JPS6145678A - Picture signal processing device - Google Patents

Abstract

PURPOSE:To obtain a easy-to-see picture considering density characteristics of an original by converting a picture signal by means of a temperature converting function which is calculate by a density histogram and a picture emphasizing degree designating signal of respective picture elements of the original. CONSTITUTION:By irradiating an original 1 with light from a light source 2, a reflection light is read by an image sensor 3 and a picture signal is obtained. The picture signal is digitized by an analog digital converter 4 and a gradation signal is obtained. The gradation signal is inputted through a change-over switch to a histogram generator 5 and a density histogram for one page is prepared. Based upon a picture emphasizing degree designating signal generated by selecting an operation panel 6, a density converting function is calculated from a histogram. At a density converter 8, the gradation signal is converted by the density converting function. Based upon an output of the density converter 8, printing is executed at a recording part 9.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an image signal processing device, and particularly to an image signal processing device equipped with a gradation conversion function for improving image quality.

[Prior art]

To adjust the recording density in copying machines such as xerography,
By giving instructions on the operation panel, the amount of donor supplied could be increased or decreased, and the overall concentration could be increased or decreased, such as ``dark,'' 1 normal, 1 light, etc. By the way, Research on pattern recognition using computers is an attempt to realize the flexible pattern recognition ability of humans using machines, and in recent years, active research has been progressing in image processing in particular.Digital image processing is
0 image quality improvement, 2. The purpose is to extract features, calculate minute amounts of a-'p', etc. Even in digital copying machines, various tone conversion methods have been devised to record better halftones based on image signals. However, all of these methods perform gradation conversion according to a predetermined table, and for images with distinctive density distributions, the contrast may become too strong and the image may appear hard. The contrast was too weak and the image often appeared soft, making the image look less than K<.

[Problem that the invention seeks to solve]

The present invention has been made in view of the above-mentioned circumstances, and there is a problem in that when all originals are tone-converted according to a predetermined table, the contrast becomes too strong or too weak, resulting in poor image quality. This is an attempt to solve the problem.

That is, it is an object of the present invention to provide a digital copying machine that takes into account the density characteristics of originals and can obtain images that are easy to view.

[Means and operations for solving the problem] In order to solve the above problem, the present invention creates a density histogram of each pixel of the original from the input image signal, and also combines this histogram with a predetermined A density conversion function is calculated based on the image enhancement degree designation signal emitted by the means, and the image signal is converted into a recording signal having an appropriate density level using this density conversion function, and an intermediate image is recorded from the recording signal by a predetermined recording means. Processed to reproduce a tonal image.

A density histogram is a bar graph in which the horizontal axis represents density and the vertical axis represents the number of pixels having that density. For example, the second (
a) As shown in the figure, when the reading signal of a certain original has a peak at a certain density of gray (intermediate color) in the histogram, that is, when there are extremely many pixels with density in a certain density area, the frequency of appearance of that density area is Because it is so high, it is difficult to see small changes in the image. In such a case, the second (b)
) As shown in the figure (), by performing density conversion so that each density area has an equal frequency, the frequently occurring density areas are divided into smaller parts, the image is emphasized, and the image becomes easier to see.

Further, even if the histogram of the read signal is uniform as shown in FIG. 3(a), it may be difficult to see. In such a case, a soft image can be obtained by dividing the high density and low density parts into smaller parts and weakening the contrast by making the density follow a lognormal distribution, as shown in Figure 3 (1)). be able to.

〔Example〕

A digital copying machine according to an embodiment of the present invention will be described below.

As shown in FIG. 1, this digital copying machine includes a signal reading unit that illuminates an original 1 with light from a light source 2 and reads the reflected light with an image sensor 3, and an image sensor 3 that reads the reflected light. An analog-to-digital converter (A/D converter) 4 for digitizing the signal based on a predetermined threshold value to obtain a gradation signal indicating a desired density; input,
An image generated by the histogram generator 5 that generates a density histogram for one page and the button selection of the selection switch on the operation panel 6! 7! an arithmetic circuit 7 that calculates a density conversion function from the histogram generated by the histogram generator 5 based on the +i preparation level designation signal;
Then, by switching the changeover switch, the same original 1 is scanned again by the image sensor, and the image signal obtained is digitized in the same manner as above, and the obtained gradation signal is converted into a density signal calculated by the arithmetic circuit. It is comprised of a density converter 8 that performs conversion using a function f(χ), and a recording section 9 that prints an output signal of the density converter as a recording signal.

