JPS63157558A - Image recorder - Google Patents

Abstract

PURPOSE:To perform an image recording using the resolution of recording device at its maximum by recording an image by modulating it by a different density pattern according to whether it is a binary picture or a multilevel picture or an image impossible to be decided. CONSTITUTION:An image reader 2 reads the image on an original including a halftone, and converts it into the multilevel image digital signal and outputs it. This signal is transmitted to a frame memory 3, and is store by one page portion of the original. The output of the frame memory 3 is supplied to a multilevel density pattern generation circuit 6 through a meaning circuit 4 and a line memory 5, and a multilevel picture recording signal is generated. On the other hand, the output of the frame memory 3 is transmitted to a dither/binarization circuit 8, and the signal, which is processed by a dither processing or by a binarization processing, is supplied to a multilevel-binary- dither switching circuit 11. The switching circuit 11 is switched and selected by the decision output of an image classification decision circuit 10, and the selected signal is transmitted to a thermal head driving circuit 13.

Description

[Detailed Description of the Invention] [Objective of the Invention] (Industrial Application Field) The present invention relates to an apparatus for recording images by a thermal transfer recording method, etc., and in particular, it relates to a device for recording images using a thermal transfer recording method, etc. The present invention relates to an image recording device that performs expression.

(Prior art) The thermal transfer recording method presses a thermal spatula onto a recording paper via an ink film using heat-melting or heat-sublimating ink, and uses the heat generated when the heating resistor of the thermal head is energized. This method transfers ink on an ink film to recording paper.

The thermal transfer recording method using hot-melt ink is originally a method suitable for recording binary images with density levels of only rlJ and rOJ, but when recording multi-valued images, that is, images with gradation, Requires special concentration modulation techniques.

As a density modulation technique, pseudo halftone recording has heretofore been attempted in which a halftone image is expressed by dot density or ink occupancy within a certain area.

This is a method widely used to express gradation on dot printers, which only have the ability to express binary density.
Typical examples include the dither method and the density pattern method.

The dither method is a method of binarizing a multilevel image using a threshold pattern as shown in Figure 7, and the density pattern method has a one-to-one correspondence with the gradation level as shown in Figure 8. This is a method of recording a multivalued image using a pattern (fixed pattern).

Additionally, the present inventors have proposed a multilevel density pattern method, which is a further development of the density pattern method (Japanese Patent Application No. 1983).
0-18768). With the dither method and the normal density pattern method, it is difficult to satisfy both the number of gradation levels and the resolution necessary to obtain a comparable image in consideration of human visual characteristics. In addition, due to the heat storage effect in the thermal head,
Particularly in medium and high density areas, there are problems such as gradation discontinuity, such as crushing areas that should be whitened out, and unstable ink adhesion in low and medium density areas, resulting in noticeable roughness of the image. . According to the multilevel density pattern method described above by the present inventors, by actively utilizing the heat storage effect of the thermal head, which has been considered an obstacle to good recording in the past, graininess can be achieved with stable gradations. This makes it possible to record high-quality images with less noise.

For example, as shown in FIG. 9, this multilevel density pattern method
One pixel is composed of a matrix of multiple dots such as 3 x 3, and the density level range of the multilevel image signal is divided into multiple partial density regions, such as low density region, medium density region, and high density region. However, three fixed patterns A to C are used corresponding to each of these portions and the a degree area.

The fixed patterns A to C are multivalued patterns in which the recording energy applied to the dots constituting them can be modulated in accordance with the density level of the multivalued image signal (see FIG. 10).

Specifically, for example, fixed pattern A for low density is an isolated dot pattern formed by isolating one dot in one pixel, and the gradation of the low density area is determined by recording energy (energy injected into the thermal head). It is expressed by modulating and changing the size of the dots. Fixed pattern B for medium density is a striped pattern extending in the relative movement direction (sub-scanning direction) between the thermal head and the recording paper, and the gradation in the medium density area is determined by the thickness of the stripe by the injection energy of the thermal head. It is expressed by changing. Furthermore, the fixed pattern C for high density is an L-shaped pattern with a white part for 2 x 2 dots, and the area of the white part can be changed by the injection energy of the thermal head for high density gradation. is expressed by If halftone recording is performed using such a multi-level density pattern method, the problems that occur with the dither method or the normal density pattern method can be solved.

