JPS6145679A - Picture signal processing device - Google Patents

Abstract

PURPOSE:To record at a binary level which is always most suitable for an original by operating a binary level so that dispersion between a white area and a black area may be maximum, base upon a density histogram concerning respective picture elements of the original. CONSTITUTION:A reflection light from a light source 2 reflected by an original 1 is inputted through a lens system 3 to an image sensor 4 and a picture signal is obtained. The picture signal is amplified by an amplifier 5 and digitized by an analog digital converter 6. A density histogram is prepared by a histogenerator 7, and based upon the density, a binary level is calculated by a processing circuit. At a digital comparator 10, the picture signal is made binary by a binary level calculated by the processing circuit 8. At a recording part 11, recording is executed base upon an output signal of the digital comparator 10.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an image signal processing device, and more particularly to an image signal processing device equipped with a binarization level adjustment function.

[Prior art]

Conventionally, in facsimile machines or digital copying machines, image signals are converted into binary values when recording.
The setting of the binarization level, that is, the threshold value for binary output, is done either by specifying it on a fixed force 1 operation channel. [Problem to be solved by the invention] For example, when you want to copy a manuscript written in pencil, it is difficult to copy it correctly because the density of the drawing varies depending on the density of the pencil used and the pressure applied. Similarly, it is not easy to record copies of newspapers and the like correctly, and it has not always been possible to record documents at the optimal binarization level.

[Means for solving problems]

In view of the above-mentioned circumstances, the present invention attempts to record a document based on the optimal binarization level, and creates a density histogram for each pixel of the document from the image signal.
Based on the histogram, a binarization level, that is, a threshold for binarization, that maximizes the inter-region variance between the white area and the black area is calculated, and the image signal is converted to a binary value based on the binarization level. It was designed to be digitized and recorded.

[Effect]

That is, in the present invention, as shown in the basic configuration in FIG. 6, an image signal carrying image information to be recorded is digitally converted by an analog-to-digital converter (A/D converter) 101, and is stored in a page memory, for example. At the same time, a density histogram of the original is created by the histogram generator 103.From this histogram, the density histogram of the document is stored in
After calculating the value level in the arithmetic processing circuit 104,
In the binarization circuit 105, the image signal corresponding to each pixel to be recorded is read out from the page memory 102, and the two
The signal is binarized based on the digitization level and is pressed to be sent to the recording unit 106 as a recording signal.

Here, the quantization levels in the histogram generator are 1, 13, . The frequency (
When the number of pixels) is set to na, the following relational expression holds true.

Now, the binarization level (threshold level for binarization)
Two areas where k is one black area o1=(t~k)
and white area 0tJlc+1. ~8) and binarize each image signal, the following relational expression holds true: 0 (1 = 1) This is the average density value of the pixels in the black area, and the inter-area variance is therefore The arithmetic processing circuit 104 calculates k that maximizes the inter-area variance, 7-''(k), from the histogram created by the histogram generator 103, and performs the binarization level based on this value k. It will be done.

In this way, the optimum 2
Binarization is performed depending on the digitization level, making it possible to maintain a good recording state.

〔Example〕

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.As shown in FIG. The light is input to the image sensor 4 via the lens system 3, and is converted into an image signal. An analog-to-digital converter (MU/D converter) 6 that performs digital conversion via an amplifier 5, a histogram generator 7 that creates a density histogram for each page, and a density histogram created by the histogram generator 7. , an arithmetic processing circuit 8 that calculates the value of k as a binarization level at which the inter-area dispersion force) is maximized.
The output of the MU/D converter is switchably connected to the histogram generator 7 by a changeover switch 9, and the image signal is converted to a binary value by the binary level k calculated by the arithmetic processing circuit 8. The digital comparator 10 is configured to include a digital comparator 10 that converts the digital comparator 10, and a recording section 11 that records the output signal from the digital comparator 10 as a recording signal.

Furthermore, the arithmetic processing circuit 8 calculates an all-pixel average value calculation unit 12 that calculates the average value μ of all pixels on the page, and a probability ω of a black area when k is the binarization level. ω(k) calculation unit 1 that calculates the conversion levels 1 to B
μ(k) calculation unit 14 which similarly calculates 3 and the average density μ of pixels forming a black area for each quantization level 1 and sK.
The calculation unit 15 calculates the inter-region variance (d) from the calculated values of and, and the value of k when taking the maximum value and the maximum value of the calculated inter-region variance (d). Calculate r
The k value calculated here is input to the digital comparator 10 and set as the binarization level of the page.

Next, the operation of this digital copying machine will be briefly explained.

First, the reading thread R scans the document 1 for the first time.
1C, the read signal is amplified as usual, digitally converted and input to a histogram generator 7, where a density histogram for each page is created.

Figure 2 (→ shows a histogram of a certain character manuscript, where the horizontal axis shows the density and the vertical axis shows the frequency. Here, the density d is expressed in 16 gradations consisting of 1.2...-16. The total number of pixels is N - l The probability of being in the bear area ω(b).

The density average value μ of the pixels forming the black area), the inter-region variance,
(k) As shown in FIG. 2 (1)) is calculated, and a value of k of 1 (=9) is detected that maximizes the inter-area variance.

The value of k detected in this way is set as the reference value of the digital comparator as the binarization level.

