JPS61256864A - Picture reader - Google Patents

Abstract

PURPOSE:To simplify a circuit constitution and to reduce cost by detecting a white reference start position and a black reference start position by the variation of a picture signal level for a density reference without using a switch or a sensor. CONSTITUTION:A density reference 1 is arranged in a beltlike in the sequence of a black reference 20, a white reference 19 and the black reference 20 and a detection for a white reference and a black reference is executed using a white reference 17 and a black reference 18 which are arranged at the outside of the setting area of an original 2. The reflected light of the density reference 1 which is irradiated by a light source 3 is condensed by a lens 4 and through a solid-state image pickup element 5, an amplifier 6 and and A/D converter 7, an addition averaging circuit 9 performs the addition averaging calculation of picture signals for share of the number of picture elements which are set at a dip switch 8. A differential discriminator 11 calculates the difference between the output signal of a 1 line delay circuit 10 and that of the addition averaging circuit 9 and inputs it to a comparator 13. When the calculated result of the difference is larger than the setting value at a dip switch 12, the position is decided as the start positions of the black references 18 and 20 and when it is smaller, the position is decided as those of the white references 17 and 19.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an image reading device using a solid-state image sensor such as a caD.

BACKGROUND OF THE INVENTION When reading a document using a solid-state imaging device such as a conventional COD, a fluorescent lamp is used. However, fluorescent lights have the characteristic that the center is bright and the ends are dark. In addition, the lens that collects the reflected light from the document from the light source also has the characteristic that the center is bright and both ends are dark.
Even when a document with uniform density is read, a shading problem occurs in which the output image signal level from a solid-state image sensor such as a COD is not constant. Various methods have been considered to solve this problem.

There is a method of attaching a reflective plate between the light source and the document, and a method of attaching a reflector plate to both ends of the fluorescent lamp.

However, while this method is effective for lenses that do not change over time, it cannot guarantee against fluctuations in power supply, temperature changes, and deterioration due to lifespan in fluorescent lamps, so it is not possible to always obtain a stable output signal. There is also the problem that it takes time and effort to make adjustments such as replacing the fluorescent lamp. In order to solve this problem, a method was devised in which a white reference is read immediately before scanning the document, shading characteristics are extracted from the white reference data, and correction is performed using the data.

(For example, Japanese Unexamined Patent Publication No. 59-226668, etc.) According to this method, the shading characteristics at the time of reading a document can be corrected, so it is also effective in correcting fluorescent lamps that change over time. Also, in order to improve the S/N ratio of the image signal,
It has been considered to perform noise removal using data obtained by reading the black reference.

Problems to be Solved by the Invention In the above-mentioned apparatus, a switch or a sensor is used to determine whether the solid-state image sensor has read a white reference, a black reference, or an actual document. therefore,
The problem was that the circuit configuration was complex and the cost was high.

The present invention solves the above problems of the prior art, and aims to detect the white reference start position and the black reference start position without using switches or sensors.

Means for Solving the Problems The present invention provides a density standard having at least one white standard and one black standard provided near the document and arranged in a line in the sub-scanning direction; information reading means for reading information on the original and the density reference; and n read by the information reading means when the information reading means is reading the density reference sound (where n is an integer of 1 or more).
a comparison means for comparing an average value for an image signal of a certain number of pixels before main scanning with an average value for an image signal of a certain number of pixels currently being read; The above object is achieved by providing a determining means for determining whether a white standard or a black standard of the density standard is being read.

Operation The present invention has the above configuration, and detects the white reference starting position and the black reference starting position by reading a certain type of density reference and monitoring the change in the image signal level.

EXAMPLE An example of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram of an image reading apparatus according to an embodiment of the present invention, and FIG. 2 is a diagram showing the arrangement of white and black density standards.

In FIG. 1, 1 is a density standard provided on the scanning table;
2 is a document; 3 is a light source that illuminates the density reference 1 and the document 2; 4 is a lens that collects reflected light from the density reference 1 and the document 2; and 5 is a lens that converts the light collected by the lens 4 into an analog image signal. A solid-state image sensor such as COD, 6 an amplifier that amplifies the output image signal from the solid-state image sensor 6 such as COD, 7 a Mu/D converter that converts the analog image signal output from the amplifier 6 into a digital image signal, 8 is a dip switch that sets the number of pixels to perform the averaging operation, 9 is a dip switch 8
An averaging circuit that calculates the average number of pixels set in 1.
0 is a one-line delay circuit that synchronizes the output of the averaging circuit 9 with the output of the next averaging circuit 9, and 11 is a difference device that calculates the difference between the output signals of the averaging circuit 9 and the one-line delay circuit 10. , 12 is a dip switch for setting a value to be compared in magnitude with the output of the difference device 11, 13 is a comparator for comparing the set values of the difference device 11 and the dip switch 12, and 14 is a sign bit in the output data of the difference device 11. An inverter that inverts the logic; 15 is an AND gate that calculates the AND of the output signals of the difference device 11 and the comparator 13; and 16 is an AND gate that calculates the AND of the output signals of the comparator 13 and the inverter 14. .

In FIG. 2, 17 is a white reference placed outside the original setting area, 18 is a black reference placed outside the original setting area, and 19 is a white reference placed outside the original setting area.
is the white reference, and 20 is the black reference.

The operation of the above configuration will be explained below.

