JP3277384B2 - Image 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 image measuring method ,
In particular, the present invention relates to an image measuring method for measuring color unevenness of a solid-state imaging device equipped with a color filter.

[0002]

2. Description of the Related Art In a solid-state image pickup device equipped with a color filter, a characteristic color unevenness defect occurs in a process of manufacturing the color filter. Conventionally, no general method has been established for detecting this color unevenness defect with an image tester. This is because color unevenness is an unspecified pattern that is difficult to extract by general pattern recognition.

On the other hand, various methods are known as a filtering method using a low-pass filter for the purpose of band limitation and noise removal of an input signal of an image tester. These are roughly classified into convolution integration, moving average method, block division method, etc.

[0004]

However, the former convolution integration method has a problem that when the product-sum operation is realized on a general image tester, the processing time is required as the number of taps increases. Generally, it is desired to develop dedicated hardware, but there is a drawback that lacks versatility.

On the other hand, the latter block division method involves image distortion and compression of image data, and therefore requires careful design, but the number of times the multiplier is used is affected by the block size in terms of processing speed. Therefore, much faster processing than the former convolution method is possible.

[0006] The present invention was made in view of the above, the image measurement direction which enables realizing a process close to the determination of the human eye using the block division method capable of high-speed processing
The purpose is to provide the law .

[0007]

According to the present invention, there is provided an image measuring method for measuring color unevenness failure of a solid-state image pickup device provided with a color filter, comprising: If the number of divisions is 500 ± 100 KHz or 125 ± 25 KHz
And set based on the output signal of the solid-state image sensor.
Color caused by color filter using block division method
The unevenness is measured.

[0008]

The horizontal repetition frequency is set to 500 ± 100 KHz or 12 KHz.
By setting the frequency to 5 ± 25 KHz, the chroma signal of the imaging output of the solid-state imaging device can be converted to NT for a fine color unevenness pattern or shading-like color unevenness.
In addition to restricting the band to the horizontal / vertical resolution of the SC system, it is possible to restrict the high frequency range including the sense of resolution of the human color difference signal. As a result, it is possible to cause the image tester to perform processing close to the determination of the human eye.

[0009]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 2 is a block diagram showing one embodiment according to the present invention. In the figure, the charge-coupled device (CC
The CCD imager 1, which is a solid-state image sensor formed using D (Charge Coupled Device), is provided with a color filter (not shown) on its image sensing area. This CCD
The imaging output of the imager 1 is digitized by the A / D converter 2 and stored in the frame memory 3.

The CCD image tester 4 according to the present invention uses a block division method as a filtering method using a low-pass filter for the purpose of limiting the band of an input signal and removing noise, and is controlled by a controller 5 using a CPU. As a result, 1 stored in the frame memory 3
Detection (measurement) of color unevenness defect caused by the color filter is performed based on the image data of the frame.

By the way, since the human eye tends to significantly deteriorate the visual acuity (resolution) with respect to the color difference as compared with the luminance difference, the chroma signal is about 1% in the NTSC system.
The band is limited to around MHz. Thus, the upper limit of the number of block divisions corresponding to the low-pass filter of the image tester 4 can be suppressed to a band of 2 MHz by the Nyquist theorem. However, most color uneven patterns are macroscopic when viewed macroscopically, and it is easier to detect as a macro shape if the band that can be judged to be uneven by human eyes is more easily detected as a macro shape. The effect is also increased.

In order to examine the resolving ability of the human eye with respect to various color unevenness patterns of an image by the CCD imager 1 with a color filter, the bandwidth of the block division is set to 2M.
In this application, it is possible to suppress a band of 500 ± 100 KHz by gradually changing the frequency from Hz to around 100 KHz and evaluating an output image of a thin color unevenness pattern (local color unevenness) failure. Obtained by the inventor. In addition, a result is obtained that the band can be limited to around 125 ± 25 KHz with respect to shading-like color unevenness that occurs on the entire screen.

