JP2509565B2 - Image processing device - Google Patents

Description

TECHNICAL FIELD The present invention relates to an image processing apparatus which performs pulse width modulation and outputs binary image data.

[Prior Art] In a conventional image processing apparatus for processing a color image signal,
Three colors of yellow (Y), magenta (M), and cyan (C),
Alternatively, a color material of four colors including black (BK) is used, and the gradation expression is performed by pulse width modulation of the image signal to change the area of the pseudo halftone dot to obtain a full color print. However, the image information processed by such a color image processing apparatus includes, for example, a solidly colored image for identification in a graph or the like (a solid color reproduced image) or a subtle halftone such as a pictorial image. There is halftone image information that requires color image reproduction.

In the case of the former, the solid color is tightly solid and
There is no fog in the white area, that is, a high-contrast image output is required, but in the latter case, the highlight part is not too skipped and the dark part is not too crushed, and the image is reproduced with continuous gradation. That is, soft image output is required.

[Problems to be Solved by the Invention] However, since the properties of these images often conflict with each other, a processing system suitable for each image quality is required to perform these image processes, and the apparatus becomes complicated. There was a problem of becoming.

The present invention has been made in view of the above conventional example, and an object of the present invention is to provide an image processing apparatus capable of performing good image processing on any image.

[Means for Solving Problems] In order to achieve the above object, the image processing apparatus of the present invention has the following configuration.

That is, an image processing device for inputting digital image information, converting it into analog image information, and comparing it with a reference signal having a predetermined frequency to perform pulse width modulation of the analog image information, wherein the white level of the analog image information is And a second mode in which the signal level width of the black level is substantially equal to the amplitude of the reference signal, a second mode in which the signal level width is smaller than the amplitude of the reference signal, and setting means for setting the type of image. Equipped with.

[Operation] The image processing apparatus having the above configuration operates so as to perform pulse width modulation by switching between the first mode and the second mode corresponding to the setting means.

[Embodiment] An embodiment of the present invention will be described in detail below with reference to the accompanying drawings.

[Description of Image Processing Unit (FIG. 1)] FIG. 1 is a block diagram of the image processing unit of the laser beam printer of the embodiment. Reference numeral 1 denotes a digital data output device, which is a CCD color sensor (not shown) or Perform color conversion, A / D conversion, etc. on the image data from the video camera,
Each pixel data is converted into digital data having density information of a predetermined bit, divided into each color component, and output. This digital data may be stored in memory,
It may be input from an external device by communication or the like.

When the color printing section prints sequentially for each color,
As shown in the figure, one of the color component signals Y, M, C and BK is selected by the selector 2 and input to the digital-analog converter (D / A converter) 3 to be converted into an analog amount.
The converted analog pixel signal 15 is sequentially input to one terminal of the comparison circuit 4.

On the other hand, the pattern signal generator 5 outputs the triangular wave pattern signal 16 at a cycle of once for every predetermined pixel of the digital data output from the digital data output device 1, and inputs the triangular wave pattern signal 16 to the other terminal of the comparison circuit 4. To do. Reference numeral 7 is an oscillator for generating a reference clock signal 19. Reference numeral 8 denotes a timing signal generating circuit, which counts down the clock signal 19 from the oscillator 7 in synchronization with the horizontal synchronizing signal 17 from the horizontal synchronizing signal generating circuit 6, for example, at every 1/4 cycle to generate a pixel clock 9
And the screen clock 10 and the like described later are output.

The pixel clock 9 is used for the transfer clock of the digital data and the latch timing of the D / A converter 3.
The horizontal synchronizing signal 17 may be internally generated or may be externally supplied.

In the present embodiment, since this apparatus is applied to a laser printer, the horizontal synchronizing signal 17 is a well-known beam detect (BD) signal generated for each line. In the comparison circuit 4, the analog-converted analog pixel signal 15 and the signal level of the pattern signal 16 are compared with each other, and pulse-width modulated 2
The binarized image data 18 is output.

