JPS62219185A - Image input device - Google Patents

Abstract

PURPOSE:To certainly perform the correction of variable density uneveness without offering a special correcting sample, by calculating correction factors for an offset and a gain, etc., by using a well known or an optional black and white correcting sample, and correcting a real video signal based on a calculated result. CONSTITUTION:The titled device is equipped with a photoelectric transducer 23 which performs the photoelectric conversion of a one-dimensional or a two-dimensional optical image on an image-forming lens 21 and an image-forming picture, and a storing means 29 which stores a digital signal obtained by A/D- converting a video signal from the photoelectric transducer 23. And an arithmetic means 30-1 image-picks up a correcting sample 26 consisting of the well known black and white pattern connected to the output side of the storing means 29, and calculates the correction factor for the offset and the gain from a difference due to the sample positions of the signal levels of a white and a black at the well known position in the image. In the actual image pickup time of a sample, a variable density correction circuit 10 performs the correction of the variable density uneveness for the video signal from the photoelectric transducer 23 based on the correction factor.

Description

[Detailed Description of the Invention] [Summary] The present invention relates to an image input device equipped with a correction circuit for performing offset correction and gain correction in order to correct non-uniformity of signals caused by uneven lighting, etc. .

The present invention images a calibration sample consisting of a known black and white pattern, calculates the density unevenness of the optical system from the difference in white or black signal labels at known positions in the image depending on the position of the sample, and then performs the actual sample imaging. Sometimes, based on the density unevenness calculation result, a density correction circuit is provided for correcting the actual video signal from the photoelectric conversion element and inputting the image. Furthermore, a correction control circuit is provided which repeatedly executes such correction until the positional variations in the white level and black level are eliminated. Furthermore, a calibration sample consisting of an arbitrary black and white pattern is imaged, and a peak detector is used to detect the maximum value of the video signal corresponding to the white pattern in the image and the minimum value of the video signal corresponding to the black pattern. The outputs of the detection circuit and the extreme value detection circuit are used to calculate the uneven density of the optical system from variations in the white level and black level depending on the position in the image, and when an actual sample video is used, the image signal is calculated based on the uneven density calculation results. The device is equipped with a shading correction circuit that corrects.

By using the present invention, it is possible to obtain an image signal without shading, and the corrected image signal can be used to accurately perform subsequent image processing. Moreover, by using the present invention, there is no need to present a special calibration sample to the device, and a standard imaging target can be used to
This has the effect that the correction can be performed reliably.

[Industrial application field]

The present invention relates to an image input device that inputs a large screen, and more particularly to a calibration method for an image input device that can perform offset correction and gain correction on an image signal from an image sensor in order to make a target screen uniform.

[Traditional technique]

With the development of large-scale integration technology, it is now possible to transmit high-quality images by performing large-scale image processing using computers, or to transmit image data to remote locations and play it back on the receiving side. Takatsuki-enabled devices are being put into practical use using recognition technology. When inputting an image to a frame memory, it has become extremely easy to increase the capacity of the frame memory, but when inputting a large screen, there is uneven illumination at the image input section, and the image is normally uniform. However, when the data is played back, unevenness may occur. This is because if the signal from the image sensor is input directly to the frame memory, the center of the imaging lens will be bright and the surroundings will be dark due to lens shading and uneven illumination.

In an input device that directly inputs the signal from the image sensor to the frame memory, for example, if two adjacent pixels of the target image capture a black and white lattice pattern, each consisting of white and black, the X with y constant
Originally, the imaging signal for the image has a waveform that repeats maximum and minimum gradation, and the envelope line has a constant height waveform. However, due to lens shading and illumination unevenness, a waveform in which the envelope of the imaging signal has a maximum value at the center is stored in the frame memory. If subsequent image processing is performed using an imaging signal containing such an error, there is a drawback that correct image processing cannot be performed.

Conventionally, as a method to correct illumination unevenness, a white level signal obtained by imaging a white object is stored in a white level memory.
There has been a method of correcting a subsequently inputted image signal by a DC offset amount using a white level signal output from a white level memory. However, such a correction method that uses only the white level has the disadvantage that although it can correct the DC offset, it cannot correct the gain, and therefore cannot completely correct unevenness in the amount of illumination. Ta.

In addition, conventionally, there is a correction method that uses white level and black level memories respectively for white level and black level, but this method has the disadvantage that it is necessary to image black and white samples and black samples respectively. had.

[Problem that the invention seeks to solve]

In order to eliminate such conventional drawbacks and correct non-uniformity of imaging signals due to uneven illumination, etc., the present invention calculates correction coefficients such as offset and gain using known or arbitrary black and white calibration samples. The present invention also provides an image input device that corrects an actual video signal based on the calculation result when inputting one image.

[Means for resolving issues]

According to the present invention, the above object includes an imaging lens, a photoelectric conversion element (23) that photoelectrically converts a one-dimensional or two-dimensional optical image on an imaging surface, and a video signal from the photoelectric conversion element that converts the image signal into an A/
A storage means (29) for storing a digital signal obtained by D conversion; and a calibration sample connected to the output side of the storage means (29), which images a calibration sample consisting of a known black and white pattern, and stores the white at a known position in the image. and a calculation means (30-1) for calculating correction coefficients for offset and gain from the difference in the signal level of each of black and black depending on the position of the sample; This is achieved by providing an image input device characterized in that it is equipped with a shading correction circuit (1o) that corrects shading unevenness.

[For production]

Image a calibration sample consisting of a known black and white pattern,
The density unevenness of the optical system is calculated from the difference in the white and black signal levels at known positions in the image depending on the position of the sample, and when actually capturing the sample, the actual video signal is corrected based on the above density unevenness calculation results. I try to do that.

Further, this correction is repeated until there are no variations in the white level and black level depending on the position.

Further, an extreme value detection circuit is provided which images a calibration sample consisting of an arbitrary black and white pattern and detects the maximum value of the video signal corresponding to the white pattern in the image and the minimum value of the video signal corresponding to the black pattern, Using this, the uneven density of the optical system is calculated from variations in the white level and black level depending on the position in the image, and when actually capturing a sample, the actual video signal is corrected based on the results of calculating the uneven density. .

〔Example〕

Next, embodiments of the present invention will be described with reference to the drawings.

FIG. 2 shows an embodiment of an imaging camera as an image input device. ta image object 20 is imaged by the imaging lens 21, and the one-dimensional image sensor 23 relative to the X direction is moved on the imaging plane 22 in the y direction perpendicular to the main scanning direction by a moving mechanism (not shown). A two-dimensional target image is obtained. Using such an imaging camera 24, the signal from the one-dimensional imaging device 23, that is, the analog grayscale value of each pixel of the image, is converted into a digital value by an A/D converter. If the digital signal is input as is into the frame memory, a two-dimensional image in which the center is bright and the periphery is dark, as shown in FIG. 3, is usually obtained when a white-only image is used as the object. This phenomenon occurs especially when the image is on a very large screen.

In other words, if the gray level value at the pixel coordinates (x, y) of the target image is expressed by the voltage value V (x, y), then for white, V
(x, y) must be constant, but V(x, y) is high in the center of the image and V(x.

y) will be lower. This is the imaging lens 2 of the imaging camera 24.
1 due to shading and illumination unevenness, and originally a uniform signal V (x, y) must be obtained. Therefore, in order to correct the non-uniformity of the imaging signal due to uneven illumination, etc., the present invention provides an imaging signal V from the -dimensional imaging element 23.
Offset 1-correction and gain correction are performed on (x, y).

FIG. 1 is a block diagram of the configuration of an image input device according to the present invention. The image input device of the present invention includes an imaging lens 21, a photoelectric conversion system that photoelectrically converts a one-dimensional or two-dimensional optical image on an imaging surface, and a video signal from the photoelectric conversion element to a next-stage processing circuit. Consists of a correction circuit for output. Then, in order to correct the uneven density of the input video signal, correction coefficients such as offset and gain are calculated using the known black and white calibration sample 26, and the video signal is adjusted based on the calculation results when inputting the image. This is to perform correction.

In the present invention, in order to correct illumination unevenness, first, a calibration sample 26 consisting of a known black and white pattern is imaged by the imaging lens 21 as an imaging target, and then the -dimensional imaging element 2
The white level signal W (x, y) and black level signal B (x, y) obtained from step 3 are converted into digital signals by the A/D converter 28, bypassing the correction circuit 27 inside the shade correction circuit 10. , are directly input to the frame memory 29. For example, in the calibration sample 26, if any adjacent pixels are alternately black and white as shown in FIG. The gray level signal of the image becomes a signal in which the black level and the white level appear alternately as shown in FIG. Here, it is assumed that the white level signal has the highest amplitude, the black level signal has the smallest amplitude, and intermediate colors ranging from black to white have amplitudes between them.