However, the above-mentioned multi-value density pattern method or normal density pattern method is designed for recording multi-value images, and when handling binary images, one pixel of image data is N
The data is enlarged to a matrix size of XN and recorded. For this reason, when an image containing a mixture of multilevel and binary images is recorded using these methods, the resolution of the recording means, such as a thermal head, cannot be fully utilized in the binary image portion, and the recorded image is The resolution will decrease.

(Problems to be solved by the invention) In this way, in the density pattern method and the multivalued density pattern method,
When recording a binary image, there is a problem in that the resolution is lower than in a normal binary image recording method.

Therefore, when recording an image containing a mixture of multivalued images and binary images, the present invention is capable of recording a binary image that makes maximum use of the resolution of the recording means without degrading the image quality of the multivalued image. The purpose is to provide a recording device.

[Structure of the Invention] (Means for Solving Problems) The present invention provides means for determining whether an original image is a multivalued image or a binary image, and when it is determined that the original image is a multivalued image, a density pattern method or a multivalued image is used. Recording is performed using a multivalued image recording signal generated using at least the value density pattern method, that is, an operation of selecting a fixed pattern formed in a matrix of dots bx of an order expressing one pixel according to the original image signal. Let's do it.

On the other hand, when the original image is determined to be a binary image, the recording energy given to each dot of the multivalued image recording signal generated as described above is determined by binarizing the original image signal. Recording is performed by individually modulating the binary image signal.

Furthermore, when it is impossible to determine whether the original image is a multivalued image or a binary image, the recording energy given to each dot of the multivalued image recording signal is determined by a dithered image signal obtained by modulating the original image signal with a dither pattern. Recording is performed by individually modulating the

(Operation) When the original image is determined to be a binary image, the dot for recording the binary image is selected from among the series of multi-value image recording signals obtained by selecting a fixed pattern according to the original image signal. The density level of the dot, that is, the recording energy applied to the dot, is modulated according to the binary image signal. Therefore,
While the multi-value density pattern method or the density pattern method is used to record multi-value images, the high-density pattern method that utilizes the maximum resolution of recording means such as thermal heads for binary images is used in the same way as normal binary image recording. Quality records are made.

In addition, it is not always possible to clearly determine whether the original image is a multilevel image or a binary image, so if the distinction between the two is ambiguous, it is determined that it is impossible to distinguish between the two, and dither recording is performed to prevent deterioration of image quality. . The dithered image obtained in this case also takes full advantage of the resolution of the recording means, similar to the binary image.

(Embodiment) FIG. 1 shows an outline of an embodiment in which the present invention is applied to an image recording apparatus that records a multi-value image by a multi-value density pattern method.

In FIG. 1, the CPUI is used to control the entire apparatus, and controls the image reading device 2, recording control circuit 15, and timing circuit 16.

The image reading device 2 is a device that obtains an image signal by reading an image (original image) on a document containing halftones, and converts the image signal into a multi-valued digital signal (expressed by 8 bits per pixel, for example). Output. The frame memory 3 is an image memory for storing image signals for one page of a document read by the image reading device 2, and is unnecessary if the image reading operation and the recording output operation are not temporally separated. .

The output of the frame memory 3 is input via the averaging circuit 4 and the line memory 5 to a multi-value density pattern generation circuit 6, and a multi-value image recording signal is generated.

That is, the averaging circuit 4 is a circuit that performs averaging processing of MXN corresponding to the matrix size MxN dots of the multilevel density pattern on the multivalued image signal data from the frame memory 5, and this averaged data is The data is transferred to the memory 5 one line at a time (8542 minutes before averaging). The multi-value density pattern generation circuit 6 uses this one line of data to generate a multi-value image recording signal of a multi-value density pattern consisting of a matrix of MXN dots.

This multi-value image recording signal is sent to the multi-value density pattern generation circuit 6.
The spatial size of the input multivalued image signal is expanded by M times in the main scanning direction and by N times (N lines) in the sub-scanning direction. Therefore, the line memory 5 is supplied with the averaged multi-value image signal for one line every N lines of the multi-value image recording signal from the averaging circuit 4. Multilevel density pattern generation circuit 6 is controlled by matrix address generation circuit 7.