From this evaluation result, the number of block divisions in the horizontal direction that limits the band to the limit of human judgment can be determined.
That is, assuming that the frequency of the subcarrier is fsc, in the case of a CCD imager having a horizontal drive frequency of 4 fsc (= 14.3 MHz), 500. ±.
Since it is possible to suppress the band to 100 KHz, for example, the band limitation of 500 KHz (horizontal repetition frequency) is 1 MHz according to the Nyquist theorem, and the number of effective horizontal pixels is 768 bits.

## EQU1 ## From NH = 768 × 1 MHz / 14.3 MHz, 53 is obtained.

The number of block divisions NV in the vertical direction is
It can be obtained by multiplying by the aspect ratio (3/4). That is,

## EQU2 ## From NV = 53 × 3/4, the value is 40.

Therefore, in the case of a thin color unevenness pattern, the band can be limited to 500 ± 100 KHz. Therefore, as shown in FIG. In addition, by deciding so as to match the human criterion, the chroma signal of the imaging output of the CCD imager is limited to a band according to the horizontal / vertical resolution of the NTSC system, and the resolution for the color difference signal of the human It is possible to limit the high range including the feeling. As a result, it is possible to cause the image tester to perform processing close to the determination of the human eye.

On the other hand, since the band can be limited to about 125 ± 25 KHz for the shading-like color unevenness, the Nyquist frequency is set to 250 KH to suppress the band to, for example, 125 KHz (horizontal repetition frequency).
Assuming that z is the horizontal division number NH,

## EQU3 ## From NH = 768 × 0.25 MHz / 14.3 MHz, 13 is obtained.

The number of block divisions NV in the vertical direction is

## EQU4 ## From NV = 13 × 3/4, the value is 10.

Therefore, in the case of shading-like color unevenness, the band can be limited to 125 ± 25 KHz. For example, as shown in FIG.
By dividing the V into blocks and determining the number of block divisions theoretically and in accordance with the human criterion, it becomes possible to cause the image tester to perform processing close to human eye determination.

[0019]

As described above, according to the present invention,
Equipped with a color filter was of the solid-state imaging device color irregularity of the defective
At the time of the measurement, the chroma signal of the imaging output of the solid-state imaging device is converted into the horizontal / next-mode signal of the NTSC system by determining the number of horizontal block divisions of the color filter so as to match theoretically and human criteria. in addition to limiting the band conforming to the vertical resolution, the resolution sense of human color-difference signal is also included and it is possible to limit the high frequency, performs image measurement at close determination to the determination of the human eye This has the effect that it becomes possible.

[Brief description of the drawings]

FIG. 1 is a diagram showing an example of block division of a color filter. FIG. 1A shows a case corresponding to a thin color uneven pattern.
(B) shows a case corresponding to shading-like color unevenness.

FIG. 2 is a block diagram of one embodiment according to the present invention.

[Explanation of symbols]

 1 CCD imager 3 Frame memory 4 CCD image tester 5 Controller

Continuation of the front page (56) References JP-A-3-289798 (JP, A) JP-A-3-258092 (JP, A) JP-A-3-258091 (JP, A) JP-A-3-173292 (JP) JP-A-3-97075 (JP, A) JP-A-1-46393 (JP, A) JP-A-63-200278 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB (Name) H04N 17/02

Claims (2)

(57) [Claims] 1. An image measuring method for measuring a color unevenness defect of a solid-state imaging device equipped with a color filter, wherein the number of block divisions in the horizontal direction of the color filter is adjusted so that a horizontal repetition frequency is 500 ± 100 KHz. set, block division methods based on the output signal of the solid-state imaging device
Color unevenness defect caused by the color filter
An image measurement method characterized in that: 2. An image measuring method for measuring a color unevenness defect of a solid-state imaging device equipped with a color filter, wherein the number of block divisions in the horizontal direction of the color filter is adjusted so that a horizontal repetition frequency is 125 ± 25 KHz. set, block division methods based on the output signal of the solid-state imaging device
Color unevenness defect caused by the color filter
An image measurement method characterized in that: