JPH02252568A - Image forming apparatus - Google Patents

Abstract

PURPOSE:To obtain an image which is not black as a whole and has excellent gradation by providing converting means for converting multilevel pixel data into multilevel pixel data having low density value, and energizing means for energizing the converting means at each predetermined pixel period. CONSTITUTION:Since a digital image signal 116 has 4 bits, input data become a value of O-FH (H is hexadecimal number). The larger the value is, the nearer the data becomes white. A negative edge trigger flip-flop 123 outputs a video clock 111 divided by two as a VIDEO mask signal 124. The signal 116 is logically added with the signal 124 by OR gates 119-122, and input to a latch circuit 101 as a signal 117. Accordingly, the signal 117 becomes 'FH (white)' at its value at every other one.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an image forming apparatus, and more specifically, to an image forming apparatus, which performs pulse width modulation by comparing a pattern signal of a predetermined period with an image density signal, and performs pulse width modulation based on this pulse width modulation signal. The present invention relates to an image forming apparatus that forms a visible image.

[Prior Art] Conventionally, there are methods of reproducing halftone images by using a dither method or a density pattern method. However, in any case, using a small size threshold matrix
Sufficient gradation cannot be obtained. Therefore, it is possible to express gradation using a large-sized threshold matrix, but this has the problem of extremely low resolution. .

On the other hand, a method has been proposed that uses a relatively simple device configuration to express gradation while maintaining high resolution.

This method involves converting the input digital image signal (indicating the density value) into an analog signal in order to obtain halftone gradation when converting the digital image signal (indicating the density value) into a binary value and forming an image using a laser beam printer, etc. By converting the signal into a signal and comparing the converted signal with a periodic pattern signal such as a triangular wave, a binarized signal subjected to pulse width modulation is generated.

FIG. 8 shows an example of a circuit block diagram for realizing this method.

Digital image input signal 816 is latched by latch circuit 801 in synchronization with video clock 811. This video clock 811 is a clock obtained by dividing the frequency of the master clock 812 by two using a flip-flop 804 to J-. still,
It is assumed that the master clock 812 is synchronized with the horizontal synchronization signal 813 in advance. Here, the horizontal synchronization signal 81
3 may be generated internally or given externally, and if this device is applied to a laser beam printer, it may be a well-known beam detect (BD) signal, for example. There may be.

Now, the digital image signal of the latch circuit 801 is converted into an analog image signal by the D/A converter 802 and input to one input terminal of the comparator 803.

On the other hand, the master clock 812 is frequency-divided to a predetermined period by a frequency divider 805 and a period switching signal, and further divided by two by a J- flip-flop 808, with a duty ratio of 50.
% clock signal 814. This clock signal 81
4 and the period of the video clock 811 is determined by the frequency divider 80.
This corresponds to a frequency division ratio of 5. Furthermore, since the frequency divider 805 is loaded with a frequency division ratio by the OR signal of the horizontal synchronization signal 813 described above and the ripple carry oud (RCO) signal of the frequency divider 805, the image signal 815 and the clock signal 815
This means that each line is completely synchronized. Clock signal 814 is input to pulse pattern generator 810 through buffer 809, converted into a triangular wave, and matched with the dynamic range of image signal 815. Note that the pulse pattern generator 810 is composed of a well-known integrating circuit composed of, for example, a resistor and a capacitor, a buffer amplifier for dynamic range adjustment, and the like. And a pulse pattern generator 810
The triangular wave pattern signal outputted from the comparator 803 is input to the other input terminal of the comparator 803 and compared with the analog image signal 815, and pulse width modulation of the image signal 815 is performed. That is, the digital image signal 816
A pulse signal having a width corresponding to the value of is generated.

[Problem to be solved by the invention] However, in this way, pulse width modulation is performed,
Even if a photoreceptor is irradiated with laser light and printing is performed using developer material (toner), due to the nature of the laser, photoreceptor, and toner, toner will adhere to the area around the laser irradiation spot.
Therefore, the overall image becomes darker than expected, and especially in high-density gradations, that is, gradations close to black, all are black, resulting in poor gradation as a whole.