As shown in Figure 5, the black and white level is a waveform whose amplitude increases and decreases, but if the screen is large and there is uneven lighting or lens shading, even if the white level is the same, the white The level signal W(x, y) has various amplitude values in the X direction, and reaches the highest white level Wmax at the center of the screen. Similarly, the black level B (x, y) is higher at the center of the screen and lower toward the left and right boundaries. In this case, the amplitude value of the lowest black level in the screen is defined as B min.

In this way, the signal on the first line in an image in which black and white levels appear alternately as shown in Figure 4 becomes a signal in which black and white levels appear alternately as shown in Figure 5. It is sufficient that the shape of the black and white pattern is known as the calibration sample instead of the pattern. That is, any calibration sample may be used as long as it is known where white and black are located in the addresses in the frame memory 29. The white level and black level digital signals of such a known calibration pattern are stored in the frame memory 29.
The signal is read out from the gradation correction circuit 10 and input to the arithmetic circuit 30-1 of the grayscale correction circuit 10. The arithmetic circuit 30-1 detects the lowest black level Bll1n and the highest white level Wmax on the screen of the black and white pattern output from the frame memory 29. In other words, in the calibration sample shown in Fig. 5, when X is changed for scanning on the l line, the white level signal W
(x, y) is at the highest level in the center of the screen, and this value is detected as Wma. Also, regarding the black level signal B (x, y), when changing X, the level B (x
, y) becomes B min. This minimum black level B
min and the highest white level Wma, the following (offset shown in equation 11) is applied to each pixel value in each l row where β of the calibration sample shown in FIG. A value F (x, y) and a gain value G (x, y) are calculated.

F (x, )') = B (x, y) −B
winG (x, y) = −L Hiroshi−L−′/(X
・So---(1) Offset value F (x, y) and gain value G (x
, y) are output from the arithmetic circuit 30 and stored in the offset memory 31 and gain memory 32 inside the gray scale correction circuit 10.

Then, when the calibration sample 26 is removed, the actual imaging target 20 is imaged by the imaging lens 21, and the analog video signal input via the -dimensional image sensor 23 is input to the correction circuit 27, the offset The offset F (x, y) and gain value G (x, y) are transferred from the memory 31 and gain memory 32 to the D/A converter 33 respectively.
and 34 to the correction circuit 27. That is, during actual sample imaging, the respective outputs from the offset memory 31 and gain memory 32 are transferred to the D/A converter 33. and 34, it is converted into an analog signal and input to the correction circuit 27, and the actual video signal is corrected according to the following equation (2).

V'= G (x, y) x (V (x, y) - F (x, y)
)...(2) V' obtained by equation (2) is the offset value F (x, y) obtained according to equation (1) and gain value G (x.

This is a video signal corrected using y), in which variations in white level and black level due to position have been removed based on the above correction. In addition, after calculating the correction coefficient obtained by the formula +1), in order to further improve the accuracy of correction, the correction control circuit 30-2 images the calibration sample 26 again using this coefficient, and calculates a precise correction coefficient. make it possible to

In this way, not only the correction is performed once, but also the correction control circuit 3
By repeating the correction several times using 0-2,
The actually inputted video signal is used in the correction circuit 27 to obtain an even, high-quality image, and is stored in the frame memory 29 via the A/D converter 28. That is, by using the above-described method, it is possible to reliably measure the density unevenness simply by presenting the calibration sample 26 to the apparatus.

In the first embodiment described above, the positional information regarding the position of the black pattern and the position of the white pattern is already known, and based on the positional information, equations (1) and (2) are
Variations in black and white levels were calculated from the formula, and the actual video signal was corrected based on the calculation results. In the second embodiment described below, even if the position information of the white level signal and the black level signal is not obtained and the actual imaging target 20 is arbitrarily given, the local maximum value W of the white level from the target sample (xn, y, ,) and the minimum black level value B(Xn.

yl, ) using the extreme value detection circuit 35 shown in the block diagram of FIG.
It can be calculated using 0-1.

