JPH02164560A - Image forming device - Google Patents

Abstract

PURPOSE:To reproduce a picture element comprising low and high density sections under a good condition by correcting the condition of a bit information group for determining the strength of beam based on a bit information group for determining the irradiating time of beam. CONSTITUTION:Multi-level digital image information 1 is fed from a host through a page memory 3 to a line buffer 5 and subjected to D-D conversion through a look-up table, i.e. a RAM 6, then upper 4 bits of corrected 8 bit data are fed to a D/A converter 7 for PWM conversion and the lower 4 bits are fed to a laser beam amount modulating section 11. A laser driver 12 turns a laser diode 13 ON/OFF based on the pulse width information of higher 4 bits while the amount of light is controlled based on the density information of lower 4 bits when the laser diode 13 is turned ON. By such arrangement, a good multi-tone image is obtained and an image comprising low and high density sections can be reproduced under good condition.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an image forming apparatus, and more particularly to an image forming apparatus that inputs multivalued image data and forms a visible image including halftones.

[Prior Art] Conventionally, when outputting a halftone image using a laser beam printer using electrophotographic technology, a computer, a controller, etc., which is a data source, performs halftone dot processing, dither processing, etc.
The method used was to perform image processing such as PWM, convert it into a binary value, and then input it to the printer.

[Problems to be Solved by the Invention] This method handles binary signals, so it is possible to transfer halftone data with high efficiency by compressing the transfer data, etc., but on the other hand,
Regarding the density in the depth direction, due to delays in the data transmission path, electrophotographic process conditions, variations between devices, etc., it is difficult to obtain the desired stable gradation even though the same halftone image data is sent from the host computer or controller. It was difficult to obtain.

In addition, when using different printer models using the same host computer or controller, the correspondence between dither patterns and density differs depending on the printer, so the density correction table depending on the printer must be connected to the number of printers. A situation exists in which printers require only a host computer or controller, making it difficult to maintain compatibility between printers.

As image data having gradations, for example, there is a method in which a document is read with an image reader, developed into a dot image, and a value in the depth direction is given to each dot. Figure 3 (a
) and (b) are diagrams showing the input/output characteristics of the CCD. When using, for example, this CDD sensor as the image input section of Image League, the density information of the original image is converted into voltage information in the sensor section that is approximately linear with the reflected light from the original image, as shown in Figure 3 (a). is converted to This voltage information has a logarithmic relationship with the concentration (Figure 3 (b)).
, this signal is corrected (γ correction) in the reader section. However, the image changes greatly depending on the degree of correction.

Additionally, the connected host computers have different fonts from different companies, depending on the model, and some tend to make the characters thicker, while others tend to make the characters look thinner and neater.

Since there are many variables involved in reproducing image information, conventionally, when a single system was constructed using a league, a host computer, a printer, etc., the resulting image was generally blurry or the text was thin. On the other hand, there were some inconveniences, such as the overall appearance of the text being dark and the letters being crushed. In severe cases, the letters may be thin, but the photographs and graphics are flattened and have no gradation, or conversely, the letters are thick and flattened, but the photographs and graphics are blurred.

As a method to solve this problem, pulse width modulation (PW
The applicant of the present application has proposed a method in which the exposure time per dot of the exposure beam is controlled and the density is modulated isometrically by M). Furthermore, attempts have been made to overcome the various problems described above by making the density modulation steps finer in order to perform faithful density modulation. however,
In order to finely perform the density modulation steps, the processing amount of the pulse width modulation section (particularly the D/A converter, etc. therein) increases significantly7, which causes problems such as increased complexity of the circuit and decreased processing time. Was.

The present invention has been made in view of the related art, and aims to provide an image forming apparatus that simplifies the burden on the processing system that determines the beam irradiation time and that makes it possible to obtain good halftone images. It is something.

[Means for Solving the Problem] An image forming apparatus of the present invention that solves this problem has the configuration shown below.