The dither/binarization circuit 8 is a circuit that performs dither processing and binarization processing on the image signal output from the frame memory 3 to generate a dither image signal and a binary image signal. As shown in the figure.

In FIG. 3, multivalued image signal data read from the frame memory 3 of FIG. 1 is input to a dither matrix table ROM 31 and a comparator 33.

The ROM 31 is controlled by a matrix position setting counter 32, modulates manually input image signal data with a dither pattern consisting of an mxn matrix, and outputs the dither image signal as a 1-bit data string. In addition,
The matrix size mxn for this dithering may be the same as the matrix size MXN of the multilevel density pattern.

On the other hand, the comparator 33 binarizes the image signal data from the frame memory 3 using a threshold value (binarization level) determined by the binarization level setting circuit 34, and generates a binary image signal also consisting of a 1-bit data string. Output. Note that it is also possible to perform the binarization process without fixing the binarization level and changing it depending on the input image signal.

Returning to FIG. 1, the output of the frame memory 3 is further input to an image type determination circuit 10 via a filter circuit 9. FIG. 4 shows the detailed structure of the filter circuit 9 and the image type determination circuit 10, and shows the structure of the frame memory 3.
The multivalued image signal data from is first added for a total of 9 pixels, 3 pixels in the main scanning direction and 3 pixels in the sub-scanning direction. That is, the line delay circuit 4 is connected via the line switching circuit 41.
2a and 42b hold multi-value image signal data for two lines, these are added by an adder 43a, and this addition result and the multi-value image data of the current line (output of the delay circuit 44a) are added. Added by adder 43b. The result of this addition is the delay circuit 44c~
44e, the outputs of each of these delay circuits 44c to 44e are sequentially delayed by one pixel at a time, and the outputs of these delay circuits 44c to 44e are sent to adders 43c and 44e.
By performing the addition in 3d, an addition result for 9 pixels is obtained.

The result of addition for nine pixels is reduced to 1/9 by the ROM 45 in order to obtain an average value for each pixel, and further converted into a complement. Since the high-frequency component of the original image signal is used to determine the type of image, averaged image signal data (ROM
45 output) and the original image signal data (delay circuit 44 output) and the original image signal data (delay circuit 44 output)
The high-frequency component is extracted by adding the output of the output signal b) with the adder 43e. Note that the delay circuits 44 a, 44
b is for determining the temporal timing of both data when performing this addition.

The high-frequency component of the average value of the nine pixels obtained by the filter circuit 9 is input to the image type determination circuit 10, and is first binarized by the binarization circuit 46, and then by the line switching circuit 47.
The signals are sequentially delayed one line at a time by line delay circuits 48a to 48c. Line delay circuit 481~
The data of 9 pixels in total, 3 pixels each of the output of 48c, is judged R.
The OM 49 is manually operated to determine whether the image is a multivalued or binary image.

The determination ROM 49 determines whether the input image is a multivalued image or a binary image, but depending on the image, the determination may not be made clearly and the input image may be determined to be an intermediate image between the two. Therefore, in the case of an intermediate image, a determination result of an undetermined undetermined image is output. In addition, the judgment ROM 49 also receives a recording mode setting signal, which is a control signal from the CPUI, and can change the judgment level or forcibly judge a multi-valued image or a binary image, etc., regardless of the type of image. It is now possible to output the results. Note that as a specific method for determining such image type, the technique described in Japanese Patent Application Laid-open No. 82577/1982, which is a patent application filed by the present applicant, can be used.

The multivalue/binary/dither switching circuit 11 is the image type determination circuit 1
This circuit switches the recording image mode based on the determination result of 0, and when the determination result of the determination circuit 10 is a multi-value image, the multi-value image recording signal from the multi-value density pattern generation circuit 6 is output as is.

If the determination result is a binary image, the recording energy given to each dot of the multi-value image recording signal is individually modulated by the binary image signal from the dither/binarization circuit 8. and then output.

In addition, if the judgment result is indeterminate (impossible to judge), the recording energy given to each dot is individually modulated using the dither image signal from the dither/binarization circuit 8, and then outputted. do.

