JPS6145677A - Digital copying machine - Google Patents

Abstract

PURPOSE:To strengthen a contrast of a picture with partial density contribution by converting a picture signal so that a maximum value and a minimum value of the picture signal for every page may respectively correspond to the maximum value and the minimum value of gradation in a recording part. CONSTITUTION:A picture signal read by an image sensor 1 is converted to a digital signal by an analog/digital converter 2 and data for one page are stored at a page memory 3. The digital signal is successively inputted to a hold means 4. At the hold means, a maximum value and a minimum value are held and inputted to a gradation converting circuit 5. At the gradation converting circuit 5, to expand the digital signal up to gradation width which can be reproduced in a memory part 6, the digital signal read from the page memory 3 is converted to gradation and is sent to a recording part 6.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a digital copying machine, and more particularly to a digital copying machine equipped with a gradation conversion function for improving contrast and obtaining sharp image output.

[Prior art]

In digital copying machines, various gradation conversion methods have been considered based on image signals in order to perform better recording. However, these methods all perform gradation conversion according to a predetermined table.

[Problem that the invention seeks to solve]

By the way, in the conventional digital copying machine as described above, when copying an image with a biased density distribution, only a part of the gradation width that can be reproduced is used in the recording section, and the recording means cannot be used effectively. , there was a problem of low output contrast.

The present invention has been made in view of the above-mentioned circumstances, and an object of the present invention is to enhance the contrast of an output image and improve the image quality.

[Means for solving problems]

In order to achieve the above object, the present invention is provided with a hold means for recognizing and storing the maximum and minimum values of image signals to be recorded such as original reading signals for each page, and also for storing the maximum and minimum values. , are each provided with a gradation converter that converts the image signal so as to correspond to the maximum and minimum gradation values in the recording section, so that the gradation width of the recording section can be utilized to the fullest extent.

[Effect]

That is, as an example of its basic configuration is shown in FIG. 1, an image signal read by an image sensor 1 is determined by an analog-digital converter (A/D converter) 2 based on a predetermined threshold value. A digital signal representing the gradation corresponding to which of the gradations corresponds to i is converted, and data for one page is stored in the page memory 3.

On the other hand, the digital signals are sequentially input to the holding means 4. In this holding means, the held value and the newly input digital signal are successively compared and updated, and only the maximum and minimum values are held. is input. Here, the digital signal read from the page memory is subjected to gradation conversion so as to widen the digital signal to a gradation width that can be reproduced in the recording section 6, and then sent to the recording section.

For example, when the density distribution (gradation distribution) of a digital signal before gradation conversion of a certain image is as shown in Figure 2, the gradation is adjusted so as to fully use the recordable gradation width, as shown in Figure 3. The image signal is quantized appropriately so that the tone conversion is performed and the density distribution of the image signal is widened.

〔Example〕

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

As shown in FIG. 4, this digital copying machine includes an image sensor 11 for reading image information on the original by detecting reflected light from the original, and an image signal read by the image sensor 11. an analog-to-digital converter (A/D converter) 12 that performs digital conversion according to a predetermined threshold value and determines a gradation level;
A page memory 13 stores the gradation level signal outputted from the converter ν page by page, and the gradation level signal is sequentially held, and two values, the maximum value and the minimum value thereof, are always held. By successively comparing that value with the input gradation level signal and updating the maximum and minimum values, when the gradation level signal for one page is input, the maximum value of that page is calculated. and a maximum/minimum hold circuit 14 configured to hold the minimum value, and a digital-to-analog converter (D/A converter) for analog converting the gradation level signal output from the page memory 13. 15, the analog-converted signal here, the maximum and minimum values of the gradation level of the page output from the maximum/minimum hold circuit 14, and the maximum and minimum values of the gradation level of the recording section 16. An analog-to-digital converter (A/II:
converter) 17. And recording section 16
In this case, printing energy is determined based on the recording level signal to form a halftone image.

Here, the analog-digital converter 17 makes the maximum and minimum values of the gradation level of the page correspond to the maximum and minimum values of the recording level, respectively, and quantizes them at equal intervals. .

For example, in this device, one pixel is divided into four micropixels, two dots of different sizes are made to correspond to each micropixel, and from the combination of these four micropixels, the dots shown in Fig. 5 (1) to As shown in (9), it is possible to record nine gradations. The maximum value of the gradation level signal of a certain page is shown in Figure 5 (3
), and the minimum value is the gradation level shown in Figure 5 (7), the digital signal output from the page memory is once converted into analog by the D/A converter, , an A/D converter associates the maximum level with gradation level (9) and the minimum level with gradation level (1), and quantizes the intermediate level at equal intervals. That is,
The read signal is converted from level (3) to level (1), level (5) to level (5), level (7) to level (9), and is output from the analog-digital converter 17, leaving the read signal unchanged. If recorded, Figure 6 (a)
The page that is supposed to look like this is reproduced as shown in Figure 6(b), and as is clear from these comparisons, it is clear that according to the present invention, the contrast is increased and the image becomes sharper. be.

In the embodiments, a digital copying machine has been described, but it goes without saying that the present invention is also applicable to other digital recording devices, including recording printers such as facsimile machines.

Regarding gradation conversion, we made the maximum and minimum values of the recording level correspond to the maximum and minimum values of the density level of the image signal of that page, and quantized them at equal intervals. For the gradation level assignment of
The method is not limited to this method.

〔Effect of the invention〕

As described above, according to the present invention, the present invention includes a hold means for recognizing and storing the maximum and minimum values of image signals to be recorded, such as read signals, for each page, and also stores the maximum and minimum values. Each is equipped with a gradation converter that converts the image signal to correspond to the maximum and minimum gradation values in the recording section, and the gradation width of the recording section is utilized to the fullest, so the density distribution Even if the image is biased, it is possible to strengthen the contrast and record it as a sharp image.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the basic configuration of the digital copying machine of the present invention, FIG. 2 is a diagram showing the density distribution of the digital signal before gradation conversion, and FIG. FIG. 4 is a diagram showing the density distribution of the converted digital signal; FIG. 4 is a diagram showing a digital copying machine according to an embodiment of the present invention; FIGS. Diagram (a)
6 is a diagram showing a part of an image recorded by a conventional digital recording device, and FIG. 6) is a diagram showing a part of an image recorded by a digital recording device according to an embodiment of the present invention. 1... Image sensor, 2... A/D converter, 3.
. . . page memory, 4 . . . hold means, 5 . . . gradation conversion circuit, 6 . Memory, 14...Maximum/minimum hold circuit, 15...D/A
Converter, 16... Recording section, 17... A/D converter.

Claims (1)

[Claims] a page memory for storing one page worth of image signals; a hold means for detecting and holding maximum and minimum values of pixel gradation values of the image signal when writing the image signal to the page memory; and a gradation converter for converting the gradation so that the maximum and minimum values of the gradation of the image signal held in the holding means correspond to the maximum and minimum values of the recordable gradation, respectively. A digital copying machine characterized by: