JPH04269610A - Method for inspecting periodic pattern - Google Patents

Abstract

PURPOSE:To inspect the distribution of the transmittance of the periodic pattern of an object under inspection in high accuracy. CONSTITUTION:The images of transmitted light under the state, wherein an object under inspection is arranged between alight source and a camera, and the image of the light source in the state wherein the object under inspection is removed, are picked up with a camera 3. An offset part is subtracted with respect to the image signal from the camera 3. Then, the signal is amplified. The brightness data of the image of the transmitted light wherein the difference of gradation at the unequal parts of a periodic pattern and the brightness data of the image of the light source are obtained. Operations such as division and subtraction are performed between the brightness data of the image of the transmitted light and the brightness data of the image of the light source are performed. Thus, the influence of the partial sensitivity difference of the camera contained in the brightness data is removed.

Description

[Detailed description of the invention]

[Object of the invention]

0002

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a periodic pattern inspection method for inspecting the quality of an object to be inspected having a periodic pattern, such as a display device such as a color cathode ray tube or a liquid crystal matrix.

0003

2. Description of the Related Art In a display device such as a color cathode ray tube or a liquid crystal matrix, uniform transmission characteristics such as a shadow mask are required in order to display images with uniform display screen brightness. That is, a periodic pattern formed on a shadow mask or the like is required to have uniformity.

[0004] The uniformity of the periodic pattern is generally inspected visually, but the inspection accuracy is lacking and there are problems with reliability.

[0005] Therefore, for example, Japanese Patent Application Laid-Open No. 62-201335
As described in the above publication, an inspection method for automatically inspecting periodic patterns has been proposed. This involves placing an object to be inspected with a periodic pattern between it and the light source, and capturing a transmitted light image according to the periodic pattern with a camera, which is then separated into multiple pixels based on the image signal from the camera. The image data of each frame is obtained. By suppressing noise generated during the image data acquisition stage and extracting non-uniform parts of the periodic pattern, it is possible to automatically determine whether a product is good or bad based on the non-uniform parts in the image data. I have to.

[0006]

[Problems to be Solved by the Invention] However, in the above-mentioned inspection method, it is not possible to eliminate the influence of variations in local sensitivity differences between the image pickup elements of the camera, and variations in inspection accuracy tend to occur. Since the gradation difference in the obtained image data is extremely small, there is a problem in that the inspection accuracy cannot be improved.

[0007] The present invention has been made in view of these points, and it is possible to prevent variations in inspection accuracy and improve inspection accuracy by eliminating the influence of variations in local sensitivity differences of cameras. It is an object of the present invention to provide a method for inspecting periodic patterns that can be performed.

[Configuration of the invention]

[0009]

[Means for Solving the Problems] The present invention provides a transmitted light image corresponding to a periodic pattern when an object to be inspected having a periodic pattern is placed between it and a light source; A light source image is captured by each camera, and the offset is subtracted from the frame-by-frame image signal decomposed into a plurality of pixels from the camera, and then the offset is amplified to obtain the brightness data of the transmitted light image and the brightness of the light source image. Then, the transmittance distribution of the periodic pattern of the object to be inspected is inspected from the brightness data of the transmitted light image and the brightness data of the light source image.

0010

[Operation] In the present invention, the brightness data is obtained by subtracting an offset from the image signal obtained by capturing a transmitted light image corresponding to the periodic pattern of the object to be inspected using a camera, and then amplifying the image signal to determine the brightness data. Increase the step difference at non-uniform parts of the periodic pattern included in the data.

[0011] By performing arithmetic processing such as division and subtraction between the brightness data of the transmitted light image and the brightness data of the light source image, the partial sensitivity difference of the camera included in each brightness data is calculated. Eliminate the effects of

[0012] Therefore, the transmittance distribution of the periodic pattern of the object to be inspected can be inspected with high accuracy.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The structure of an embodiment of the present invention will be described below with reference to the drawings.

FIG. 2 shows the configuration of the optical system, where 1 is a light source;
A diffuser plate 2 that diffuses and transmits light is placed opposite the light source 1, and a camera 3 is placed opposite the diffuser plate 2. An inspection object 4 having a periodic pattern, such as a shadow mask of a cathode ray tube, is placed between the diffuser plate 2 and the camera 3. In the case of a shadow mask, a plurality of slits are formed in this inspection object 4, and the plurality of slits constitute a periodic pattern.

FIG. 1 shows the configuration of the inspection apparatus, and a camera 3 sequentially outputs image signals that are scanned in frame units that are divided into a plurality of pixels. A scanning synchronization signal is added to this image signal.

The camera 3 includes a synchronization signal separator 5 that separates the synchronization signal from the image signal output from the camera 3, an offset adjuster 6 that subtracts the offset of the image signal, and an amplifier 7 that amplifies the image signal. , and a synchronizing signal adder 8 for adding together the synchronizing signal separated by the synchronizing signal separator 5 to the image signal.

An image arithmetic unit 10 is connected to the synchronizing signal adder 8 via an AD converter 9 that converts analog image signals into digital ones. The image calculator 10 includes a first frame memory 11 that stores brightness data of a light source image;
The second frame memory 12 stores the brightness data of the transmitted light image, and the first frame memory 11
The second frame memory 12 has a function of dividing the brightness data stored in the second frame memory 12 by the brightness data stored in the second frame memory 12.

Further, an image signal from the camera 3 is directly input to the image calculator 10 via an AD converter 13.

Next, the operation of this embodiment will be explained.

