JPS60128329A - Background density detecting device - Google Patents

Abstract

PURPOSE:To detect exactly a density of a background by adding a run-length of the same picture density, and setting a picture density corresponding to the run-length having the largest addition result, as a background. CONSTITUTION:A scanning motor 22 executes scanning of an original platen or an optical system, and a position sensor 23 executes a detection of an area for detecting a background density. A picture signal 27 outputted from an image sensor 26 is digitized to three stages in accordance with a density of a picture element by an A/D converter 17, and sent out to a data bus 12. A CPU11 searches for the run-length at every picture element of the same picture density, and executes an addition processing of the run-length of the same picture density. As a result, the picture density corresponding to the run-length having the largest addition result becomes a background of an object original.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a background concentration detection device for detecting the background concentration of a document or the like.

[Prior art]

When copying with a copying machine, the density of the background (background or ground color) becomes a problem, especially for colored originals. For example, when a document created using a diazo copying machine is copied using an electrostatic copying machine, the background color is bluish, so the toner concentration in this area becomes high, making the copied image very difficult to read. Therefore, in electrostatic copying machines, techniques such as changing the bias potential of the developing device are used to reproduce the background as close to white as possible, thereby making the image clearer. Regarding the background, there is a similar problem with image reading devices using image sensors.

In some cases, the background is determined by relying on the intuition of the operator of the copying machine, and in other cases, the background density is detected using a background density detection device.

The former method has a problem in that it is not possible to individually adjust the background density in G)' apparatuses that do not involve a bud pellet, such as a copying machine equipped with an automatic document feed mechanism.

In the latter conventional background density detection device, a sensor is placed at a point other than the focal point, and the density of a blurred image is detected and regarded as the background density.

For this reason, when the proportion of black text information in an image increases, there is a problem in that the background density is detected to be quite high.

[Purpose of the invention]

In view of the above circumstances, an object of the present invention is to provide a background density detection device that can accurately detect the background density even in a document or an image that has a large proportion of text information. .

[Structure of the invention]

The present invention includes a scanning means for scanning an object whose background density is to be detected, a conversion means for converting the resulting image signal from analog to digital on a pixel-by-pixel basis, and A run length calculation means for calculating those run lengths, an addition means for adding run lengths of the same image density, and a comparison using the image density corresponding to the run length having the largest addition result as the background of the object. A background concentration detection device is provided with means for detecting a background concentration. The addition means may add only run lengths larger than a predetermined threshold level for each image density.

〔Example〕

The present invention will be described in detail below with reference to Examples.

FIG. 1 schematically shows the background concentration detection device of this embodiment. The CPU (central processing unit) 11 of this device has a data bus 12 and an address bus 1.
3 through RAM (Random Access Memory)
14, ROM (read only memory) 15, input/output capo) 16, and A/D converter 17. Several circuit components are connected to the human output port 16.

Of these, the lamp drive section 18 turns on the light source lamp 19 prior to copying. The motor drive unit 21 also controls the drive of the scan motor 22 to scan a document table or an optical system (not shown).

As a result, the document is scanned. The position sensor 23 is disposed on the document table or on the movement path of the optical system, and is used to detect an area for detecting background density. The sensor drive section 25 drives an image sensor 26 for density detection. The image sensor 26 is 17
It is a 28-bit linear sensor, and the image signal 27 outputted from it is amplified by an amplifier 28 such as an OP amplifier and supplied to an A/D converter 17.

The A/D converter 17 digitizes this into three stages depending on the density of the pixel and sends it to the data bus 12.

FIG. 2 is a flowchart for explaining the operation of the background concentration detection device configured as described above.

The print start button (
(not shown) is pressed, reading of the program stored in the ROM 15 is started, and the detection operation of the background concentration detection device is started.

First, the CPU II controls the lamp drive section 18-G to light the light source lamp 19. Then, the next data is written into a predetermined work area in the RAM 14 as initial data (step 2).

L=0, DL (old)=low, Lmax:=1 where L represents the run length. When L=0, the run length is 0. Further, DL represents the detected background concentration. Dt (old) refers to the old detected concentration, and DL (new) refers to the new detected concentration. The detected concentration is divided into three levels as described above. Dt"0, which is initially set, means that a specific pixel is at the white level as shown in FIG.
) is at an intermediate level as shown in DL = 2
means that the black level is reached as shown in FIG. Finally, Lmax refers to the maximum value of the run length. ``Initially, Lmax is set to a value of 1.

With the initial data set in RAM 14, motor 2
Move 2. This moves the reading area of the document. Also, under the control of the sensor drive section 25, the image sensor 26 starts scanning the document. When the scanning of the image sensor 26 reaches 1c, m from the leading edge of the document 31 shown in FIG. At the same time, the A/D converter 17 is triggered (step ■), and data acquisition in the density detection area 32 with a scanning width of 1 cm is started in units of pixels. New detected concentration DL (new)
It is determined whether (step ■) is equal to the old detected concentration DL (old) (step ■).

If both are equal (Yes), the content of run length L is increased by 1 (step ■). Then, the maximum value Lmax of the run length and its contents are compared (step ■
), if it becomes larger than the maximum value Lmax, this is replaced with the maximum value Lmax (step ■). Maximum value Lma
Until x is not reached (step ■; NO), the above-described operation is repeated, and the run lengths of pixels having the same detected density are measured.

