the pixel for which the recording of the output dot has been determined is given to other pixels adjacent to the pixel. The gist thereof is to include an influence storage means C1 for storing influences, and an increase/decrease correction means C2 for increasing or decreasing the threshold value determined for the other pixel according to the information stored in the influence storage means C1.

(Function) According to the halftone image recording device of the present invention, when the state of an output dot is determined for an arbitrary pixel, the influence that the determined output dot has on other pixels is stored in the influence storage means C1. Ru. Then, according to the information stored in the influence storage means C1, the increase/decrease correction means C2 increases or decreases the threshold values set for other affected pixels. Therefore, the threshold values of the other affected pixels are corrected to a threshold value corresponding to the practically expressible recording area, and the output dot signal is determined by the corrected value. 4 (Example) Hereinafter, in order to explain the present invention more specifically, an example will be given and explained.

FIG. 2 is a schematic perspective view of a halftone image recording device according to an embodiment, and is of the type that forms a latent image on a photoreceptor drum using laser light and develops this on recording paper to form an image. . Its configuration is generally the same as that of a well-known laser printer, and a charger 4 and a transfer device 6 are provided on the circumferential surface of the photoreceptor drum 2.
The photosensitive drum 2 is equipped with a cleaner (not shown), etc., and develops an optical latent image drawn on the photosensitive drum 2 by laser light during one rotation of the drum, as will be described later. Laser light is emitted from the semiconductor laser emitting element 8 toward the polygon mirror 10 . The polygon mirror 10 is a regular octagonal polygon mirror that is rotated at a stable speed, so that the laser beam is scanned at a constant speed in the horizontal direction as shown in the figure. The horizontally scanned light enters the synchronization mirror 14 and the rectangular reflection mirror 16 provided opposite the side wall of the photosensitive drum 2 through the fθ lens 12, and is reflected by the synchronization mirror 14. The laser beam reflected by the reflecting mirror 16 irradiates the photosensitive drum 2.

On the other hand, while the portion of the photosensitive drum 2 exposed by the laser beam reaches the transfer device 6 by rotation of the drum 2 in the direction of the arrow, the recording paper 20 is transferred to a well-known paper feeding roller 22.
．． 24 or the like, and is brought into close contact with the photosensitive drum 2. As a result, the latent image on the photoreceptor drum 2 is transferred to the recording paper 2.
0 to achieve recording of image gradation information.

In order for each device to operate in synchronization as described above,
Each device is centrally managed by an electronic control device 40.

That is, the electronic control I device 40 controls the laser emission of the semiconductor laser emitting element 8, the photosensitive drum 2, and the polygon mirror 10.
The image iR? input from the image reading section 50 that reads the rotation speed of the original image as a gray scale image. ? Control is performed based on the ft information, the detection result of the optical sensor 18, and the like. The control operation is performed by the cPU4 in the electronic control alli device 4 eZ.
0A is executed by operating according to a predetermined procedure (program) stored in the ROM 40B and information stored in the threshold table. Note that the RAM 40C is for temporary storage of information, and the RAM 40C is for temporary storage of information.
enables connection with external devices such as the image reading section 50.

The halftone image recording device configured as described above can precisely output fine, approximately circular dots (output dots) by irradiation with laser light, similar to known laser recording devices. Recording output can be performed over the entire surface of the recording paper 20. That is, as shown in FIG. 3A, the recording area of each output dot is controlled to be close to each other so that it partially overlaps with the recording area of other adjacent output dots. Note that the minimum area (pixel) for which the image reading device 50 detects shading
is set so that the recording area of the output dot covers (the fifth
(see figure).

Therefore, in the halftone image recording apparatus of this embodiment as well, an accurate linear relationship does not hold between the number of output dots and the recording area. 3(A) and (B) to D are explanatory diagrams visually showing the relationship between the state of output dots and the rate of increase in recording area in the halftone image recording apparatus of the embodiment.
). When recording output dots on arbitrary pixels, at least four output dots in the top, bottom, left and right, as typified by the pixel located at the center of FIG. G4. G5. Overlaps with G7.

