JPH06261346A - Cutoff measurement method for crt device - Google Patents

Abstract

PURPOSE:To obtain a highly precise cutoff measurement value from which random noise and a quantized error are removed by analog/digital-converting a video signal which image-picks up the fluorescent surface of a CRT device, storing it into an image memory and adding the content of the image memory. CONSTITUTION:The cutoff measurement method of the CRT device 106 includes a process for image-picking up the fluorescent surface of the CRT device 106 where a raster image is displayed by an image pickup device 101, a process for converting the video signal outputted from the image pickup device 101 into a digital signal by an analog/digital converter 102 for respective and prescribed image elements, a process for storing signals digitalized for the respective image elements into the image memory 103, a process for adding the content of the image memory 103 in an adder 104 and obtaining the signals and a process for measuring the cutoff deviation quantity of the CRT device 106 based on the sum of the signals.

Description

Detailed Description of the Invention

[0001]

The present invention relates to a CRT (Cathode Ray).
Tube, cathode ray tube, or picture tube), and more particularly to a method for measuring the fluorescent screen luminance in the cutoff adjustment of a television receiver or a CRT display device.

[0002]

SUMMARY OF THE INVENTION One of the important manufacturing processes for television receivers and CRT display devices (hereinafter abbreviated as CRT devices)
One is the cutoff adjustment process. This cut-off adjustment is to adjust the bias voltage applied to the CRT.
The bias voltage between the first grid of the CRT and the cathode is gradually increased to adjust the bias voltage to a value at which electrons are not emitted from the cathode. The determination that the emission of electrons from the cathode of the CRT is stopped is actually made by stopping the emission of light from the CRT phosphor screen. Therefore, there is a need for a technique for measuring a light amount called a cutoff shift amount, which has an extremely low brightness.

According to the present invention, a video signal of a fluorescent screen of a CRT device is converted from an analog signal to a digital signal and stored in an image memory, and then the contents of the image memory are added.
It is a cutoff measurement method for a CRT device capable of obtaining a highly accurate cutoff measurement value from which random noise and quantization error are removed.

[0004]

2. Description of the Related Art The cutoff adjustment of a television receiver or a CRT display device is a work for adjusting a bias voltage so that the light emission on the CRT phosphor screen is not exactly visible, and therefore a technique for measuring extremely low brightness is indispensable. Yes,
It was difficult to make a measuring instrument. Therefore, conventionally, the cutoff adjustment has been performed by an operator exclusively by visually observing the fluorescent screen of the CRT device to determine the cutoff.

Further, the fluorescent screen of the CRT device is imaged by an image pickup device, the image signal thus picked up is converted into a digital value by an analog / digital converter, and from this value C
Conventionally, a method of measuring the amount of light emitted from the RT has been tried. However, the measuring method using such a digital light quantity measuring device is limited to the case where the fluorescent screen luminance of the CRT is high, for example, when the intensities of the three primary colors of the color CRT are made uniform, or the color unevenness of the color CRT is measured, and it is low. S / N for brightness
It was not available due to the extremely low ratio.

That is, until the emission of the CRT phosphor screen becomes a digital measurement value, the phosphor screen emission, the image pickup device, the video signal conversion circuit, the video signal transmission line, the video signal amplification circuit, and the analog / digital converter are complicated. In order to reduce the S / N ratio by passing through the process, and in particular, to transmit weak light near the low-luminance imaging limit between the fluorescent screen and the image sensor, the measurement by the digital light meter is Enough S
/ N ratio cannot be obtained.

[0007]

However, the conventional cutoff adjustment by the operator's visual observation has a problem in that it is not possible to perform highly accurate adjustment without variations, which is an obstacle to uniform product manufacturing. In addition, the conventional digital light quantity measuring device has a problem that the light quantity of extremely low brightness, which is the target of the cutoff adjustment, is buried in noise and cannot be measured with a required accuracy. In view of the above-mentioned problems, an object of the present invention is to measure an extremely low CRT brightness with high accuracy, and
It is an object of the present invention to provide a method for measuring a cutoff of a T device.

[0008]

In order to achieve the above object, the present invention has the following constitution. That is, according to the present invention, in a cutoff measuring method for a CRT device, a step of capturing an image of a fluorescent screen of a CRT device displaying a raster image with an image capturing device, and a video signal output from the image capturing device for each predetermined pixel. A step of converting into a digital signal by an analog / digital converter, a step of storing a signal digitized for each pixel in an image memory, a step of adding the contents of the image memory to obtain a sum of the signals, And a step of measuring a cutoff deviation amount of the CRT device based on the sum, the cutoff measuring method of the CRT device.

[0009]

According to the method of cumulative addition in the cut-off measuring method of the CRT device according to the present invention, it is possible to obtain a video signal of a CRT fluorescent screen having a very weak brightness near the low brightness imaging limit of the imaging device. The average value of the measurement target can be calculated with extremely high accuracy from a signal having a low signal level and an extremely poor S / N ratio. That is, when an analog signal containing random noise is digitized and the N total sums are calculated, the total sum = N x (original average value) + N x (noise average value)
+ Σ (quantization error).

Here, if N is a sufficiently large value, the quantization error Σ for digitization cancels each other out of positive and negative and becomes almost 0, and N × (average value of noise) is a value peculiar to the measurement system ( Suppose it is B). As a result, the above equation is simplified to the following formula: total sum = N × (original average value) + B. In this way, it is possible to measure the cutoff deviation amount of the CRT device with high accuracy at low brightness near the low brightness imaging limit of the imaging device.