On the other hand, after this, the second reading scan of the same page is executed again by the reading system RK, but at this time, the output of the MU/D converter 6 connected to the histogram generator 7 is transferred via the changeover switch 9. and is connected to the input of the digital comparator 8.

The image signal is then binarized in accordance with the binarization level in the digital comparator IO, and sent to the recording section as a recording signal.

Under this pressure, the printing section performs printing according to the optimum binarization level, with the density +1=1 to 9 being a black area and the density a=io to 16 being a white area.

In addition, in the case of a weather map in a newspaper, a histogram is created as shown in Figure 3 (a), but at this time as well, as shown in Figure 3 (b), the outside variance between areas is calculated and +=7 is detected when the variance is maximum, and optimal recording is performed.

As described above, according to this digital recording device, binarization can be performed according to the optimum value of the binarization level set according to the density characteristics of the document. The value of k that maximizes the interregional variance y, (k) was set as the binarization level, but if the maximum value of the interregional variance y, (k) is small, that is,
When the histogram is almost uniform at each density level, it may be regarded as a halftone image, and the image may be quantized using a predetermined dither pattern without being binarized. In other words, for example, as shown in Fig. 4. As shown in FIG. 1, the function of dithering the image signal according to a predetermined dither pattern is achieved by arranging the digital comparator 1o and the parallel dithering circuit 20 of the digital copying machine of the embodiment shown in FIG. Here, the comparator 2) determines whether or not the 2 maximum values MAX detected by the 2 maximum value detector 16 are greater than the 2 reference values A preset. Based on the comparison result, the selector 22 selects either the dither signal output by the dithering circuit 20 or the binary signal output by the digital comparator IO as a recording signal in the recording unit. I'm busy deciding what to output. For example, when the maximum value of 2 is smaller than the 2 reference value A, that is, when it is outside MAX (A), the selector 22 outputs the dither signal converted by the dither circuit 20 as a recording signal. In addition, in the embodiment, prior to one normal reading scan, a reading scan was performed as a preliminary scan for creating a histogram, and a total of two scans were performed, as shown in FIG. By connecting the page memory 30 to the histogram generator 7 in parallel, the image signals are stored in the page memory 30 until the creation of the histogram is completed, and the digital copying machine is read out sequentially from the page memory 30. (The processing may be performed in the scanner 10, and in this case, only one reading scan is required.) [Effects of the Invention] As described above, according to the present invention, each of the originals is processed from the image signal. A density histogram corresponding to each pixel is created, a binary level is calculated based on the density histogram at which the inter-area variance between the white area and the black area is maximized, and the image signal is converted into a binary level based on the binarization level. Since the original document is automatically recorded, optimal recording is always possible for the original document.

[BRIEF DESCRIPTION OF THE DRAWINGS] FIG. 1 is a block diagram of a digital copying machine according to an embodiment of the present invention, and FIGS. A diagram showing one example of histogram and inter-area variance, Figure 3 (su) is a diagram showing another example of the same density histogram and inter-area variance, and Figure 4 is a block diagram showing another embodiment of the present invention. 5 is a block diagram showing still another embodiment of the present invention, and FIG. 6 is a diagram showing an example of the recording apparatus of the present invention. 101-A/D converter, 102... page memory, 103... histogram generator, 104
-...Arithmetic processing circuit, 105/Binarization circuit, 1...Original, 2...Light source, 3...Lens system, 4...
...Image sensor, 5...Amplifier, 6-A/D
Converter, 7--Histogram generator, 8-- Arithmetic processing circuit, 9-- Selector switch, 10-- Digital comparator, 11-- Recording section, 12--All pixel average value calculating section, l3. ...ω(k) calculation unit, 14
. . . to μ) calculation section, 15 . . . external calculation section, 16.
・Maximum value detection unit, 20... dithering circuit, 2)-・
-Comparator, 22-...Selector, 30...Page memory. Figure 2 (0) Figure 2 (b) Figure 2 (b)

Claims (4)

[Claims] (1) A histogram generator that creates a density histogram for each pixel of the document from the image signal, and from the created density histogram, calculates a binarization level that maximizes the inter-area variance between white and black areas. An image signal processing device comprising: an arithmetic processing circuit; and a binarization circuit that binarizes the image signal based on the binarization level. (2) The arithmetic processing circuit includes a comparator that determines whether the maximum value of the inter-region variance is less than or equal to a predetermined value, and is further connected in parallel to the binarization circuit, It is equipped with a dithering circuit that quantizes the image signal according to a predetermined dither pattern, and the output of the dithering circuit or the binary value is determined depending on whether the maximum value of the inter-area variance is less than or equal to the predetermined value. An image signal processing device according to claim 1, wherein the output of the conversion circuit is output as a recording signal. (3) connected in parallel to the histogram generator;
Any one of claims (1) and (2), characterized in that it comprises a page memory for storing image signals, and enables creation of a histogram and writing to the page memory in one scan. An image signal processing device according to claim 1. (4) The histogram generator and the binarization circuit are switchably connected to the image signal, and during the first scan as a preliminary scan, the image signal is connected to the histogram generator, According to any one of claims (1) to (2), the image signal is connected to the binarization circuit during the second document reading and scanning. Image signal processing device.