However, in the halftone image recording device of the embodiment, when the output dots are sequentially recorded in the horizontal direction by scanning the laser beam (main scanning) and one line of scanning is completed, the rotation of the photosensitive drum 2 causes the laser beam to be irradiated. Scan the position vertically (sub-scan),
Finally, the recording of two-dimensional output dots is completed. Therefore, at the time of determining the output dot signal for the pixel of interest, the upper and left output drivers) rG2J, r
G4" status has been determined. Therefore, the actual increase in recording area when determining whether to turn on or off the output dot for the pixel of interest is sufficient if the three cases shown in FIGS. 3(B) to 3(D) are taken into consideration.

FIG. 3(B) shows two pixels G2. In G4, no output dots are recorded. At this time, the increase in the recording area when an output dot is recorded on the pixel of interest is the standard (1
00%), if the output dot is recorded on either the output driver G2 or 'G4 as shown in FIG.
% increase in recording area. Similarly, as shown in FIG. 3(D), when output dots are recorded in any pixel, approximately 36% of the area overlaps, and the increase in recording area is approximately 6%.
It remains at 4%.

The relationship between the output dots as described above holds true for all output dots, and if the output dots do not overlap each other, or if they occur at one location,
If it is possible to detect the occurrence of the problem in two places, the actual increase in recording area can be easily calculated. The relationship between the overlap of output dots and the increased recording area is stored in the ROM 40B in the electronic control unit 40.

In the halftone image recording device of the embodiment configured as described above, when the image gradation information of the original image is input manually from the image reading section 50, the image recording program stored in the ROM 40B is sequentially read out by the CPU 40A. When executed, a halftone image is recorded.

FIG. 4 shows a flowchart of the image recording program. The operation of the halftone image recording apparatus will be described below in accordance with the processing procedure of this image recording program.

First, when the processing of this program starts, the CPU4OA
The S
2). Next, the image gradation information H of one pixel to be processed this time is manually obtained from the image reading unit 50 (S4), and a comparison is performed between the threshold value S defined for that pixel and the image gradation information H (S6).

When the comparison result is Has, a process (S8) is executed to record an output dot for that pixel. That is, when the laser beam scans the position corresponding to the pixel, the modulation signal for the semiconductor laser emitting element 8 is created so that the laser beam irradiation is executed. On the other hand, when the comparison result is H≦S, a process (S10) in which recording of output dots is not executed is executed, and a laser modulation signal is created in which no laser beam is emitted.

In this way, when the processing of one pixel is completed, a determination is made as to whether or not the processing has been completed for all images (agricultural method information) manually input from the image reading unit 50 (S12), and the processing of all information is performed. When it is determined that the image recording program has been completed, the execution of the image recording program is terminated.

If the processing of all the image gradation information has not yet been completed, the recording status of the output dots corresponding to the alternatively executed processing S8 or S10 is stored (S14).
). In other words, the recording of output dots for a certain pixel is
Not only the recording of that pixel but also other pixels adjacent to that pixel are affected by the recording portion that protrudes.

Therefore, remember this influence. This corresponds to the recording state of output dots for pixel G2 for the pixel of interest shown in FIG.

Next, it is determined whether the currently processed pixel is the last pixel of one line (916). As shown in FIG. 3, there is no need to consider the recording state of the output dot for the last pixel of one line because there are no pixels further to the right. Therefore, the output dot recording state is stored only when it is determined that it is not the end of one line (C818), and when it is the end of one line, the process immediately moves to the next threshold value correction process (S20). That is, the storage of the output dot recording state in process 91B corresponds to the presence or absence of the arrangement of the output dot of pixel G4 with respect to the pixel of interest in FIG.