The present invention has been made in view of this problem, and it is an object of the present invention to provide an image processing device that makes it possible to obtain an image with excellent gradation without producing a blackish image as a whole.

[Means for Solving the Problem] In order to solve this problem, the present invention includes the configuration shown below.

A pulse width modulation signal based on the value of the multivalue pixel data is generated by comparing sequentially input multivalue pixel data with a pattern signal of a predetermined period, and a beam to the photoreceptor is generated based on the pulse width modulation signal. An image forming apparatus that forms a visible image by controlling the irradiation time of the image forming apparatus includes a converting means for converting the multi-value pixel data into multi-value pixel data with a low density value, and energizing the converting means at every predetermined pixel period. A biasing means is provided.

[Operations] In the configuration of the present invention, the density value of input multivalued pixel data is converted to a lower value at every predetermined pixel period. Then, pulse width modulation processing is performed on the converted multi-value data and the non-converted multi-value data to form a visible image.

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

1. Description of the outline of the configuration (FIG. 1)> FIG. 1 shows a specific configuration related to pulse width modulation processing in this embodiment.

The digital image signal 116 (4 bits=16 gradations) becomes a signal 117 via the image signal processing circuit 118 and is taken into the latch circuit 101. Other operations are as known.

In the case of the embodiment, the digital image signal 116 is 4 bits, so the input data is O'-FM (H is a hexadecimal number).
The value is larger (smaller) than white (black).
It shows data close to .

FIG. 2 is a detailed diagram of the image signal processing circuit 118, and the third
The figure is a timing chart.

In Figure 2, 123 is a negative edge trigger.
A flip-flop divides the frequency of the video clock 111 (see signal 31 in FIG. 3) into two and outputs the result as a VIDEO mask signal 124 (see signal 32 in FIG. 3).

In addition, the 4-bit multivalued digital image signal 116 (see signal 30 in FIG. 3) is converted to VIDE by OR gates 119 to 122.
The signal 117 is logically summed with the O mask signal 124 and
The signal is input to the latch circuit 101 as a signal. Therefore, every other signal 117 takes on a value of "F)I (white)" (see signal 33 in FIG. 3).

The latch circuit 101 receiving this signal 33 outputs the signal 34 to the D/A converter 102 in synchronization with the video clock 31. As a result, the D/A converter 102 outputs the signal 35 shown in FIG. 3 to one input terminal of the comparator 103.

Further, the other side of this comparator 103 has a triangular wave 3.
6 is input, the pulse width modulation (PWM) signal output from the comparator 103 becomes like the signal 37 in FIG.

Thereafter, based on this signal 37, a laser drive circuit (not shown) controls the lighting of the semiconductor laser, etc., and printing processing is performed by applying known electrophotographic technology.

The output results based on the principle of this embodiment will be explained using FIGS. 4(a) and 4(b).

In addition, in both FIGS. 4(a) and (b), 3 pixels in a row are "4N"
This figure shows the case where a digital image signal of 1 is input, and FIG. 11A shows an example using the conventional method, and FIG.

As can be seen by comparing Figures 4(a) and (b), in the past, when printing a density close to black, adjacent pixels are connected, and the digital image signal changes. However, the density will be expressed as black, resulting in an overall blackish print.

On the other hand, in the case of this embodiment, PWM conversion processing is not performed for every other pixel, so the output pixels are not connected to each other, the gradation is maintained even when the color is close to black, and the overall It is possible to make it brighter.

Explanation of the second embodiment (Figures 5 and 6) In the embodiment described above, every other pixel is set to white data, but when the density exceeds a certain level, the data becomes black data instead of white data. You may also do this.

FIG. 5 shows another circuit configuration of the image processing circuit 118 in this case, and FIG. 6 shows input digital data and its output results in this configuration.