The multivalue/binary/dither switching circuit 11 performs the switching for each recorded dot. Figure 2 shows this situation.
a) shows data of a multi-value image recording signal converted into a multi-value density pattern by the multi-value density pattern generation circuit 6, and (b)
) and (c) show data of a dither image and a binary image obtained by the dither/binarization circuit 8, respectively. Further, FIG. 2(d) is an example of the judgment output of the image type judgment circuit 10,
A indicates the determination result of a multi-valued image, B indicates the determination result of an indefinite (undeterminable) image, and C indicates the determination result of a binary image. The multi-value/binary/dither switching circuit 11 switches the recording output image according to this determination result, but this switching is performed depending on whether the recording output image is mainly a multi-value density image or a binary image. figure(
e) It can be changed as in (f).

In order to determine the recording density of the binary image and the dithered image, the binary/dithered image density generation circuit 12 generates a signal that specifies the recording energy (the energy injected into the thermal head) so that the recording dot becomes exactly the size of one dot. This is a circuit for generating .The symbol ``■'' on the pattern shown in FIG. 2 represents the recording energy corresponding to the recording density of the binary image.

The multi-value image recording signal outputted from the multi-value/binary/dither switching circuit 11 in this way is transferred to the thermal head drive circuit 13.
supplied to The thermal head drive circuit 12 is a circuit that converts a multi-value density pattern given by a multi-value image recording signal into a pulse width of a pulse that drives the thermal head in the thermal transfer recording device 14, and controls the energy injected into the thermal head. do. The recording control circuit 15 is a circuit that controls the thermal transfer recording device 14, and specifically
The ink ribbon, recording paper, etc. are transported and controlled by commands from the PUI. The timing circuit 16 generates a one-line synchronization signal necessary for transferring image signal data, a timing clock for data transfer, etc.
Supply to necessary circuits.

FIG. 5 is a timing chart showing the operation of this embodiment, and one cycle of the dot clock corresponds to the recording time of one dot in the thermal head. The multi-value image signal is switched once every four periods of the dot clock, and during this period, the multi-value density pattern generation circuit 6 is controlled by the matrix address generation circuit 7 to generate a four-dot multi-value image recording signal.

On the other hand, the binary image signal and dither image signal from the dither/binarization circuit 8 are input as data corresponding to one dot in the thermal head, and this binary image signal is applied to each dot of the multi-value image recording signal. Recording energy is modulated. In other words, the recording energy given to the dot where the binary image signal or dither image signal is "1" in the series of multilevel image recording signals is as shown in FIG. 2(e) or (f).
), and the recording signal output 1 or 2 shown in FIG. 5 is finally obtained.

In this way, a multi-value image using the multi-value density pattern method,
It is possible to record a binary image in which one pixel corresponds to one dot of the thermal head.

Note that the present invention is not limited to the above embodiments,
For example, it is also possible to replace the multi-value/binary/dither switching circuit 11 and the binary/dither image density generation circuit 12 in FIG. 1 with a ROM pattern table 60 as shown in FIG. be. X counter 61. Y counter 62 generates address data in the X direction and Y direction,
These, the multi-value image recording signal from the multi-value density pattern generation circuit 6, the binary image signal and dither image signal from the dither/binarization circuit 8, and the determination signal from the image type determination circuit 10 are stored in the ROM pattern table 60. is given as address input. Note that it is also possible to configure the ROM pattern table further including the multilevel density pattern generation circuit 6 and the image type determination circuit 10 shown in FIG.

Further, in the present invention, the binary image signal may be a signal obtained by performing processing such as edge detection or single thin line character detection on a multivalued image signal and converting it into a binary value.

Furthermore, in the embodiment described in "-", the multi-value image is recorded using the multi-value density pattern method explained using FIGS. 9 and 10, that is, the density level range of the multi-value image signal is divided into a plurality of partial density regions. , a method of selecting a fixed pattern according to which partial density region the multi-valued image signal exists, and modulating the recording energy given to the dots forming the selected fixed pattern according to the density level of the multi-valued image signal. However, it is also effective when using a normal density pattern method as shown in Figure 8, that is, a density pattern method that uses a pattern that corresponds one-to-one to the gradation level of a multivalued image as a fixed pattern. be.