Here, the configuration block of FIG. 6 is almost the same as the configuration block of FIG. 1, but the extreme value detection circuit 35 is inserted between the frame memory 29 and the arithmetic circuit 30-1. . For example, a calibration sample consisting of an arbitrary black and white pattern as shown in FIG. The signal minimum value is detected by the extreme value detection circuit 35.
Detect using. For example, when scanning the center of the numbers 1 to 8 in the first row in the calibration sample consisting of the black and white pattern shown in FIG. 7, the output of the extreme value detection circuit 35 will be the maximum value of the black and white pattern waveform shown in FIG. W(x, 1.yn)
and the minimum value B (xn, yn). Based on the signal obtained from the extreme value detection circuit 35, the variation in white level and black level depending on the position in the image is determined by the following equation. That is, the offset value F (X n+ )I n
> and gain value G (X 11+ )! n) is determined by the following formula.

F (xn+ yn)=B (xn+ 3'n)-
BminG(X, 1.yn)'=t-L-i(λ1.I, tan) Here, Bmin is the lowest minimum value and Wmax is the highest maximum value.

The offset value and gain value thus determined are similarly stored in the offset memory 31 and gain memory 32, respectively. Then, the actual video signals are inputted to the correction circuit 27 via the D/A converters 33 and 34, respectively, and the actual imaged object 20 is imaged by the imaging lens 21 and inputted via the one-dimensional image sensor 23. For (2
) By obtaining the correction signal v' according to the equation (2), it is possible to reliably correct unevenness in density.

〔Effect of the invention〕

As explained above, the present invention can calculate correction coefficients for offset and gain by using known or unknown black and white calibration samples, and corrects unevenness in density of video signals based on the calculation results for actual image input. The effect is that it can be done.

[Brief explanation of drawings]

FIG. 1 is a block diagram of the configuration of the image input device of the present invention. 21! Figure 3 is a diagram showing the two-dimensional image obtained from the 1rlJ image element without correction, Figure 4 is a pattern diagram of a known calibration sample, and Figure 5 is a diagram of the configuration of the imaging device. Figure 6 is a waveform diagram showing non-uniform imaging signals when correcting the black and white lenses of the calibration sample. A block diagram of the configuration of the image input device of the present invention; FIG. 7 is a pattern diagram of an arbitrary calibration sample from which the maximum value of the white level and the minimum value of the black level can be obtained using the circuit of FIG. 6; FIG. 8 is a waveform diagram of a video signal obtained when scanning the center of the numbers 1 to 8 in the first row of FIG. 7. FIG. 20... Imaging target, 21... Imaging lens, 22... Imaging surface, 23... -dimensional imaging element, 24... Imaging camera, 25... Movement mechanism, 26... Calibration sample, 27... Correction circuit, 2-8... A/D converter, 29... Frame memory, 30-1... Arithmetic circuit, 30-2... Correction control circuit 31...・Offset memory, 32...Memory, 33.34...D/A converter, Patent applicant: Fujitsu Ltd. 1. OJ kotogo father's pain 2. illustrative self (correct) 1. 31 ゛ Urero Kosui 7c, 1. Figure 1 shows the number 3 of the 3 m. 1Σ
Show 1 picture book 51!1

Claims (1)

[Claims] 1) A photoelectric conversion element (23) that photoelectrically converts a one-dimensional or two-dimensional optical image on an imaging lens and an imaging surface, and A/D converting a video signal from the photoelectric conversion element. storage means (29) for storing the digital signals obtained by the image processing; calculation means (30-1) for calculating correction coefficients for offset and gain from the difference in signal level depending on the position of the sample; An image input device comprising: a shading correction circuit (10) that corrects shading unevenness. 2) A correction control circuit (30
-2) The image input device according to claim 1, characterized by comprising: -2). 3) Using the output of an extreme value detection circuit that images a calibration sample consisting of an arbitrary black and white pattern and detects the maximum value of the video signal corresponding to the white pattern in the image and the minimum value of the video signal corresponding to the black pattern. Claim 1, wherein the calculation means calculates the correction coefficient, and the density correction circuit corrects density unevenness with respect to a video signal from a photoelectric conversion element during actual sample imaging. The image input device described.