Also in the illustration, the input digital image signal 116 is
“FM” is applied to every other pixel by IDEO mask signal 124
In other words, white data is used, but when the value of the image signal 116 at the timing of masking is "OH", the data is output as is instead of being set to "Fs". This is achieved by the illustrated OR gate 125 and AND gate 126.

That is, when the logic of the VIDEO mask signal 124 is "1" and the value of the manually input digital image signal is "0.4", the output of the AND gate 126 becomes "O".

Therefore, it is possible to obtain results as shown in FIG. This can be clearly understood by applying it to an image in which a halftone image such as a photograph and a binary image such as a character line drawing are mixed together.

In other words, when such an image is input, it is only "ON" for text and line drawings (input data is "0").
(black) “, and for halftone images, every other pixel “
FH (white)" is output, so it is possible to obtain results with no unevenness for text and line drawings, and excellent gradation for photographic images. In this case, the input digital image signal Although we have explained the case where masking is not performed when is "OH", it is of course okay to provide a width that satisfies this limit value.For example, if the input digital image signal is 8 bits (256 tones) In some cases, it may be configured such that "if the number is 10 or less, no masking is performed".

Description of the third embodiment (Fig. 7) In the configuration shown in Fig. 1, a latch is provided before the image signal processing circuit 118 that latches the input digital image signal and outputs it from a video clock of twice the frequency. establish. Then, the image signal processing circuit 118 outputs VIDEO of twice the frequency.
The process shown in FIG. 2 is performed using the mask signal, thereby printing DATA and white data (FH) within one input digital image signal as shown in FIG. According to this embodiment, it is possible to obtain an image with good gradation and print density.

As described above, according to this embodiment, when reproducing a halftone image, at least the entire image does not appear blackish, and it is possible to obtain an image with excellent gradation.

In the embodiment, it was determined whether to mask every other pixel, but the present invention is not limited to this.

That is, masking may be performed at intervals of two pixels or more.

[Effects of the Invention] As explained above, according to the present invention, the density value of the input pixel is changed at predetermined intervals so that the result becomes white.
At least the entire image does not appear blackish and it is possible to obtain an image with excellent gradation.

Furthermore, if the conversion to a lower density direction is stopped when the density value of the input multi-valued data is high, it becomes possible to reproduce a good mixed image of character line drawings and halftone drawings.

[Brief explanation of drawings]

FIG. 1 is a block diagram of pulse width modulation processing in an embodiment. Fig. 2 is a diagram showing the specific contents of the image signal processing circuit according to the embodiment, Fig. 3 is a timing chart for explaining the image processing contents, and Fig. 4 (a) shows an example of a conventional output pixel. Figure 4 (b
) is a diagram showing an example of output pixels in the embodiment, FIG. 5 is a diagram showing specific contents of the image signal processing circuit in the second embodiment, and FIG. 6 is a diagram showing input image data and output pixels in the second embodiment. 7 is a diagram showing the relationship between the timing chart of the image signal in the third embodiment and the resulting output pixel, and FIG. 8 is the circuit configuration related to general pulse width modulation processing. FIG. In the figure, 101...Latch circuit, 102...D/A converter, 103-Z), 104, 108 and 123...Flip-flop at J-, 105... Frequency division device, 110... pulse pattern generator, 119-1
22...OR gate. (: , J11ζ゛-゛(a) Figure 4 Figure 6 Figure 8

Claims (2)

[Claims] (1) A pulse width modulation signal based on the value of the multivalue pixel data is generated by comparing sequentially input multivalue pixel data with a pattern signal of a predetermined period, and a pulse width modulation signal is generated based on the pulse width modulation signal. In an image forming apparatus that forms a visible image by controlling the irradiation time of a beam, the image forming apparatus comprises: a converting means for converting the multi-value pixel data into multi-value pixel data with a low density value; An image forming apparatus characterized by comprising a biasing means for biasing the image forming apparatus. (2) The image forming apparatus according to claim 1, further comprising a deactivating means for deactivating execution of the converting means in accordance with the density value of the input multivalued pixel data.