JPS59189783A - Picture signal processing system - Google Patents

Abstract

PURPOSE:To make each line binary without requiring a picture signal preserving memory nor auxiliary scanning by changing successively the threshold level of a prescribed scanning line on a basis of the texture density, which is detected in scanning before scanning of the prescribed scanning line, to make the line binary. CONSTITUTION:The detected texture level of the first main scanning line and the threshold for binarizing the i-th main scanning line are denoted as Wi and Si respectively. When scanning is started, a CPU 208 outputs S1=(3F(HEX)-W0)Xk +W0 to the first line. In this equation, 0<k<1 is true, and 3F(HEX) is a density level for the darkest of each picture element after A/D conversion. Since picture informatin before the first line does not exist, W0=0 is supposed for the first line. After the first line is made binary by the level S1, the CPU 208 takes in a texture level W1 in the first line, for which scanning is just terminated, synchronously with a synchronizing signal and outputs S2=(3F(HEX)-W1)Xk for the purpose of binarizing the second line. Hereafter, the i-th line is binarized with Si=(3F(HEX)-Wi-1XK+Wi-1similarly.

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field The present invention relates to an image signal processing method for binarizing an image R in real time.

Prior Art As a conventionally known image signal processing method, the threshold level is calculated by a statistical method based on both signals currently being read from the original, and the image signal is stored in memory and the threshold level is calculated. There is a method in which the image signal is later read out from the memory and binarized at the respective threshold level.

This method has the disadvantage that it requires a large amount of memory because it is necessary to temporarily store the image signal.

Another known method is to pre-scan the original, statistically determine the threshold level, and then convert it to 2x1σ during the main scan, but this method requires scanning the original twice, which is time-consuming. There was a drawback.

In addition, when converting to 2 Tsukuda with a fixed threshold level,
Neither memory nor preliminary scanning is required, but in this case it may not be possible to separate the background part and the information part.

OBJECTS In view of the above-mentioned points, an object of the present invention is to provide an image signal processing method that does not require an image signal storage memory or preliminary scanning, and can perform binarization appropriately.

In order to achieve such an object, the present invention includes a means for detecting the background density level in the scanning line of the document image area, and detects the background density level of the predetermined scanning line based on the background density detected in the scanning before the scanning of the predetermined scanning line. The symbol level is sequentially changed and binarized.

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

FIG. 1 is a schematic diagram of a document reading device for a copying machine to which the present invention is applied. Here, the original 102 is placed on the original table 101 and is held down by the original cover 110. Then, in order to read the image information of the document 102, a light source 10
The illumination light from 4 is reflected on the 102nd surface E of the original, and
05,1013.10? The image is then formed on the image sensor 103 via the lens 108.

Light source 104. Mirror 105 and mirrors 108 and 107 are moved at a relative speed of 2:1. This light source unit is
It is moved from left to right at a constant speed by a DC servo motor 109 under PLL (phase locked loop) control.

This moving speed is 90mm1 on the outward journey depending on the copying magnification.
sec (200%) to 380mm/5ec (50%
), and the speed is always 830 mm/sec on the return trip.

The image sensor 103 scans the main scanning line perpendicular to the sub-scanning direction in which the above-mentioned optical unit moves in a 113-pe sentence/
While reading with a resolution of mm, the optical unit is moved forward from the left end to the right end, and then moved back to the left end to complete one scan.

FIG. 2 shows a circuit for processing an image signal obtained from the image sensor 103. The image signal sent from the image sensor 103 is converted into a 6-bit digital signal by the A/D converter 201, and is sent to the latch 202. in synchronization with the clock. Latch 203. Latch 205. The signal is sent to comparator 204.

The comparator 204 compares the 6-bit image signal sent from the latch 202 with the image signal (6 bits) sent from the launch 203 one clock ago.

If the image signal sent from the latch 202 is smaller, the comparator output is sent to the AND gate 206. This AND gate 206 sends the comparator output from the comparator 204 to the latch 205 in synchronization with the clock.