[0011]

Embodiments of the present invention will now be described in detail with reference to the drawings. FIG. 1 is a block diagram of a measuring device used in a cutoff measuring method for a CRT device according to the present invention.
In the figure, 101 is an imaging device, and 102 is an analog /
Reference numeral 103 is a digital converter, 103 is an image memory, 104 is an adder, 105 is a determination unit, 106 is a television receiver which is the device under test, and 110 is a light shielding hood.

External light is blocked between the television receiver 106 to be measured and the image pickup device 101, and the image pickup device 1 only emits light from the CRT phosphor screen of the television receiver 106 to be measured.
A light shielding hood 110 is provided so as to enter 01. As the image pickup apparatus 101, an apparatus equivalent to the image pickup apparatus used for conventional color balance and color unevenness measurement is used.

It is well known that the analog / digital converter 102 determines the quantization unit in consideration of the dynamic range of the cutoff deviation amount measuring range and the noise level included in the output signal of the image pickup device 101. But
Even if the quantization unit is unnecessarily reduced and the converted digital value is increased, the accuracy cannot be improved because the original analog value has a low S / N ratio.

The image memory 103 has the same number of storage areas as the predetermined number of pixels, and stores the digitized signal representing the luminance on the CRT for each pixel. The bit widths of these storage areas may be selected so as not to be smaller than the output bit width of the analog-digital converter 102.

The adder 104 cumulatively adds the luminance information for each pixel stored in the image memory 103 to obtain a total sum.
The data width of the adder 104 is calculated in consideration of the number of effective digits of the data stored in the image memory 103 and the number of pixels to be added.
It is advisable to provide a bit width that does not cause loss of digits, or to devise an arithmetic means such that an appropriate partial sum is obtained.

The determination unit 105 determines the cutoff deviation amount based on the total sum obtained by the adder 104. This determination will be described in detail later.

Next, the cutoff measuring method of the present invention will be described in the order of steps. First, the measured television receiver 10
A raster image is displayed at 6. Normally, a raster image is displayed by an operation such as pulling out a service chip provided in the television receiver.

Next, the measured television receiver 1 is measured.
The raster image displayed on the image capturing device 101.
To image. Since the raster image captured at this time has extremely low brightness, the video signal 201 output from the imaging device 101 is extremely weak and has a relatively high noise level.

Next, the analog video signal 201 imaged and output by the image pickup device 101 is converted into a digital value by the analog / digital converter 102,
It becomes the digital image signal 202 and is stored in the image memory 103. The analog / digital conversion of the image signal is performed for each predetermined pixel, and the image memory 103 is performed for each pixel.
Stored in.

Then, the adder 104 cumulatively adds the sums of the image signals representing the brightness of the raster image stored in the image memory 103 for each pixel to obtain the sum. Next, the measured value of the cutoff deviation amount is calculated from the sum of the addition results.

According to the cumulative addition method in the cutoff measuring method for the CRT device according to the present invention, the random noise included in each digital data and the quantization error generated by the analog / digital converter 102 are averaged. Can be eliminated. This will be described in detail with reference to the drawings.

FIG. 2 schematically shows the luminance data for each pixel stored in the image memory 103. In the figure, one cell represents the storage location of the image memory corresponding to one pixel, and the number in the cell represents the digitized luminance of that pixel. As described above, since the signal having a low signal level and an extremely poor S / N ratio contains analog-to-digital converted data, random noise is included.
Different values are stored for each.

However, the number of digital data stored in the image memory 103 is usually 200,000 (50
Since there is a number of about 0 (corresponding to 0 × 400 pixels), if addition and accumulation are performed by the adder 104, the effects of random noise and quantization error will always be almost the same value.
As described in the section of action.

Next, a method of determining the cutoff deviation amount will be described. FIG. 3 is a graph showing the amount of light emitted from the fluorescent screen of the television receiver on the horizontal axis and the addition result of the adder 104 on the vertical axis. In the figure, point A is a point where the light emission from the fluorescent screen of the television receiver has just disappeared, that is, a cutoff point. The value indicated by B is the random noise that has been added and accumulated. The determination unit 105 subtracts the value B from the addition result of the adder 104, and enables the amount of light emitted from the fluorescent screen of the television receiver to be measured to an extremely low luminance.

Although the preferred embodiment has been described above, this is not meant to limit the invention. For example, the correspondence between the image memory and the pixels does not necessarily have to be one-to-one, and the analog video signal sampled every several pixels may be digitized and stored in the pixel memory. Further, it is not necessary to add all the stored pixels, and it is possible to obtain the sum representative of the brightness by performing the addition for some areas representing the brightness on the screen.

[0026]

As described above, according to the present invention,
Since it is possible to automatically perform the inspection and adjustment of the cutoff deviation of the television receiver, which has been conventionally performed by visual inspection, it is possible to save labor in the production process and improve working conditions. The error in the cutoff adjustment of the television receiver is extremely small, and the quality of the product can be improved.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of a device of a cutoff measuring method for a CRT device according to the present invention.

FIG. 2 is a schematic diagram of brightness data stored in an image memory.

FIG. 3 is a graph showing the relationship between the amount of light emitted from the phosphor screen and the addition result.

[Explanation of symbols]

 101 Imaging Device 102 Analog-Digital Converter 103 Image Memory 104 Adder 105 Judgment Unit 106 Television Receiver Under Test 110 Light-Shielding Hood

Claims (1)

[Claims] 1. A method for measuring a cutoff of a CRT device, comprising: a step of capturing an image of a fluorescent screen of a CRT device displaying a raster image by an image capturing device; and an image signal output from the image capturing device is analogized for each predetermined pixel. / A step of converting into a digital signal by a digital converter, a step of storing a signal digitized for each pixel in an image memory, a step of adding contents of the image memory to obtain a sum of the signals, and a sum of the signals And a step of measuring a cutoff deviation amount of the CRT device based on the above.