That is, in an image forming apparatus that generates a beam of light based on input data and forms a visible image by irradiating the beam of light onto a photoreceptor, an input means for inputting multivalued pixel data expressed in N bits; a first control means for controlling the irradiation time of the beam light based on the state of a predetermined bit group of the multi-value pixel data; , a second control means for controlling the emission intensity of the beam light, and the first and second control means for controlling the emission intensity of the beam light.
and irradiation means for irradiating the photoreceptor with a beam of light controlled by the control means.

[Operation] In the configuration of the present invention, when N input by the input means
Multilevel pixel data consisting of bits is input. Then, the first control means controls the irradiation time of the beam light according to the state of a predetermined bit group of the pixel data.
Based on the state of the bit group excluding the predetermined bit group,
The second control means controls the emission intensity of the beam light. The irradiation means irradiates the photoreceptor with the beam light having the determined beam light irradiation time and emission intensity.

[Embodiments] Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

<Description of the first embodiment (Figs. 1 to 6)> In Fig. 1,
A block configuration diagram of a printer device in this embodiment is shown, and an outline of its processing will be explained below.

Multivalued digital image data 1 (8 bits per pixel = 256 gradations) output from a data source (not shown) (host computer YΔ image reader, etc.) is stored in the page memory 3 in the printer through the I10 port 2. Ru. The pixel data arranged as 8-bit multi-level video data in the page memory 3 is sequentially read out to the line buffer 5 at the start of printing, and synchronized with the video signal.
Digital-to-digital conversion is performed at M6.

FIG. 2 shows an example of the contents of the lookup table in the RAM 5. Note that the lookup table inputs input data to the address line of the RAM 6 and outputs the data written at that address from the data line.

For example, in FIG. 2, when AOH is input as image density data, data converted to 90H is output.

By the way, in FIG. 1, 26 is a selector,
The CPU 10 selects the ROM 4 according to the state of this selector.
One of the lookup table information stored in advance is read out and the data is loaded into the RAM 6. Each curve information shown in FIG. 4(a)(b) is stored in this ROM.
4, however, more curve information may be stored to make it more detailed.

The characteristics shown in Fig. 4(a) mainly take into account only the output characteristics of the printer, and the curves I, TI
If you select , the output image will be darker, and if you select IV or V, you can make the output image lighter. The characteristics shown in FIG. 4(b) are obtained by logarithmically correcting the characteristics shown in FIG. 4(a), taking into account both the output characteristics of the printer and the COD input characteristics of the league. Also in FIG. 4(b), curves I and II darken the output image with respect to the characteristics of curve m, and +
V and V adjust the output image to make it lighter.

In any case, the 8-bit gradation data corrected in the RAM 6 is then converted to 0 to 256 by the D/A converter 7.
level is converted to an analog signal.

This analog signal is sent to a signal generator 8 by a comparator 9.
The signal is compared with a triangular wave of a predetermined period outputted from the sensor, and is subjected to conversion from a depth direction signal to a length direction signal, that is, pulse width modulation.

This situation will be explained with reference to FIG.

Signal A in FIG. 5 is an image signal output from D/A converter 7, and signal B is a triangular wave from signal generator 8. These signals A and B are synchronized by a video clock as shown.

Now, the signals A and B are compared by the comparator 9, and a signal C having a length corresponding to the level of the signal A is generated (when the signal A<B, the output of the comparator 9 is O
). Note that the signal from the signal generator 8 may be a repetitive signal with a predetermined period, and does not necessarily have to be a triangular wave.

The output signal of the comparator 9 (signal after pulse width modulation) is input to the laser driver 12, and the laser diode 13
to drive. The laser light generated from the laser diode 13 is swung left and right by a polygon mirror 14 rotating at a constant speed to scan the photoreceptor 19. At this time,
A portion of the scanning light is received by a beam detector (not shown) and used as a video signal or a synchronizing signal for the signal generator 8.

The photoreceptor 9 is uniformly charged by a charger 17 and then subjected to the laser scanning described above to form an electrostatic latent image on its surface. This latent image is then developed using a developing device 18. This developed pattern is transferred onto the transfer material 23 by the transfer charger 2Q and fixed by the heat fixing roller 24□25. Photoreceptor 19
The developer remaining without being transferred to the surface of the photoreceptor is collected by a cleaner 21, and the charge on the photoreceptor is erased by pre-exposure 22, and the same process is repeated again.

