JPS63252743A - Image processor - Google Patents

Abstract

PURPOSE:To modulate a pulse width so that a sharp contrast intermediate tone image may be regenerated by providing a modulation means to modulate the width of the pulse of image data converted by a conversion information selected on the basis of a density characteristic value. CONSTITUTION:Image data of a single page stored in a memory 1 is read, for instance, the maximum and minimum densities of image data of a single page are sought, and conversion information groups of a table 3 corresponding to the densities are selected by a selection signal 12. When the maximum and minimum densities of image data 11 are set to '30' and '20' respectively, the density range of input image data converted as if it were expanded by the table 3 in such a manner that the density level '20' of the image data 11 is converted to density level '20', the density level '25' of the image data 11 to density level '30' and the density level '30' of the image data 11 to density level '40'-, if said maximum and minimum densities are converted to data 13 based on the maximum density of '40' and the minimum density of '20' by means of the table 3. Consequently, data 13 with an expanded density range is output from the table 3, and the data is output in the form of modulated pulse width from a pulse width modulation circuit.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an image processing device that performs pulse width modulation of an image signal.

[Prior Art] In conventional laser beam printers, in order to record a halftone image, an image signal is pulse width modulated by a pulse width modulator, and the laser is driven by this modulation signal to reduce the recording time of one pixel. was under control. The pulse width modulator directly modulates the density range of the input image signal, and furthermore, the density range of the output image of such a printer is
Because the density range of the printed image is limited by other physical factors, the density range of the printed image is often narrower than the density range of the original document.

[Problems to be Solved by the Invention] Therefore, if the change in density of the input image signal is small, the rate of change in density of the image data obtained by pulse width modulation will be minute, resulting in subtle and small changes in density of the image signal. could not be played.

Furthermore, when a document with a halftone image such as a photograph is input and reproduced, there is a problem that the halftone image is output as a halftone image with poor contrast.

The present invention has been made in view of the above-mentioned conventional example, and it is an object of the present invention to provide an image processing device that performs pulse width modulation that can reproduce halftone images with clear contrast in response to subtle changes in image information. purpose.

[Means for Solving the Problems] In order to achieve the above object, the image processing apparatus of the present invention has the following configuration. That is, a calculation means for inputting image data and calculating a density characteristic value, a storage means for storing a group of conversion information for expanding the density range of the image data, and a storage means for storing a group of conversion information for expanding the density range of the image data, and a calculation means for calculating the group of conversion information based on the density characteristic value. It includes a selection means for selecting one of them, and a modulation means for performing pulse width modulation of the image data converted by the selected conversion information group.

[Operation] In the above configuration, the calculation means inputs image data and calculates a density characteristic value, and based on this density characteristic value, one of the conversion information groups stored in the storage means is selected. This conversion information group converts the image data so as to expand the density range of the image data, and the modulation means operates to perform pulse width modulation of the image data converted using this conversion information group.

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

[Description of Image Processing Section (FIG. 1)] FIG. 1 is a block diagram showing the configuration of the image processing section of the image processing apparatus of this embodiment.

In the figure, 1 indicates a memory that stores image data 10 input from an external device. 2 reads the image data 11 from the memory 1, selects the code signal information group stored in the table 3 based on the maximum density and minimum density of the image data in the memory 1, and selects the code signal information group corresponding to the image data 11. A control unit that outputs data 16 to the table 3, and includes an MPU such as a microprocessor, a ROM that stores control programs and data for the MPU, and a RAM that is used as a work area for the MPU.

3 is a table for inputting the selection signal 12 and data 16 from the control unit 2, and selecting and outputting the corresponding code signal 13; for example, the code signal 13 is image data obtained by expanding the density range of the image data 11; It has become. Furthermore, data 1
6 may be the lower address of the table 3, and the selection signal 12 may be the upper address of the table 3. 4 is code signal 13
This is a pulse width modulation circuit (PWM circuit) that receives an input signal, performs pulse width modulation on a laser beam modulation signal, and outputs the pulse width modulation signal.A detailed block diagram of the circuit is shown in FIG.

[Description of Pulse Width Modulation Circuit (FIG. 2) FIG. 2 is a block diagram showing an example of the configuration of the pulse width modulation circuit 4.

Code signal 13 from Table 3 is a multi-bit digital image signal indicating the pulse width to be modulated and is synchronized to input clock 15 by timing matching circuit 20.
is input. Furthermore, this timing matching circuit 20 inputs a counting clock 25 and outputs a synchronous clear signal 26 and data 27. Counter 22 receives synchronous clear signal 2
6 is true, the count clock 25 is counted and a count value 28 is output.

