JP3348901B2 - Output non-uniformity measurement method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an output non-uniformity measuring method, and more particularly to an output non-uniformity measuring method capable of accurately determining partial output non-uniformity.

[0002]

2. Description of the Related Art As shown in FIG. 1, an image reading apparatus using an image sensor such as a CCD illuminates a document 1 with illumination 2 and forms an image of the document 1 on a light receiving portion of an image sensor 4 with a lens 3. Let me. The image information of the document 1 is photoelectrically converted by the image sensor 4 to become an electric signal, which is read. However, in general, even when the original 1 having the uniform density on the entire surface is read by this apparatus, the output signal of the image sensor 4 becomes as shown in FIG. 2 and is not uniform.
This is the image sensor 4 a large number of light receiving elements are arranged, that there are variations in sensitivity to that one by one, that the amount of illumination 2 are not uniform in the longitudinal direction, and, cos ⁴ rule This is because the amount of light transmitted through the lens 3 is smaller at the peripheral portion than at the central portion. For this reason, in the image reading apparatus, a plate for shading correction is provided or shading correction is performed electrically in order to make the output signal of the image sensor 4 uniform.
Regarding this, for example, the description in “CCD linear image sensor data book” (Semiconductor Sales Division, Semiconductor Business Division, Toshiba Corporation, issued in August 1991) can be referred to.

[0003]

In the shading correction described in the above prior art, a reference white plate is read,
This waveform is reproduced, multiplied and divided to obtain the output non-uniformity, and this phenomenon is corrected. However, in this method,
For example, irregularities as illustrated in FIG. 2 are generated in the output signal of the image sensor 4 due to dust and flaws attached to the optical components, or the influence of the partial output non-uniformity of the image sensor 4 itself. There was a problem that accurate output non-uniformity could not be measured. That is, even when the above-mentioned correction waveform is multiplied and divided at the time of reading a document, accurate shading correction cannot be performed. As a method for obtaining the partial output non-uniformity as described above,

(Equation 1)

(Equation 2) Is disclosed in the literature. However, in these methods, partial output non-uniformity may not be detected when adjacently appearing, or conversely, it may be determined that the output is within the allowable range but outside the allowable range. For example, FIG.
In the case where the partial output non-uniformity is continuous on the high output side as in the example shown in (a), according to the above equation (1), even when the output should finally fall outside the allowable range, However, there is a problem that it is not determined to be out of tolerance. Also, as in the example shown in FIG. 3 (b), when the high output and the low output are continuous, even if the output should finally fall within the allowable range when viewed from the peripheral average value, According to equation (2), there is a problem that it is determined to be out of tolerance. The present invention has been made in view of the above circumstances, and an object thereof is to solve the above-described problems in the conventional technology, to measure partial output non-uniformity automatically and efficiently, An object of the present invention is to provide an output non-uniformity measurement method that can be performed with high accuracy.

[0004]

SUMMARY OF THE INVENTION It is an object of the present invention to provide an image reading apparatus which irradiates a document with light, photoelectrically converts the reflected light with a light receiving element and reads the document. A method of reading a pattern having a uniform density of light by the light receiving element and measuring output non-uniformity from a difference in output voltage, wherein output voltages of all pixels output from the light receiving element are divided into n pixels. Measuring the output non-uniformity from the maximum value and the minimum value for each of the n pixels, or the average value of the (n−2) pixels excluding the maximum value and the minimum value and the maximum value and the minimum value. Achieved by the characteristic output non-uniformity measurement method.

[0005]

In the first output non-uniformity measuring method according to the present invention, the evaluation value is determined by targeting the n pixels and setting the denominator at the time of evaluation to the minimum value in the output of the n pixels. Is large, and large irregularities in the output signal are easily detected here, and the effect that the detection efficiency is improved can be obtained. Further, in the second output non-uniformity measuring method according to the present invention, the denominator at the time of evaluation is excluded from the maximum value and the minimum value in the output of the n pixels, so that the n pixels are similarly targeted ( By setting n-2), a more reliable evaluation value can be obtained. The value of n is preferably about 3 ≦ n ≦ 10.

[0006]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 4 shows an image reading apparatus (main configuration is the same as that of FIG. 1) according to an embodiment of the present invention.
3 shows a circuit configuration of a measurement unit that detects and determines partial non-uniformity in output. Here, it is assumed that the result of reading a document with uniform density over the entire surface by the image sensor 4 in FIG. 1 is a result as shown in FIG. In FIG. 4, reference numeral 11 denotes a CCD 1 constituting the image sensor 4.
2, which generates a basic clock by a crystal oscillator and divides and delays a reference clock to generate a plurality of clocks for driving the CCD. Further, a clock for driving the CCD is amplified and supplied to the CCD 12, and at the same time, a driving clock is supplied to the A / D converter and the image data memory. Also,
The analog image data from the CCD 12 is also amplified.

Reference numeral 13 denotes an I / O unit, which comprises a parallel processing unit and a serial processing unit. The parallel processing unit operates in accordance with an instruction from the CPU unit 14 to execute the A / D conversion unit 1
5, sending and receiving control signals between the bus switching unit 17 and the image data memory 16; The serial processing unit transmits and receives data and transmits and receives commands to and from a general control unit (not shown) according to a command from the CPU unit 14. Reference numeral 14 denotes the above-described CPU unit;
It is composed of a bit CPU, a ROM for storing programs, a working RAM for the CPU, and the like. In the ROM for storing the program, an adjustment method program, a communication program with the overall control unit, a control program of the parallel processing unit in the I / O unit 13, and the like are fixed. In the work RAM of the CPU, the progress and the parameters processed by the program fixed in the program storage ROM are stored by the CPU.