Although an image output including halftones is obtained in the above manner, the laser light amount modulation unit 11 proposed by the present invention will be explained below.

FIG. 6(a) shows the output light of 8-bit data corrected by the RAM 6, and FIG. 6(b) shows how dots are generated for one pixel of an image obtained by laser New Year's modulation.

As shown in the figure, the 8-bit data corrected and converted from RAM6 is used for PWM conversion (D/A converter 7).
), and the lower 4 bits are output to the laser beam m modulator 11.

Then, the L maser driver 12 turns on/off for a predetermined time according to the pulse width information expressed by the upper 4 bits, and controls the amount of laser power based on the density information based on the data of the lower 4 bits.

Now, the corrected data from RAM6 is shown in Figure 6 (a
), it is assumed that the value is 87H (H indicates a hexadecimal number).

The printer must express the density of "87H (135 in decimal notation)", that is, 135/256, for a pure black with a density of "FFH (255 in decimal notation)".

Therefore, the upper 4 bits are °'80H (density: 12
8/256=172)”, that is, “FFH” Xi/
In addition to controlling the laser emission time by obtaining a PWM output that generates a pulse width of 2,
” by changing the intensity of the laser light amount, “’ 1.28/256+7/256=135/256
°.

This is what we tried to achieve.

Here, it will be explained that density expression is achieved by laser light intensity modulation.

(b-1) in FIG. 6(b) shows the signal waveform after pulse width modulation. The waveform shown in (b-2) is the pulse width (determined by PWM modulation) based on (b-1), and the dot diameter is determined by the threshold value for creating a latent image on the drum when the laser light intensity is changed and the laser output is increased. becomes larger (dashed line), and as a result, as shown by the broken line in (b-3), the area of the latent image is modulated, that is, the density per dot is modulated.

Therefore, as shown in FIG. 6(C), the current source 50 that flows through the laser diode is connected to I, IX2. By giving weights such as IX4 and IX8 and controlling the drive current of the laser diode 13 by laser light intensity modulation input, the input multi-level image is roughly expressed using a PWM circuit, and then the density interpolation is performed by modulating the laser light intensity. . As a result, it has become possible to perform 256 multiple gradations that can be expressed with 8 bits by dividing the processing of each 4 bits of PWM modulation and light intensity modulation, allowing multiple gradations to be performed efficiently with a simple configuration and in a short processing time. You will be able to get it.

<Description of other embodiments (Figs. 7 to 10)> In the first embodiment described above, the lower 4 bits are directly input to the laser light amount modulation section as laser light amount modulation data, and the upper 4 bits D We have explained the case where the weight of 1 bit of /A input is divided into 16 equal parts by this laser light intensity modulation, the laser power is corrected to the level according to the input data value, and the density gradation value is optimized. The laser power and the area of increase in the dot diameter of the latent image are not in -order proportionality. Also, PW
Regarding the pulse width obtained by the M modulation output, the density change corresponding to one bit with respect to the PWM value at that time may not be constant between high density and low density mainly due to electrophotographic characteristics.

FIG. 7 shows an embodiment that can further solve this problem. As shown in the figure, the lower 4 bit data is corrected using a table (memory) 28 that corrects it according to the input of the upper 4 bits. Accordingly, the weight of one bit of the digital value obtained by the P'vVM circuit can be related to the next increasing value in a linear manner.

The correction table 28 selects a 16 fmB conversion table based on the PWM modulation input 4-bit data shown in FIG. 6(a). This conversion table stores the most suitable correction data for performing laser light intensity modulation in each density rank, and the light intensity correction using the 4-bit laser light intensity modulation input data shown in Fig. 6(a) is stored. This will allow you to make the best corrections.

In the example explained above, the 8-bit multi-value data was divided into the upper 4 bits and the lower 4 bits, but of course there is no need to specify the number of bits for the multi-value data, and the data division Regarding the method, for example, even when the lowest 1 bit shown in Fig. 8 is operated as a laser light intensity switching signal, the burden of PWM (resolution) is lower than that of the conventional method which uses PWM modulation. is halved, which sufficiently exhibits a large effect for the purpose of the present invention.