23 is a coat converter which inputs the count value 28, converts it into step-like data 29, and outputs it; and a timing matching circuit 20.
data 27 and data 2 from code converter 23
9 is input to the comparator 21 in synchronization with the signal.

The comparator 21 digitally compares the data 27 and the data 29, and outputs the comparison result 30 as a binary signal. Comparison result 3
0 may include an unnecessary noise signal called a glitch that occurs at the time of data change. The glitch removal circuit 24 is a circuit for removing this glitch. This glitch occurs at the inversion timing of the counting clock 25, so input the counting clock 25 and
The glitch is removed at the timing of , and the pulse width modulated binary signal 14 is output.

[Operation Description (Figs. 3 and 4)] Fig. 3 is a flowchart of the image data conversion operation program stored in the ROM of the control unit 2. This program stores, for example, one page of images in the memory 1. After the data is stored, the process starts when an instruction to output image data is given.

First, in step S1, one page of image data 11 stored in the memory 1 is read out, and, for example, the maximum density and minimum density of the one page of image data are determined, and in step S2, the conversion information group of table 3 is correspondingly determined. Selection is made by selection signal 12. This selected information group is a data group provided in one-to-one correspondence to the input data 16 within the range defined by the maximum density and minimum density determined in step S1.

Now the maximum density of image data 11 in memory 1 is 30
``'', when the minimum density is ``20'', Table 3
Maximum density is ``40'', minimum density is ゛20゛°
An example of converting into data 13 is shown in FIG.

As is clear from FIG. 4, for example, the density level "'20" of the image data 11 corresponds to the "density level 20", and the density level "25°" of the image data 11 corresponds to the density level "'3".
0°°, the density level "30" of the image data 11 becomes the density level "40°", and so on, so that the density range of the input image data is expanded according to Table 3, so the original density The range-extended image data will be pulse width modulated.

When the conversion information group of Table 3 is selected in this way,
In step S3, the image data 11 is read from the memory 1, and in step S4, the corresponding data 16 is outputted to the table 3 from the control section 2. As a result, as described above, data 13 with an expanded density range is output from the table 3, for example as shown in FIG. 4, and is pulse width modulated by the pulse width modulation circuit 4 and output.

In this embodiment, the maximum density and minimum density of the image data are detected to select the conversion information group, but the invention is not limited to this. For example, the intermediate value of the density of the image data and the density of the image data are selected. By detecting the amplitude, selecting a group of conversion information based on this, and expanding the density, it is possible to output a halftone image with clear contrast.

As described above, according to this embodiment, by selecting the most suitable conversion information group for image density information, even if the change rate of the input image density is small, the density change rate is expanded and pulse width modulation is performed. By doing so, output image data with clear contrast can be obtained.

Further, if there is a part where the density change is particularly desired to be emphasized, by storing such data in the table 3 in advance, it becomes possible to perform partial density emphasis.

Further, by changing the conversion of data 11 and data 16 by the control unit, arbitrary density enhancement is possible.

[Effects of the Invention] As explained above, according to the invention, by converting image information and performing pulse width modulation to expand the density range of input image information, it is possible to obtain halftones with clear contrast. This has the effect that an output image can be obtained.

[Brief explanation of drawings]

Figure 1 is a block diagram showing the configuration of an image processing unit of an image processing device according to an embodiment of the wooden invention, Figure 2 is a block diagram showing the configuration of a pulse width modulator, and Figure 3 is one page of image data. FIG. 4 is a flowchart showing the conversion operation of FIG. 4, which is a diagram showing an example of density conversion of image data using a table. In the figure, 1...memory, 2...control unit, 3...table, 4...pulse width modulation (PWM) circuit, 12...
- Selection signal, 13... Code signal, 14... Binarization code, 15... Input clock, 20... Timing matching circuit, 21... Comparator, 22... Counter, 23・
... code converter, 24 ... glitch removal circuit, 25
... Counting clock, 26 ... Synchronous clear signal, 28
... Count value, 3° ... Comparison result. Table 11 Table 13 Figure 3

Claims (2)

[Claims] (1) Calculating means for inputting image data to calculate a density characteristic value; storage means for storing a group of conversion information for expanding the density range of the image data; 1. An image processing apparatus comprising: a selection means for selecting one of the above; and a modulation means for performing pulse width modulation of image data converted by the selected conversion information group. (2) The image processing apparatus according to claim 1, wherein the modulating means compares the image data with a reference digital signal and binarizes the image data.