Reference numeral 15 denotes an A / D converter, which has a function of converting image data from the CCD 12 from analog to digital and transmitting digital data to the image data memory 16. The image data memory 16 stores CCD digital image data for each pixel. Reference numeral 17 denotes a bus switching unit, which is controlled by the parallel processing unit in the I / O unit 13 described above.
The image data memory 16 has a function of switching between the CPU unit 14 and the A / D converter 15 for the right of selection. Next, the operation of the present embodiment configured as described above will be described. The CPU unit 14 switches the bus switching unit 17 to the A / D conversion unit 15 for the I / O unit 13. An analog image signal from the CCD 12 is digitized by an A / D converter 15 and is converted to an image data memory 16.
Transferred to

The completion of data transfer to the image data memory 16 is notified to the CPU unit 14 via the I / O unit 13. Next, the CPU unit 14 determines the CP in the CPU unit 14.
While using the U work RAM, the adjustment method program in the CPU unit 14 is executed, and a digitized image in the image data memory 16 is read out during the execution process. The image data and the result processed by the adjustment method program are sent to the overall control unit by the CPU via the serial processing unit in the I / O unit 13. Since there are a plurality of adjustment method programs fixed in the program storage ROM in the CPU unit 14, the command sent from the control unit is
The decoding is performed in the U section 14 to determine which adjustment method is to be adopted and executed. Next, details of the measuring operation using the measuring unit shown in FIG. 4 will be described. First, the image sensor 4 reads the original 1 having a uniform density over the entire surface, amplifies a signal obtained by converting an optical signal into an analog electric signal, and amplifies the signal.
Send to 5.

The A / D converter 15 converts the analog electric signal that has been amplified and sent to a digital electric signal, and converts this signal as image data into the image data memory 1.
6 is stored. Next, the CPU reads the image data and the strict data from the image data memory 16 and the ROM of the CPU unit 14, compares the two data, and determines whether the partial output non-uniformity is within the allowable range. to decide. Specifically, first, all the pixels are divided into n pixels, and the change rate, the maximum value, and the minimum value for each n pixel are obtained. The above change rate is, for example,

(Equation 3) Is calculated by Since the minimum value of the output is used as the denominator in the equation (3), the presence or absence of extreme unevenness can be determined here.

If the result of the above calculation is out of the allowable range of the change rate, the output average value of (n-2) pixels excluding the maximum value and the minimum value of the corresponding n pixels is obtained.

(Equation 4) About the concave part,

(Equation 5) , The partial output non-uniformity is calculated again. The above-described two-stage output non-uniformity determination is performed by first determining the presence / absence of extreme unevenness according to Expression (3) using the minimum value of the output as the denominator. It is possible to judge that the non-uniformity of the output is small as a whole, and it is shown that a more detailed calculation is performed only when there is a corresponding one.

That is, according to the above-described embodiment, it is possible to obtain the effect that the measurement of the partial non-uniformity of the output can be automatically and efficiently performed with high accuracy. It should be noted that the above embodiment is an example of the present invention, and it is needless to say that the present invention is not limited to this. For example, the above formulas (3) to (5) are not limited to the above formulas, and other formulas (for example, Mitsuo Oshima, "How to select and use an image sensor" (Nikkan Kogyo Shimbun, Inc., 1960) Monthly publications) (see page 88) may be applied.

[0013]

As described above in detail, according to the present invention, the output nonuniformity measurement which can automatically and efficiently perform the partial output nonuniformity measurement can be performed with high accuracy. This has a remarkable effect that the method can be realized.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing a configuration example of a main part of an image reading device using a CCD as an image sensor.

FIG. 2 is a diagram illustrating an example of an output signal of an image sensor.

FIG. 3 is a detailed diagram illustrating an example of an output signal of an image sensor in which a problem may occur in a conventional output nonuniformity measurement method.

FIG. 4 is a diagram illustrating a configuration example of an output non-uniformity measurement unit in an image reading device using a CCD as an image sensor.

[Explanation of symbols]

1: original, 2: illumination, 3: lens, 4: image sensor, 11: CCD driver, 12: CCD, 13: I
/ O section, 14: CPU section, 15: A / D conversion section, 16:
Image data memory, 17: bus switching unit.

──────────────────────────────────────────────────続 き Continuation of front page (56) References JP-A-4-1199071 (JP, A) JP-A-62-181675 (JP, A) JP-A-4-114572 (JP, A) JP-A-2- 53375 (JP, A) JP-A-6-78147 (JP, A) JP-A-2-143678 (JP, A) JP-A-63-171068 (JP, U) (58) Fields investigated (Int. Cl. ⁷ , DB name) H04N 1/40-1/409 H04N 1/46 H04N 1/60

Claims (2)

(57) [Claims] An image reading apparatus for irradiating an original with light, photoelectrically converting the reflected light with a light receiving element and reading the original, wherein a pattern having a uniform density over the entire surface provided on the original placing surface is formed by the light receiving element. To measure the output non-uniformity from the output voltage difference ,
The output voltages of all the pixels output from the light receiving element are divided for every n pixels, and 、 (maximum value or minimum value of n pixels− (n−2) pixels
Mean value)} / ((n-2 ) output nonuniform resistance meter measuring method, characterized in that the average value of the pixel), for measuring the non-uniformity of the output. 2. The measurement of the non-uniformity of the output is performed as follows: ((the maximum value of n pixels−the average value of (n−2) pixels )) /
((N-2) average value of the pixel) is calculated based on, also, the entire
For the concave portion projecting below the average value of the output, {(minimum value of n pixels−average value of (n−2) pixels)} /
Output nonuniform resistance meter measuring method according to claim 1 Symbol placement and calculates based on ((n-2) average value of the pixel).