In the case of this normal density pattern method, since the recording energy of each dot takes only binary values, the binary/dither image density generating circuit 12 shown in FIG. 1 is not necessary.

In addition, when recording an image from a color image reading means, a color image sensor (low resolution) is used as the image reading means.
A monochrome image sensor (high resolution) may be used to determine whether the image is a binary image or a multivalued image based on the image signal from the monochrome image sensor.

Further, the dither matrix for dithering may be a multi-value density pattern, in which case switching is performed in the multi-value/binary/dither switching circuit 11 for each dot, pixel, or larger unit. However, no unnaturalness occurs.

Furthermore, although the above embodiments have described thermal transfer recording, the present invention can also be applied to thermal recording methods using heat sublimation ink, wire tod type impact printers, and electrophotographic recording devices. be. In addition, the present invention may be modified and implemented in various ways without departing from the scope of the invention.

[Effects of the Invention] According to the present invention, in an image recording device that records one pixel by selecting a fixed pattern formed in a matrix represented by a number of rows of dots, when recording a binary image, one pixel is It is possible to correspond to one dot of the recording means, and it is possible to record a high-resolution binary image determined by the resolution of the recording means without deteriorating the image quality of the multi-valued image.

Furthermore, in the present invention, if it is impossible to determine whether the original image is a multivalued image or a binary image, recording as a dither pattern enables recording without deterioration of image quality.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing a schematic configuration of an image recording apparatus according to an embodiment of the present invention, and FIG. 2 is a block diagram showing a schematic configuration of an image recording apparatus according to an embodiment of the present invention. A diagram for explaining how to apply recording energy to each dot. Figures 3 and 4 are block diagrams showing the configuration of the main parts of Figure 1 in detail. Figure 5 shows the operation of the same embodiment. A time chart, FIG. 6 is a block diagram showing the configuration of main parts according to another embodiment of the present invention, and FIGS. 7 to 10 are diagrams for explaining a conventional multi-level image recording method. DESCRIPTION OF SYMBOLS 1...CPU, 2...Image reading device, 3...Frame memory, 4...Averaging circuit, 5...Line memory, 6...Multi-value density pattern generation circuit (multi-value image recording signal generation means), 7... matrix address generation circuit, 8... dither/binarization circuit, 9... filter circuit, 10... image type determination circuit (determination means),
12... Multi-value/binary/dither switching circuit, 13... Thermal head drive circuit, 14... Thermal transfer recording device, 1
5... Recording control circuit, 16... Timing circuit. Applicant's Representative Patent Attorney Takehiko Suzue Figure 1 Figure 2 Figure 3 - Figure 6 Figure 7 Figure 8 Figure 9 Figure 10

Claims (3)

[Claims] (1) Means for generating a multivalued image recording signal by configuring one pixel as a matrix of a plurality of dots and selecting a pattern formed within the matrix according to the original image signal, and the original image signal. binarization means for generating a binary image signal by binarizing the original image, a dithering means for generating a dithered image signal by modulating the original image signal with a dither pattern, and a dithering means for generating a dithered image signal by modulating the original image signal with a dither pattern; a determining means for determining whether the original image is an image; and when the determining means determines that the original image is a multivalued image, outputs the multivalued image recording signal; and when the original image is determined to be a binary image, it outputs the multivalued image recording signal; The recording energy applied to each dot of the multilevel image recording signal is modulated individually according to the binary image signal and outputted, and when determination is impossible, the recording energy applied to each dot of the multilevel image recording signal is An image recording apparatus comprising means for individually modulating and outputting a dithered image signal according to the dithered image signal, and means for recording an image using a multivalued image recording signal outputted by the means. (2) The means for generating the multilevel image recording signal divides the density level range of the original image signal into a plurality of partial density regions, and generates a fixed pattern depending on which partial density region the original image signal exists. 2. The image recording apparatus according to claim 1, wherein the image recording apparatus selects the fixed pattern and modulates the recording energy applied to the dots constituting the selected fixed pattern in accordance with the density level of the original image signal. (3) The image recording apparatus according to claim 1, wherein the means for generating the multi-valued image recording signal uses a pattern that corresponds one-to-one to the gradation level of the original image. .