Prior to scanning the original 2, the reflected light of the density reference 1 irradiated by the light source 3 that scans the density reference 1 each time is collected by a lens 4, and converted into an analog image signal using a solid-state image sensor 5 such as a COD. The signal is amplified by an amplifier 6 and converted into a digital signal by a MU/D converter 7.

As shown in Fig. 2, the density standards 1 are arranged in a band shape in the order of black standard, white standard, and black standard, and are arranged in the following order in the main scanning direction: (,
The length is longer than the maximum width that can be read by the solid-state image sensor 5 such as a CD. Also, usually the OCD is smaller than the setting area of original 2.
The readable range of the solid-state image sensor 6 is larger.

Using this, the white reference 17 and the black reference 18 placed outside the setting area of the original 2 are used to detect the white reference and the black reference.

In order to improve the SIN ratio of the image signal and perform accurate determination, it is effective to perform an arithmetic average calculation of the image signals of a plurality of strokes. The DIP switch 8 is set with the number of pixels to be subjected to the averaging operation, and the averaging circuit 9 selects the number of pixels set in the DIP switch 8 from among the image signals of the white reference 17 or the black reference 18. Performs signal averaging calculation.

The white reference position and the black reference position are determined based on the level difference between the two lines in the sub-scanning direction. Therefore, in order to compare the average value of the read image signal with the average value of the image signal of the next line, it is necessary to delay the output timing of the averaging circuit 9 by one line processing. Let's do it.

The differentiator 11 calculates the difference between the output signal of the 1-line delay circuit 10 and the output signal of the averaging circuit 9, and outputs a signal with the number of bits of the input signal + 1) bits, the most significant bit of which is used as a code signal. The differentiator 11 subtracts the output signal of the averaging circuit 9 from the output signal of the one-line delay circuit 10. Note that the output signal represents the level difference between the previous line and the current line.

Comparator 13 compares the setting value of DIP switch 12 and the output signal of difference device 11 .

By the way, normally, the output signal for one line of the solid-state image sensor 5 such as COD has an amplitude of about 60% in the peripheral area compared to the central area due to shading, and the image signal amplitude of a black original is the maximum. It is a few percent of the amplitude. Therefore, the difference in the image signal amplitude between the white reference 17 and the black reference 18 is about 60% of the maximum amplitude of the image signal even in the peripheral area, so the dip switch 12 is set to 50% of the maximum amplitude of the image signal.
It is sufficient to set it to about 0%.

Now, if the difference result of the differentiator 11 is positive, then the differentiator 1
If the difference result of 1 is larger than the set value of the dip switch 12, it indicates that the image signal level has decreased significantly, and therefore it can be determined that the black reference 18.2° starting position is reached.

Next, if the difference result of the differentiator 11 is negative, the difference result of the differentiator 11 is expressed as a two's complement number, so if the value is smaller than the setting value of the dip switch 12, the image signal level will be too high. It shows that the white standard has increased by 17.
It can be determined that this is the starting position of No. 19.

From the white reference start position and black reference start position detected in this way, the white reference 19 and the black reference 2o are determined, respectively.

Ingest data.

After that, the original 2 is scanned.

As described above, according to this embodiment, by providing a density reference composed of a white reference and a black reference, and a means for detecting the white reference position and black reference position of the density reference, the white reference can be detected without a switch or sensor. The starting position and the black reference starting position can be detected.

Note that the above functions can also be implemented using software such as a microcomputer, and if performed using software such as a microcomputer, the burden on the hardware can be further reduced.

In addition, in this embodiment, the one-line delay circuit 10 calculates the difference between the white or black reference additive average value read one line before and the currently read black or white reference additive average value. The line delay circuit 1o has n lines,
For example, the average value of two or three lines before may be held and the difference may be calculated.

Effects of the Invention As described above, the present invention provides a density reference having a certain fixed format and means for detecting a white reference position and a black reference position from the density reference without using a switch or a sensor. It is possible to solve the problems of complicating the circuit and increasing costs caused by specifying the starting positions of the white reference and black reference used for shading correction and noise removal using switches or sensors,
The effect is great.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of the image reading load in one embodiment of the present invention, and FIG. 2 is a layout diagram of white and black density standards. 1...Concentration standard, 9...Additional averaging circuit, 10...1 line delay circuit, 11...
・Differentiator, 13... Comparator, 15.16...
...and gate, 17...white reference outside the original setting area, 18...black reference outside the original setting area,
19...white standard, 2o...black standard.

Claims (2)

[Claims] (1) A density standard provided near the original and having at least one white reference and one black reference arranged in a line in the sub-scanning direction, and information about the original and the density standard using reflected light from a light source. information reading means for reading, and when the information reading means is reading the density standard, n (where n is an integer of 1 or more) read by the information reading means with respect to an image signal of a constant number of pixels before main scanning; a comparison means for comparing the average value with an average value for an image signal of a certain number of pixels currently being read; and the information reading means determines whether the density standard is a white reference or a black reference, depending on the comparison result of the comparison means. An image reading device comprising: a determining means for determining whether reading is being performed. (2) The comparison means calculates the difference between the average value for the image signal of a constant number of pixels before n main scans and the average value for the constant number of pixels currently being read, and then sets a threshold for the difference value taking shading into consideration. The image reading device according to claim 1, wherein the image reading device is compared with the following.