In this way, in the threshold value correction process (920) executed after the storage of the recording state of the output dots is completed, the threshold value is corrected as follows.

As for other pixels adjacent to the pixel where output dots are recorded, the recording area decreases by about 18% as shown in FIGS. 3(C) and 3(D). That is, in determining the threshold value S, the recording area is 10 by recording the output dots.
This means that the assumption of a 0% increase has collapsed. Therefore, the threshold value S is corrected to correspond to the area that actually increases when output dots are recorded in pixels whose recording area has decreased. For example, as shown in FIG. 3(C), when the protruding recording area of one output dot affects the pixel of interest, the threshold value S set for the pixel of interest is corrected by decreasing by 18%, and rO,82SJ shall be. Similarly, Fig. 3(D)
In the relationship shown in , a 36% reduction is corrected and the threshold S is set to rO
,64SJ.

In this way, after the successive correction of the threshold value to an appropriate value is completed, the image gradation information that continues from the image reading section 50 is manually read.
4), comparison with the threshold value corrected to the appropriate value (S6), etc.
Processing similar to the above is repeatedly performed on all image gradation information, and laser modulation signals are sequentially created.

After that, the semiconductor laser emitting element 8 is controlled based on the laser modulation signal, similar to the control of a normal laser printer.
is driven, and in synchronization with the driving, the rotation of the polygon mirror 16 and the photosensitive drum 2 is controlled, and an image is output onto the recording paper 20.

According to the halftone image recording apparatus of this embodiment configured as described above, the following effects are obvious.

The output dot signal is determined by a simple process of comparing the image density information with a threshold value.

Therefore, the electronic control device 40 can sufficiently cope with even a simple control system, and can perform high-speed image processing.

Further, the recording state of the output dots is sequentially stored, and information on the recording area that actually increases due to recording of the output dots for the pixel of interest can be accurately calculated. Based on this information, the threshold value for determining the output dot signal is changed to an appropriate value. Therefore, the density of the image reproduced by the halftone image recording device of this embodiment matches the density of the original image with high precision, and even on the high density side, it is possible to faithfully record the halftone original image with sufficient tonality. can.

Note that in the above embodiment, the processing of the halftone image recording device that adopts the simplest binary dither method has been described;
The present invention may be implemented in various ways without departing from the gist of the present invention, such as being applied to a halftone image recording device that employs a multi-value dither method in which a plurality of threshold values are set for one pixel.

Effects of the Invention As described above in detail with reference to embodiments, the halftone image recording device of the present invention stores the influence that the recording state of an output dot has on other pixels, and determines the influence based on that information. This is to correct the pixel threshold value to an appropriate value.

Therefore, a simple control system enables high-speed processing,
Moreover, the reproduced image faithfully expresses the halftones of the original image, and even at the high density side, it is possible to faithfully record the original image with sufficient gradation.

[Brief explanation of the drawing]

FIG. 1 is a diagram illustrating the basic configuration of the present invention, FIG. 2 is a schematic diagram illustrating the configuration of a halftone image recording apparatus according to an embodiment, and FIGS. FIG. 4 is a flowchart of an image recording program executed in the same embodiment, and FIG. 5 is an explanatory diagram of the overlapping area of output dots. C1...Influence storage means C2...Increase/decrease correction means 2...Photosensitive drum 8...Semiconductor laser emitting element 40...Electronic control unit 50...Image reading department agent Patent attorney Tsutomu Sadatsu (et al.) 2 people) Figure 1 Figure 4 Figure 5

Claims (1)

[Claims] 1. Halftone image recording that compares a threshold value defined for each pixel with the density of the original image of that pixel, determines the output dot signal of that pixel according to the comparison result, and records an image. In the apparatus, an influence storage means for storing an influence that a state of an output dot of the pixel has on an output state of another pixel adjacent to the pixel; A halftone image recording device comprising: an increase/decrease correction means for increasing/decreasing a predetermined threshold value.