An object to be inspected 4 is placed between the diffuser plate 2 and the camera 3.
A light source image is captured by the camera 3 without setting the light source.

The image signal from the camera 3 is, with the synchronization signal once separated, an offset amount subtracted and amplified, and then the synchronization signal is summed again and converted into digital brightness data to form an image. It is stored in the first frame memory 11 of the arithmetic unit 10.

The brightness data of the light source image stored in the first frame memory 11 of this image calculator 10 is shown in FIG. 3(a).
Shown below. The distribution is such that the center becomes brighter depending on the position of the light source 1.

Further, with the object to be inspected 4 set between the diffuser plate 2 and the camera 3, a transmitted light image corresponding to the periodic pattern of the object to be inspected 4 is captured by the camera 3.

The image signal from the camera 3 is once separated from the synchronization signal, the offset is subtracted and amplified, and then the synchronization signal is summed again and converted into digital brightness data to form an image. It is stored in the second frame memory 12 of the arithmetic unit 10.

Second frame memory 12 of image arithmetic unit 10
The brightness data of the transmitted light image stored in is shown in FIG. 3(b). Note that FIG. 3(b) shows the same frame of brightness data as shown in FIG. 3(a).

By the way, in each of the brightness data shown in FIGS. 3A and 3B, if there is a local sensitivity difference in the camera 3, an uneven waveform appears at the same location.

Furthermore, in the brightness data of the transmitted light image shown in FIG. 3(b), even if the periodic pattern of the object 4 to be inspected has non-uniform portions, this will appear as an uneven waveform. Furthermore, since the brightness data is obtained by subtracting the offset and then amplifying it, non-uniform areas appear as large uneven waveforms.

The image calculator 10 then divides the brightness data of the light source image stored in the first frame memory 11 by the brightness data of the transmitted light image stored in the second frame memory 12. By performing this calculation, the influence of the local sensitivity difference of the camera 3 included in each brightness data is removed, and the obtained brightness data is shown in Figure 3.
(c) Shown in (c).

The brightness data shown in FIG. 3(c) is expressed with the influence of local sensitivity differences of the camera 3 removed as described above, and also shows large irregularities in non-uniform areas of the periodic pattern. It is expressed as is as a waveform.

[0030] Therefore, since the influence of variations in local sensitivity differences of the camera 3 is removed and the step difference at non-uniform portions of the periodic pattern is increased, variations in inspection accuracy are prevented and inspection accuracy is improved. be able to.

[0031] When this inspection method is used to automatically determine whether the periodic pattern of the inspection object 4 is good or bad,
In the brightness data shown in Figure 3(c), non-uniform areas in the periodic pattern are represented as large uneven waveforms, so automatic determination of non-uniform areas can be easily performed and the accuracy of the judgment can be increased. can.

Note that FIG. 3(d) shows a comparison when the brightness data of the light source image is directly divided by the brightness data of the transmitted light image without performing offset and amplification processing on the image signal from the camera 3. As an example, it becomes stepwise and lacks precision. That is, if the brightness data of the light source image is divided by the amount of transmitted light without performing amplification processing on the image signal from the camera 3, stepwise data will be obtained. For example, the brightness is 400~
If you divide the data in the range of 500 by the brightness of 50 to 150, the answer will only take values in steps of 3 to 10, and the ideal solution curve will only take values in steps of 7. cannot fulfill its purpose.

[0033] Also, the image signal obtained from the camera 3 is
By converting the data into digital image data using the D converter 13 and storing it once in the memory of the image processor 10, the image processor 10 calculates the offset amount of the offset adjuster 6 and the increase rate of the amplifier 7 based on the image data. control. Thereby, it is possible to automatically deal with cases where the transmittance differs significantly depending on the object to be inspected 4.

Furthermore, a logarithmic amplifier that performs logarithmic conversion of the image signal may be used instead of the amplifier 7. In this case, not only it becomes possible to capture even more minute changes, but also the first frame memory Since the arithmetic processing between the brightness data of the light source image 11 and the brightness data of the transmitted light image stored in the second frame memory 12 can be performed by subtraction instead of division, processing can be performed in a short time.

[0035]

[Effects of the Invention] According to the present invention, brightness data is obtained by subtracting an offset from an image signal obtained by capturing a transmitted light image corresponding to a periodic pattern of an object to be inspected using a camera, and then amplifying the image signal. , the step difference at the non-uniform portion of the periodic pattern included in the brightness data is increased. By performing arithmetic processing such as division and subtraction between the brightness data of the transmitted light image and the brightness data of the light source image, the influence of local sensitivity differences of the camera included in each brightness data is eliminated. Remove. Therefore, the transmittance distribution of the periodic pattern of the object to be inspected can be inspected with high precision and without variation, and a highly reliable inspection method can be provided.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of the periodic pattern inspection method of the present invention.

FIG. 2 is a configuration diagram of an optical system.

FIG. 3 is an explanatory diagram of brightness distribution.

[Explanation of symbols]

1 Light source 3. Camera 4. Object to be inspected

Claims (1)

[Claims] Claim 1: A camera captures a transmitted light image according to the periodic pattern when an inspection object having a periodic pattern is placed between the light source and a light source image when the inspection object is removed. Then, after subtracting the offset from the frame-by-frame image signal decomposed into a plurality of pixels from the camera, it is amplified to obtain brightness data of the transmitted light image and brightness data of the light source image, and this transmitted light is A method for inspecting a periodic pattern, comprising inspecting a transmittance distribution of a periodic pattern of an object to be inspected from image brightness data and light source image brightness data.