The latch 205 sends the image signal sent from the latch 202 to the CPt 1208 in response to the comparator output. In addition to the comparator output and the clock, an enable signal indicating the valid period of the image signal sent from the image sensor +03 is introduced into the ant gate 20B. Then, the comparison result regarding the image signal of a predetermined section in the main scanning line is sent to the CPO 208 via the latch 205.
send to

On the other hand, as for the document cover 110, the side that presses the document is black-treated or mirror-finished.

Therefore, by capturing the image signal from the latch 205 in synchronization with the main scanning line synchronization signal, the CPO 208
Background density levels of various scanning lines can be detected.

CPO208 is based on the detected skin concentration level,
A threshold level is determined for each scanning line using an algorithm described later, and threshold level information is sent to the comparator 207 in synchronization with the main scanning line synchronization signal. Comparator 20? Then, the image signal from the latch 203 and the threshold level information from the cPυ 208 are compared to generate a binarized signal.

The density level of each pixel after A/D conversion is given by 3 F (Hu) when it is the blackest, and 0 when it is the whitest. Similarly, the background level in each main scanning line and the threshold level for each main scanning line are also given as 0 to 3 F CHEX).

3 and 4 show the control procedure of this device. In other words, the threshold level of the main scanning line to be focused on is successively changed according to the background level of the main scanning line immediately before it! 1[Fi will be explained using FIGS. 3 and 4. In the following description, Wi indicates the background level detected for the i-th main scanning line, and S] indicates a threshold level for performing binarization on the i-th main scanning line.

When the optical system starts moving forward to scan the document, CPO20
8 is the threshold level for the first line.
Output W6. Here, k is a coefficient determined empirically in advance and falls within the range of 0<k<1.

Further, since no image information has been obtained for the first line before that, it is assumed that the background level of the imaginary O-th line is Wo=O.

In an actual manuscript, it is thought that there is usually no image information within a few millimeters of the tip and the background is exposed, so the assumption of 1o'=Q is not inconvenient.

In this way, the leading edge (first line) of the original is set to 2 by 31.
When the digitization is completed, the CPO 208 takes in the background level W of the first line that has just been scanned in synchronization with the line synchronization signal, and sets the threshold level for binarizing the second line as S2 = (3F(SEX) Wl)
Output as X k.

Hereinafter, the threshold level 4 S of the i-th line is similarly set.
i = (3F(+-IEK)-Wl-x) X k
+W+-1 to perform 2-direction conversion. This binarization continues until the optical system finishes scanning the document and reaches the right end.

As described above, the background level of the i-1th line that has just been detected is used as the predicted value of the background level of the i-th line that is about to be scanned, and the detected background level and black Level 3Fa+
During u), the threshold level is determined by an empirical method and a second correction process is performed. As a result, it is possible to set an appropriate threshold level that follows density changes at the background level, make the background area white and separate it from the information area.Furthermore, it is possible to use it not only for preliminary scanning but also for image signal storage. memory is also no longer required.

Figure 5 shows the difference in binarization (S) using threshold level B that follows the density change of the background and fixed level A. In this figure, 5-1 is the image signal, and 5-2 is the background level. ,
5-3 shows a binarized signal by A, and 5-4 shows a binarized signal by B.

At fixed level A (A-3F/2=IF(1-11EX), it is not possible to separate the background part and the information part in the high background level part, but Si= (3F)I -Wl-1) The signal binarized using the threshold level B determined by
It is separated from part g.

Next, we will discuss another embodiment in which the background level of the main scanning line to be noticed is predicted based on the background level of several lines immediately before the main scanning line to be noticed, and the threshold level is determined accordingly. , will be explained with reference to FIGS. 6 and 7.

Among the n background levels detected for each of the n lines from the i-nth line to the +-1st line immediately before the main scanning line (i-th line) of interest, calculate the maximum and minimum values. The average value of the removed n-2 background levels is the estimated background level W of the i-th line to be scanned from now on.
Let it be i.