Since the laser beam printer of this embodiment uses the image scanning method as the laser exposure method,
The analog pixel signal 15 is processed so that black and white are inverted before entering the comparison circuit 4. The pulse-width-modulated binary image data 18 is input to, for example, a modulation circuit for modulating a laser beam, and the output signal of the modulation circuit causes the laser to be turned ON / OFF according to the pulse width of the image data.
A halftone image is formed on the recording medium. This is Y, M, C, BK
A full-color print can be obtained by performing the above process on each signal and overlapping them. Reference numerals 20 and 21 are image mode input sections, which will be described later, and are used to change the output level of the analog pixel signal 15 or the pattern signal 16 according to the type of image data.
It is given to the A converter 3 or the pattern signal generator 5.

FIG. 2 is a timing chart for explaining the timing of signals at various parts of the apparatus shown in FIG.

The pixel clock 9 is a signal obtained by counting down the reference clock signal 19 by a quarter cycle by the timing generation circuit 8 and is output in synchronization with the horizontal synchronizing signal 17. The pixel clock 9 is input to the D / A converter 3 and the digital data output device 1 and is used as a pixel data transfer clock. The screen clock 10 is a signal obtained by counting down the pixel clock 9 output from the timing generation circuit 8 by the timing generation circuit 8. Here, the screen clock 10 is obtained by counting down the pixel clock 9 to a quarter cycle. The screen clock 10 is input to the pattern signal generator 5 as a synchronizing signal for generating a pattern signal 16 (for example, a triangular wave).

As is apparent from FIG. 2, the analog pixel signal 15 and the pattern signal 16 are compared by the comparator 4, and when the analog pixel signal 15 is larger, it is 0, and when it is smaller, the binarized image data 18 is created. And output.

As described above, the image processing apparatus according to the present exemplary embodiment performs almost continuous pulse width modulation by converting a digital image signal into an analog image signal and then comparing the analog image signal with a triangular wave having a predetermined period to obtain a high gradation property. The image output of high quality is obtained.

[Comparative Explanation of Image Binarization Mode] (FIGS. 3 and 4)] FIGS. 3 and 4 compare the analog image signal 15 and the pattern signal 16 in the solid color reproduction mode and the halftone reproduction mode, respectively. And pulse width modulated binary image data
It is a timing chart to get 18.

FIG. 3 shows the signal timing in the solid color reproduction mode. The white level 30 of the analog pixel signal 15 is shown in FIG.
Is the apex of the pattern signal 16 and the black level 31 is the pattern signal
It almost coincides with the bottom of 16. In the case of the laser beam printer of this embodiment, the laser lighting time is the binary image data.
The pulse width of 18 is almost the same, the laser does not light up at the white level 30 (this pulse width is PW0), and fully lights up at the black level 31 (this pulse width is PW1). Lights up and toner adheres to the developed portion, and development is performed.

FIG. 4 shows a case where the analog pixel signal 15 and the pattern signal 16 in the halftone reproduction mode are compared to obtain the binarized image data 18.

Here, the white level 33 of the analog pixel signal 15 is lower than the apex of the pattern signal 16, and the black level 32 is the pattern signal 16
The signal level of the analog pixel signal 15 is adjusted so that it becomes higher than the bottom of the. Therefore, even at white level 33, the laser slightly lights up (this pulse width is PW2), and at black level 32, the laser does not fully light up (this pulse width is PW3
And).

[Explanation of Sensitometry (FIG. 5)] FIG. 5 shows a laser beam printer for binarizing a pixel signal having a certain input level by performing almost continuous pulse width modulation by the above-mentioned image processing method. Input to the section to convert the exposure from laser light to the surface potential of the photosensitive drum,
Sensitometry showing the correspondence when converting the surface potential to the reproduced image density, where I0 to I3 are the input level values and PW
0 to PW2 is the pulse width of the above-mentioned binary image data 18, D0 to
D3 is a reproduced image density value, V0 to V3 are surface potentials of the photosensitive drums, and each attached numeral corresponds to each level.

In the halftone reproduction mode, since the gradation is emphasized, the relationship between the input level and the density needs to be linear.
50-53 of each curve in the figure between the △ and ○ marks 54-57
(I2 → PW2 → V2 → D2, I3 → PW3 → V3 → D3) is used. As shown in FIG. 4, the laser is slightly turned on with the pulse width PW2 even at the white level 33, and the pulse width of the binarized image data 18 becomes PW3 at the black level 2 so that the laser is not fully turned on. .