Furthermore, as shown in Figure 9, bits can be divided alternately,
As shown in Fig. 10, one bit of the multilevel density data is positioned as a sign bit indicating whether or not to perform laser light intensity modulation. P divided by light intensity modulation
It is also possible to perform gradation expression using only WM, and if the sign bit is ON, perform PV/M+laser light intensity modulation and freely switch the number of gradations using the data format.

Naturally, as the number of gradations of multi-value data increases, the number of bits of multi-value data also increases, but in any case, the share of concentration expression between PWM and laser light intensity modulation of the data bit number N is as follows:
2N methods are possible. Here, as a typical example, only the case where PWM/laser sight are each 4 bits is shown. In addition, although PWM was explained in the above example, it is obvious that other halftone processing techniques such as dither and error diffusion can achieve the same effect when used in combination with the light intensity modulation of this proposal, so the explanation is omitted. do.

As explained above, according to this embodiment, by controlling the beam light intensity based on multivalue input pixel data, it is possible to reduce the burden on the circuit system that controls the beam light irradiation time, and furthermore, , it becomes possible to reproduce a good multi-tone image with a simple configuration.

In addition, by correcting the state of the bit information group that determines the beam light intensity based on the bit information group that determines the beam light irradiation time, pixels in low density areas and high density areas can be reproduced in good condition. becomes possible.

[Effects of the Invention] As explained above, according to the present invention, by controlling the beam light intensity based on multi-level input pixel data, the load on the circuit system that controls the beam light irradiation time is reduced, and therefore With this configuration, it is possible to reproduce a good multi-tone image.

In addition, by correcting the state of the bit information group that determines the beam light intensity based on the bit information group that determines the beam light irradiation time, pixels in low density areas and high density areas can be reproduced in good condition. becomes possible.

[Brief explanation of the drawing]

Fig. 1 is a block diagram of the laser beam printer in this embodiment, Fig. 2 is a diagram showing the conversion characteristics of the lookup table in this embodiment, and Fig. 3(a) shows the relationship between the output voltage of the CCD and the original reflection light aperture. Figure 3 (b) is a diagram showing the relationship between CCD output voltage and original density; Figure 4 (a) and (b) are diagrams showing the characteristics of a group of lookup tables prepared in advance. Figure 5 is a diagram showing the principle of pulse width modulation, Figure 6 (a) is a diagram showing the usage of each bit that makes up the pixel data after correction, and Figure 6 (b) is a diagram showing the use of each bit that makes up the pixel data after correction. FIG. 6(c) is a diagram showing a specific example of light intensity modulation; FIG. 7 is a block configuration diagram of a laser beam printer in another embodiment; FIG. 8 ~FIG. 10 is a diagram showing an application example of the usage of each bit constituting the corrected pixel data in another embodiment. In the figure, 2... I10 boat, 3... page memory,
4...Selector, 5...Line buffer, 6...
RAM, 7...D/A converter, 8...signal generator,
9... Comparator, 10... CPU,... Laser light amount modulation section, 12... Laser driver, 3... Laser diode, 19... Photoreceptor. Canon Co., Ltd. 0H AOH FH Input data 2nd diagram Den g Tomobu striped anti 4"l Likelihood Hara Go:, R, 屓 (b) Figure 3 → YoF 'f To also PWM ff1T! 1 person h Lehr Input ``-likelihood'' (O) (b) Figure 6 Figure 8 Figure 9 Figure 10

Claims (2)

[Claims] (1) In an image forming apparatus that generates a beam of light based on input data and forms a visible image by irradiating the beam of light onto a photoreceptor, an input means for inputting multivalued pixel data expressed in N bits; , Based on the state of a predetermined bit group of the multivalued pixel data,
a first control means for controlling the irradiation time of the beam light; and a second control means for controlling the emission intensity of the beam light based on the states of bit groups other than the predetermined bit group of the multivalued pixel data. and irradiation means for irradiating the photoreceptor with beam light controlled by the first and second control means. (2) Claim 1, further comprising a correction means for correcting the state of a bit group that is a control source of the second control means based on a predetermined bit group that is a control source of the first control means. The image forming apparatus described in .