JP2647397B2 - Image processing device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention compares a multi-level image data with a pattern signal of a predetermined period, generates a pulse width signal corresponding to the density of the multi-level image data, and generates a pulse width signal. The present invention relates to an image processing apparatus that forms an output image based on the image.

[Prior Art] Conventionally, a digital copying machine or the like is a typical device of this type. Normally, in this apparatus, each pixel data (for example, 1 pixel = 8 bits = 256 gradations) read by an image input device such as an image scanner is made to correspond 1: 1 to a pixel to be printed out.

[Problems to be Solved by the Invention] When an image is formed by such processing, for example, as shown in FIG. 4A, the period of the image at the time of reading by the image input device and the period of the image input device A phase shift from the sampling pitch occurs, and image data including a stripe pattern is sometimes formed. This is a so-called moiré phenomenon. In particular, when processing such as edge enhancement is performed, moiré appears strongly in an image.

Further, in the case of using an image input device with an increased sampling (to increase the number of pixels for reading) in order to remove phase moire generated at the time of inputting an image, a light receiving element array, an optical system, and the like become complicated. However, it became very expensive and had practical problems.

In addition, a smoothing process may be performed to eliminate moire. However, adverse effects such as deterioration of resolution may occur.

Furthermore, even if edge enhancement is performed after smoothing in order to improve the resolution, the noise component is also enhanced this time, so that the image looks rough.

The present invention interpolates input multi-valued image data, generates multi-valued image data of a plurality of pixels corresponding to one pixel of an output image by the input pixels and the interpolated pixels, and outputs the multi-valued image data of the plurality of pixels and the output. A pulse width signal is generated by comparing a pattern signal corresponding to one pixel of the image, and an image having an output width corresponding to the generated pulse width signal is output, thereby obtaining a good image from which moiré has been removed. It is an object of the present invention to provide an image processing device that can be used.

[Means for Solving the Problems] To solve this problem, the present invention has the following configuration.

That is, the multi-valued image data is compared with a pattern signal of a predetermined period to generate a signal having a pulse width corresponding to the density of the multi-valued image data, and output in an image processing apparatus that forms an output image based on the signal. Input means for inputting multi-valued image data of a plurality of powers, interpolating at least one pixel between all the input pixels and a common number of pixels between the pixels, and Interpolating means for generating multi-valued image data of a plurality of pixels corresponding to one pixel of the output image by using the obtained pixels; multi-valued image data of a plurality of pixels corresponding to the pixels of the output image from the interpolating means and one pixel of the output image A comparison unit that compares the pattern signal corresponding to the pulse width signal with the pattern signal corresponding to the pulse width signal, and an output unit that outputs an image having an output width corresponding to the pulse width signal generated by the comparison unit.

[Operation] In the configuration of the present invention, at least one pixel between the pixels of the multi-valued image data input and a common pixel between the pixels are interpolated, and the input pixel and the interpolated pixel form one pixel of the output image. The corresponding multi-valued image data of a plurality of pixels is generated by the interpolation means. Then, the generated output image 1
The multi-valued image data of a plurality of pixels corresponding to the pixel is compared with a pattern signal corresponding to one pixel of the output image, and a pulse width signal is generated by a comparing unit. The output unit outputs an image having an output width corresponding to the pulse width signal generated in this manner.

Embodiment An embodiment according to the present invention will be described below in detail with reference to the accompanying drawings. In this embodiment, the density level signal of the copying machine, especially the read pixel, is pulse width modulated, and the pulse signal is used to control the driving of the laser unit while forming a series of processes such as forming, developing, and fixing an electrostatic latent image. A description will be given of the apparatus that performs the processing.

<Description of Main Configuration (FIG. 1)> FIG. 1 is a diagram showing a configuration relating to video signal generation of a digital copier in the embodiment.

In the figure, reference numeral 1 denotes an image reading unit for reading a document image, and outputs a signal of a voltage level corresponding to the density. Reference numeral 2 denotes an analog signal per pixel output from the image reading unit 1
An A / D converter 3 for converting the digital data into bits (= 256 gradations) receives the digital pixel data, and an interpolation processing unit 3 (which will be described later in detail) interpolates between the pixels. Reference numeral 4 denotes a D / A converter for converting digital pixel data output from the interpolation processing unit 3 into a voltage level signal. This analog signal is output to a “+” input terminal of a comparator 7. Reference numeral 5 denotes a pattern signal generator for generating a triangular wave, and this signal is output to the "-" input terminal of the comparator 7. The comparator 7 sets the output to “1” when the voltage level output from the D / A converter 4 is higher than that of the triangular wave (“0” otherwise). The signal output from the comparator 7 is used as a drive signal for a laser unit (not shown), and the emitted laser light is irradiated onto a photosensitive drum via a known polygon mirror and f-θ lens, and Form a latent image. Thereafter, processing such as development, separation, and fixing is performed.

Reference numeral 6 denotes a clock generator for inputting the reference frequency.
Based on f ₀ , the clock of the clock number f _R is read by the image reading unit 1.
And a double clock number (= 2 · f _R ) to the interpolation processing unit 3.

<Description of Interpolation Processing Unit (FIGS. 2 and 4)> In general, there is a sampling theorem that "an image sampled at twice or more the highest frequency of the original image can be restored." This means that the original image can be restored by convolving the SINC function with the sampled image data. In other words, moiré will also disappear. However, the SINC function is (However, x [mm] and f [lines / mm].) Since it is a continuous function, it cannot be directly used for digital signal processing.