Using this estimated value Wi, the threshold level Si of the i-th line is set as 5i=-(3H(l(E)-Wi)*k+W
By setting k here to a coefficient determined empirically in advance so as to satisfy 0<k<1, the background level Wi is set to white and 2(lII), and the background part and the information part can be separated.

FIG. 6 is a flowchart showing the execution procedure.

First, in order to store n background levels, the area WBF is
+ or ItJBFn is prepared in RAM.

When scanning of the document is started, O is first set in these n areas (step 6-1). This results in
The background level of the imaginary n lines before the first line is assumed.

In response to the synchronization signal on the first line, wo is delayed (step 8-2.8-3). And the oldest data IIIBF stored in the n areas mentioned above.

Abandon WBF2, turn it into enemyBF, and turn 1jlBF3 into W B
In F2, . . . , WBFn is stored again in WBFh-engine, and the latest data Wo that has been fetched is stored in WBFn (step 6-4).

Then, these n pieces of data (WBF, or WBFn)
1. Calculate < L as described above, and further calculate W
.

Calculate Sl from (step 6-5.8-13).

Thereafter, in the same way, WBF, ~WBFn are updated line by line, and the threshold levels are updated to Sl, S3, etc. Step 6-7), z-value conversion is performed, and the optical system finishes scanning to the right edge of the document. At the point in time, the binarization process ends (step 6-8).

In addition, in Figure 7 is given by

With this method, it is possible to follow density changes at the background level, as in the previous '7) Example, without requiring any special memory for storing image signals, and without requiring preliminary scanning to determine the threshold level. By doing this, the background part can always be kept white and separated from the information part. Furthermore, by removing the maximum and minimum values of the background level data from multiple lines and averaging them, it is possible to eliminate errors caused by dust, flecks, or singular points on the document surface (for example, white spots) on the document table. Information can be removed and more accurate binarization can be performed.

Effects As explained above, according to the present invention, a means for detecting the background level of a main scanning line is provided, and while scanning a document, it is possible to detect the background level of one or more main scanning lines immediately before the main scanning line of interest. It is possible to predict the background level of the main scanning line of interest, determine the threshold level so that the predicted value is always white, and then binarize it, so memory for image signal storage and preliminary scanning are not required. By using a simple algorithm, it is possible to follow the density change at the background level of the document, separate the background part and the information part, and execute the binarization process.

[Brief explanation of drawings]

FIG. 1 is a schematic configuration diagram of a document reading device to which the present invention is applied;
Fig. 2 is a schematic diagram of the image signal processing circuit, Fig. 3 is a flowchart showing the control procedure of the first embodiment, Fig. 4 is an explanatory diagram of the first embodiment, and Fig. 5 is an image signal corresponding to the threshold level. FIG. 6 is a flowchart showing the control procedure of the second embodiment, and FIG. 7 is an explanatory diagram of the second embodiment. 101... Original table, 102... Original, 103... Image sensor, 104... Light source, 105.106,10? ...Mirror, 108...Lens, 109...DC servo motor, 110...Document cover, 201...A/D converter, 202, 203, 205...Latch, 204.2
0? ... Comparator, 206 ... AND gate, 20th ... CPU, A, B ... Threshold level, 5-1 ... Image signal, 5-2 ... Background level, 5-3. ...Binarized signal by A, 5-4...Binarized signal by B, 6-1 to 6-8... Control step. Patent applicant: Canon Co., Ltd. -567- Fig. 5-1 ゜Batter ■〜To゜. Figure 7

Claims (1)

[Scope of Claims] 1) A means for detecting the background density level in the scanning line of the fg draft image area is provided, and the thread of the predetermined scanning line described if・An image signal processing method that is characterized by sequentially changing the threshold level and converting it into two values. 2) The image signal processing method according to claim 1, wherein the threshold level is changed based on the background density level of each of the plurality of scanning lines immediately preceding the treasure scanning line. .