When changing from background to character or vice versa, the detected density of the pixel becomes discontinuous. When the two detected concentrations DL (old) and Dt (new) are no longer equal (step ■; N0), the original detected concentration Dt (old) and its run length L are written to the concentration storage area of the RAM 14. (Step ■). Then, the new detected concentration DL (new) becomes the newly measured detected concentration (step 2), and the run length L is initialized to 0 again (step 0). In this state, run length measurement for the detected concentration DL (new) is started. When the image sensor 26 scans the entire density detection area in this manner, individual data regarding the detected density DL and the run length L are stored in the density storage area of the RAM 14. Also, the maximum value Lmax of the run length is decreased by the comparison operation.

FIG. 5 illustrates a case where the alphabet "S" is written in black on a white background in the concentration detection area. Part (A) of the figure shows how the alphabet "S" is read using 5x7 pixels. When one pixel completely corresponds to the black character area, the detected density DL is “
2”, and “0” if it completely corresponds to a white background.
becomes.

Further, in the intermediate case, the detection 194 degree DL becomes "1". First, when the detected densities of the five pixels constituting the first row are examined, the results are as follows.

DL=1.2.2.2.1 Therefore, if this is expressed as data of (DL, L), it will be as follows.

(1,'1)(2,3)(1,1) The second and subsequent lines can also be expressed as data in a similar format. Figure (B) shows the data that has been analyzed in this way.

When the data processing as described above is completed, the CPU 11 determines a threshold level for background density detection, and calculates the sum of run lengths for each detected density DL using this threshold level as a reference. Then, the detected concentration having the largest value is set as the background concentration.

FIG. 6 shows the flow of such work.

First, the following data is written as initial data into a predetermined area of the RAM 14 shown in FIG. 1 (step 0).

Lo"0, Ll=0, L2=0 Here, Lo refers to the run length at which the detected concentration Dt is 0". Similarly, L+ and Ls each have a run length with a detected concentration DL of 1 lxll or "2".

Next, the first data is loaded (step 0).

In the example shown in FIG. 5, it is (4, 1').

Next, it is determined whether the run length L in this data exceeds the threshold level (Step 1).

Step 0). In the example shown in FIG. 5, the maximum run length is 4. The threshold level is generally Lmax
−Lmax/2. In this example, L
max /~2 and its value is 4/2 or 2
becomes. The first data (1, 1) is 1 x 2 and does not exceed the threshold level (step @; N
o). In such a case, the next data (2, 3) is loaded (step 0). In this data, 3>
2 and exceeds the threshold level (step @
: Yes).

For data exceeding the threshold level, the run length is counted for each detected concentration. That is, it is first determined whether the detected concentration DL of the loaded data is "0" (step ■), and the run length is counted for each detected concentration. (Yes
), run length.

is added (step [phase]). If the detected concentration DL is different (step ■; No), then the concentration is “
1” (step [phase]).
1" (Yes), the run length L1 is added (step O). When it is not "1", that is, when the detected concentration DL is "2" (step [phase]; N
O), the run length L2 is added (step @).

After completing the addition work of three types of run lengths L, , L, , L2 for all data in this way,
CPLll,1 compares these added values. In the example shown in FIG. 5, each addition value is as follows.

ΣL,=14, ΣL,='0, ΣL,=9 The maximum value among these added values becomes the background density. In this example, DL-◯, that is, white, becomes the background density.

If the threshold level is not set, each additional value will be as follows.

ΣL,=14, ΣL−,=6, ΣL2=15, that is, D
i=2' (black) is mistakenly recognized as the background density.

Therefore, the threshold level needs to be set appropriately under various conditions such as the resolution of the device. The A/D converter also needs to have a resolution of about 16 gradations (4 bits), for example, if the document or image is composed of multi-gradation image information such as a photograph.

If the background density is detected, the CPLlll controls the motor moving unit 2/1 to return the document table or the optical system to the scanning start position. The copying operation or image reading operation is then started from this position. At this time, it goes without saying that image processing is performed according to the background density.

〔Effect of the invention〕

As described above, according to the present invention, the background density can be determined by electrical processing, so it is possible to clearly reproduce an image in which the shading is particularly unclear. Moreover, electronic equipment equipped with a computer does not require any special parts, and this device can be manufactured at low cost.

[Brief explanation of drawings]

The drawings are only for explaining one embodiment of the present invention.
The figure is a block diagram of the background concentration detection device, Figure 2 is a flowchart showing the flow for creating basic data for determining background concentration, and Figures 3 (A) to (
C) is an explanatory diagram illustrating three levels of detected density, FIG. 4 is a plan view showing the density detection area of a document, FIG. B) is a correspondence explanatory diagram showing data based on this image in correspondence, and FIG. 6 is a flowchart showing the flow of calculating the sum of each run length. 11...cpu. 14...RAM. 15...ROM. 17... A/D converter, 26... Image sensor, 31... Document, 32... Density detection area. Applicant Fuji Xerox Co., Ltd. Agent Patent Attorney Umeo Yamauchi Figure 1 11 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6

Claims (1)

[Claims] (1) A scanning means for scanning an object whose background density is to be detected, a converting means for converting the image signal obtained by this from analog to digital for each pixel; a run length calculation means that calculates the run lengths for each pixel of density, an addition means that adds run lengths of the same image density, and an image density that corresponds to the run length having the largest addition result, 1. A background concentration detection device, comprising: comparison means for determining a background concentration. 2. Adding means for determining a predetermined threshold level smaller than the maximum run length calculated by the run length calculating means based on the maximum run length, and adding only run lengths larger than this threshold level for each same image density. 2. A background concentration detection device according to claim 1, further comprising a background concentration detection device.