If a selection is made on the operation panel such that the image enhancement degree designation signal becomes strong, for example, as shown in Section 2(b), each density area has the same frequency over the entire density area, The density conversion function y=f(χ
) is calculated, the arithmetic circuit 7 is configured.

In other words, the density characteristics of the original that are input as image signals are converted to the second (+!L) by the histogram generator.
If the histogram shown in the figure is generated,
The cumulative density frequency t of this document is as shown in FIG. 4(a). This fourth (→) Divide the cumulative frequency t shown on the vertical axis of the figure into equal parts, transfer the cumulative frequency t to the vertical axis of Figure 4(b), and set the horizontal axis as the converted concentration y, with a slope of 101 Next curve y=
t, and transfer the corresponding χθ value to the horizontal axis of FIG. 4(C), and the curve connecting these intersection points is the concentration conversion function y = f (z).

This can also be determined by the following equation.

When the histogram of the read darkness signal is expressed as h(χ), the cumulative frequency t is Cχ: concentration before conversion) Concentration to be converted 7 = f (2) Concentration function h' (7) Then, h'(7)=a(2nd(b)
(see figure).

Therefore, since the overall density is the same both before and after conversion, it should be noted that if the density widths used for both χ and y are the same, then $1 ax l, and if a>i, , the density width after conversion becomes narrower, and when a×1, the density width after conversion becomes wider.

Furthermore, when the contrast of the document is high and it is difficult to see, when the operator selects a weak image enhancement level designation signal on the operation panel, as shown in FIG. 3(b),
The arithmetic circuit 7 is configured to obtain a density conversion function y=f(z) such that the histogram after conversion has a lognormal distribution, the contrast is weakened, and a soft image is obtained.

That is, when the histogram generated by the histogram generator 5 covers the entire density region as shown in FIG. 3(a) and has the same frequency in each density region, the cumulative frequency is as shown in FIG. 5(a). It becomes a linear curve, but when the histogram after transformation takes a lognormal distribution,
Since the cumulative frequency is as shown in Fig. 5(b), from these, as shown in Fig. 5(C) II, as in the above case, <y=
K is set to find Rχ).

In addition, it is now possible to specify five levels of image enhancement on the operation panel, and the density conversion function is determined by the image enhancement degree based on this specification and the histogram generated by the histogram generator. It is configured to perform density conversion according to the density characteristics of the original.

According to this configuration, the degree of emphasis of the image can be adjusted according to the density characteristics of the original, and an easily viewable image can always be obtained, thereby improving the image quality. A preliminary scan was performed to create a density histogram, but the histogram was created and written to the page memory in one scan, and after the scan was completed and the histogram was created, it was read from the page memory. You can do it like this.

Further, regarding the calculation of the density conversion function, the density histogram to be converted is not limited to those shown in the embodiments, and can be selected as appropriate.

〔Effect of the invention〕

As described above, according to the present invention, a histogram regarding the density of each pixel of a document is created from an input image signal, and a density conversion function is created using this histogram and a desired image enhancement degree designation signal. The image signal is converted into a recording signal with an appropriate density level using this density conversion function, and a halftone image is reproduced from the recording signal by a predetermined recording means, so that the density characteristics of the original are It becomes possible to obtain an easy-to-see image in accordance with the desired degree of image enhancement and in accordance with the density characteristics of the document.

[Brief explanation of drawings]

FIG. 1 is a block diagram of an image signal processing device according to an embodiment of the present invention, FIG. 2(a) is a diagram showing a histogram showing an example of density characteristics of a document, and FIG. 2(b) is a diagram showing a histogram to be converted. FIG. 3(a) is a diagram showing a histogram of the state (uniform distribution), and FIG.
Figure (b) is a diagram showing the histogram of the state to be converted (log normal distribution), Figures 4 (a) to 4 (C) are from Figure 2 (a) to Figure 2 (b) n. Figure 5(a) showing the construction for determining the concentration conversion function (Figure 4(C)) of
Figures 5(c) to 5(c) are 3(a) to 3(b).
FIG. 4 is a diagram showing a plot for obtaining a density conversion function (m 5 (C) diagram) to a diagram. l... Original, 2-... Light source, 3... Image sensor, 4... Analog-digital converter, 5-... Histogram generator, 6-... Operation panel, 7-...
Arithmetic circuit. Figure 1 h (zu) χ

Claims (1)

[Claims] A histogram regarding the density of each pixel of the document is created from the input image signal, and this histogram and
A density conversion function is calculated based on the image enhancement degree designation signal issued by a predetermined means, and using this density conversion function,
An image signal processing device characterized in that the image signal is converted into a recording signal having an appropriate density level.