Therefore, in the embodiment, the input image is fixed in advance so as to interpolate twice.

 Hereinafter, the processing contents of the interpolation processing unit 3 will be described.

The image data 20 output from the A / D converter 2 is developed as image data 21 on a buffer (not shown) in the interpolation processing unit 3. At this time, since the number of clocks to the interpolation processing unit 3 is twice as large as that of the image reading unit 1, the number of clocks is expanded every other as shown in the figure. In addition, a one-row matrix 22 (si
nc function) is stored in advance, and image data 23 is obtained by calculating “0” data in the image data 21, that is, the pixel density of the even address.

For example, the pixel density c _{n + 2} is c _{n + 2} = a _n −b ₋₅ + a _{n + 1} · b ₋₃ + a _{n + 2} · b ₋₁ + a _{n + 3} · b ₁ + a _{n + 4} · b ₃ + a _{a n + 5 · b 5 =} 50 · 0.127 + 200 · (-0.212) +200 · 0.637 +50 · 0.637 + 20 · (-0.212) +20 · 0.127 ≒ 121.

In addition, other c _{n + k} can be determined by similar calculation. In this way, the interpolated image data 23 is as shown in FIG. 4 (b), and it can be seen that moiré is reduced as compared with that of FIG. 4 (a).

<Explanation of Video Signal Generation (FIGS. 3 and 5)> Based on the above principle, a video signal generation process in the configuration of FIG. 1 will be described.

After the above processing is performed by the interpolation processing unit 3, the signal is converted into an analog signal again by the D / A converter 4 and output to the “+” input terminal of the comparator 7. Meanwhile, a triangular wave synchronized with the clock number f _R from the pattern signal generator 5 is the comparator 7 - is outputted to the input terminal "". The comparator 7 compares these two input signals, and outputs a "1" signal as a video signal when the input level of the input terminal is true, and outputs a "0" signal when the level is false. ,
This situation is illustrated in FIG.

In the figure, 30 is a signal output from the D / A converter 4, and 31 is a triangular wave. A comparison result 32 is a signal having a pulse width corresponding to the pixel density (hereinafter, referred to as a PWM signal).

A laser unit (not shown) is driven and turned on based on the PWM signal generated in this manner, and an electrostatic latent image is formed on the photosensitive drum.

In this case, the number of pixels output as a video signal is the same as the number of pixels read by the image reading unit 1 irrespective of the fact that the interpolation processing has twice expanded. That is, the image is doubled at the time of interpolation and compressed by half at the time of output, thereby forming an output image of the same size.

Incidentally, the clock number of the pattern signal generator 5 in the embodiment has been with f _R, for example, as shown in FIG. 5, at all be supplied with clock number of the same 2 · f _R and the interpolation processing unit 3 I do not care.

By the way, in order to further suppress the moiré, the interpolation processing unit 3 inserts two or more pixels between input pixels and performs interpolation using a sinc function. However, in this case, it is necessary to change the contents of the matrix 22 according to the number of inserted pixels, and it is necessary to supply the interpolation processing unit with clocks of the number of clocks corresponding to the inserted pixels.

As described above, according to the present embodiment, it is possible to form a good output image without moire generated from the sampling period when reading a document image.

[Effect of the Invention] As described above, according to the present invention, input multi-valued image data is interpolated, and multi-valued image data of a plurality of pixels corresponding to one output pixel is generated by the input pixel and the interpolated pixel. By comparing the multi-valued image data of the plurality of pixels with a pattern signal corresponding to one pixel of the output image, generating a pulse width signal, and outputting an image having an output width corresponding to the generated pulse width signal, A good image from which moiré has been removed can be obtained.

[Brief description of the drawings]

FIG. 1 is a schematic diagram of a configuration for generating a video signal in the embodiment, FIG. 2 is a diagram for explaining the contents of an interpolation processing unit in the embodiment, and FIG. 3 is a diagram illustrating the principle of pulse width modulation in the embodiment. FIG. 4 (a) is a diagram for explaining the principle of occurrence of moiré at a sampling period when reading an image, and FIG. 4 (b) is a diagram showing that moiré is reduced by the interpolation processing of the embodiment. FIG. 5 is a diagram for explaining the principle of pulse width modulation in another embodiment. In the drawing, 1 ... image reading unit, 2 ... A / D converter, 3 ...
... interpolation processing unit, 4 ... D / A converter, 5 ... pattern signal generator, 6 ... clock converter.

Claims (1)

(57) [Claims] An image processing apparatus for generating a signal having a pulse width corresponding to the density of multivalued image data by comparing the multivalued image data with a pattern signal having a predetermined period, and forming an output image based on the signal. Input means for inputting multi-valued image data of a plurality of pixels to be output; at least one pixel between all of the input pixels and a common number of pixels between the pixels, and input. Interpolating means for generating multi-valued image data of a plurality of pixels corresponding to one pixel of the output image by using the pixels and the interpolated pixels; multi-valued image data of a plurality of pixels corresponding to one pixel of the output image from the interpolating means; A comparison unit configured to compare a pattern signal corresponding to one pixel of an image to generate a pulse width signal; and an output unit configured to output an image having an output width corresponding to the pulse width signal generated by the comparison unit. The image processing apparatus according to claim Rukoto.