On the other hand, in solid color reproduction mode, it is necessary for the density to be high and the color to be hard to fog, so points 58 to 59 in FIG.
Part surrounded by 59 (I0 → PW0 → V0 → D0, I1 → PW1 → V1 → D
Use 1). In this case, since the reproduced images are colored differently, it is suitable for a solid image such as a graph using a color for identification.

The level can be switched between the halftone reproduction mode and the solid color reproduction mode by using the image mode input section 20 in the D / A exchanger 3 shown in FIG.
Input the signal from. Thus, in the halftone reproduction mode, the output level width of the analog pixel signal 15 is the pattern signal.
It is preferable that the level width be smaller than the level width of 16 so that the analog pixel signal level width is substantially equal to the level width of the pattern signal 16 in the solid color reproduction mode.

Although the image forming unit has been described as a laser beam printer using an image scanning method in the above embodiments, it may be a laser beam printer using a back ground scanning method. It may be a printer using a method, for example, LED or LCD.

Further, although the level of the analog image signal is changed in the solid color reproduction mode and the halftone reproduction mode in the above embodiment, the level of the pattern signal 16 may be switched on the contrary. 21 is connected to the pattern generator 5 in FIG. 1 to switch the output level of the pattern signal 16 as described above.

Further, in the above embodiment, the levels of the analog image signal and the pattern signal 16 are simply switched in the solid color reproduction mode and the halftone reproduction mode, but in addition to this, the screen ruling may be switched at the same time.

The reason for this is that the image becomes sharper as the screen ruling becomes larger, but the gradation becomes worse. When the screen ruling is small, the gradation is good, but the sharpness is lost. Therefore,
If you reduce the screen frequency in solid color playback mode and increase the screen frequency in halftone playback mode,
The image quality required by the above-mentioned partner is satisfied.

Further, in the present embodiment, only the case of color image processing is shown, but when both halftone reproduction and solid reproduction are required, it is of course effective for monochromatic image signal processing.

As described above, according to this embodiment, it is possible to realize switching of image modes satisfying the image quality required for solid color reproduction and halftone reproduction with a simple configuration.

[Effects of the Invention] As described above, according to the present invention, by changing the pulse width modulation signal according to the type of image, it is possible to obtain a good reproduced image with a simple configuration.

[Brief description of drawings]

FIG. 1 is a block diagram of an image processing apparatus according to an embodiment of the present invention, FIG. 2 is a timing chart of signals of various parts of the apparatus according to the embodiment, and FIG. 3 is an analog pixel signal and a pattern signal during solid color reproduction. Timing chart of binarized image data, FIG. 4 is a timing chart of analog pixel signals and pattern signals and binarized image data during halftone reproduction, and FIG. 5 is a diagram of input level and output density and binarized image data. It is a sensitometry showing correspondence of pulse widths. In the figure, 1 ... Digital data output device, 3 ... D / A converter, 4 ... Comparator, 5 ... Pattern signal generator, 6 ...
Horizontal sync signal generator, 7 ... Oscillator, 8 ... Timing signal generator, 9 ... Pixel clock, 10 ... Screen clock, 15 ... Analog pixel signal, 16 ... Pattern signal, 17 ... Horizontal sync Signal, 18 ... Binary image data, 19 ... Reference clock signal, 20, 21 ... Image mode input section.

Claims (4)

(57) [Claims] 1. An image processing apparatus for inputting digital image information, converting it into analog image information, and comparing the analog image information with a reference signal having a predetermined frequency by pulse width modulation. A first mode in which the signal level widths of the white level and the black level of the image signal substantially match the amplitude of the reference signal, a second mode in which the signal level width is smaller than the amplitude of the reference signal, and an image type are set. An image processing apparatus comprising: setting means, wherein pulse width modulation is performed by switching between the first mode and the second mode corresponding to the setting means. 2. D / A conversion means for converting digital image information into analog image information, said D / A corresponding to setting means.
The image processing apparatus according to claim 1, wherein the output level of the converting means is changed. 3. The image processing apparatus according to claim 1, wherein the output level of the reference signal is changed corresponding to the setting means. 4. The first mode is a solid color reproduction mode,
The image processing apparatus according to claim 1, wherein the second mode is a halftone reproduction mode.