JP2001153752A - Method for evaluating quality of diffusion plate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize a method for evaluating quality of a diffusion plate whereby the quality of the diffusion plate can be inspected at a good reproducibility, without the personal judgment. SOLUTION: A light from a surface light source 1 irradiates the diffusion plate 3 through a pattern mask 2, the diffusion plate 3 is photographed by a camera 4, and the degree of dispersion of the pixel outputs of the taken image is calculated and processed to evaluate the quality of the diffusion plate, based on the degree of dispersion thereof.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for evaluating the quality of a diffusion plate of a liquid crystal display device.

[0002]

2. Description of the Related Art In a display screen of a liquid crystal display device, if the distribution of luminance is not smooth, the image is reflected on a glaring screen. Therefore, the incident light is scattered and transmitted, and the light transmittance,
In order to improve light diffusibility, improve front luminance, and reduce luminance unevenness, a diffusion plate that diffuses light is incorporated in the screen. Conventionally, when inspecting this diffusion plate, an expert
The degree of glare of the diffusion plate (a state in which small bright spots can be seen flickering) was visually checked.

[0003]

However, in the visual inspection, there is a problem that reliable data cannot be obtained, for example, the result of the inspection varies depending on the skill of the inspector. Accordingly, an object of the present invention is to realize a method for evaluating the quality of a diffusion plate that can inspect the quality of the diffusion plate with good reproducibility regardless of human judgment.

[0004]

According to the method for evaluating the quality of a diffuser according to the present invention, light from a surface light source is applied to the diffuser through a pattern mask, the diffuser is imaged by a camera, and each pixel output of the image is obtained. Is a method of calculating the degree of variation of the diffusion plate and evaluating the quality of the diffusion plate based on the degree of variation. Here, as a method of determining the “degree of variation”, any method can be adopted as long as the method has reproducibility. For example, if each pixel output is written as Xn (n = 1, 2, 3,...), Xn
Σ ² σ ² = E ｛(Xn− <X>) ²ら れ る (where E ｛represents an operation for averaging, and <X> is an average value E ｛of Xn) Xn｝) or based on the standard deviation σ. Alternatively, the determination may be made by dividing the variance value or the standard deviation by <X>.

According to the method of the present invention, the degree of glare of the diffuser can be objectively evaluated by statistical processing of each pixel output of an image picked up by a camera, so that the evaluation is objective and accurate. Can be secured.

[0006]

Embodiments of the present invention will be described below in detail with reference to the accompanying drawings. FIG. 1 is a schematic view of an apparatus for evaluating the quality of a diffusion plate. Surface light source 1
A pattern mask 2 is set on the substrate, and a diffusion plate 3 to be measured is set thereon. Although the surface light source 1 uses a plurality of leaky optical fibers arranged in a plane, the light source is not limited to this as long as it emits light in a planar shape, and a light source having any configuration may be used. .

The pattern mask 2 is formed by forming a pattern with lines on a transparent film. Although the pattern mask used here is the pattern mask of the vertical and horizontal black lattice pattern 21 shown in FIG. 2, the present invention is not limited to this, and a pattern mask composed of any pattern may be used. However, when the pattern pitch of the pattern mask 2 is compared with the pixel pitch on the imaging surface of the CCD camera 4, the pattern pitch is preferably coarser than the pixel pitch. In other words, it is preferable that the spatial frequency of the pattern of the pattern mask 2 is lower than the spatial frequency of the pixel array on the imaging surface.

The diffuser plate 3 is imaged by a CCD camera 4 in focus on the surface of the diffuser plate 3, and the data of each pixel output of the imaged image is input to a personal computer 5. The number of pixels captured by the CCD camera 4 is at least three.
The number is preferably 0 or more, and the more the number, the more preferable. The personal computer 5 obtains an average value, a variance, and a standard deviation of each pixel output by statistical processing, and compares the variance or the standard deviation with a threshold value.
Assess the quality of.

[0009]

EXAMPLE A diffusion plate 3 was mounted on a pattern mask 2 having a vertical pitch b of 300 μm and a horizontal pitch a of 100 μm, and an image was taken by a CCD camera 4. In this case, CCD
Since the degree of variance changes depending on the F value of the camera 4, the F value with the largest variance was found (F = 8), and an image was captured with this F value fixed. The number of pixels of the CCD camera 4 is 512
× 512, image processing was performed in a range of 490 × 490 pixels excluding the end portion. The actual image processing area is
50.7 mm ² .

[0010] The diffusion plate 3 is a transparent resin having a fine surface irregularity structure containing fine particles having an average particle size in the range of 0.005 to 50 µm, preferably 0.5 to 5 µm, on one surface of the light-transmitting support film. It has a layer (diffusible resin layer). As the support film, a polarizing film, a retardation film, a transparent film, or the like is used. The material and thickness of the support film are not particularly limited. Eleven samples of the diffusion plate 3 were prepared, and output gradation data (0 to 256) of each pixel was measured and totaled for one diffusion plate to calculate a variance value. In addition, the degree of glare of each sample was measured visually.

Table 1 shows the variance data of the eleven samples.

[0012]

[Table 1]

The samples in Table 1 are numbered from 1 to 11 in ascending order of visual glare. FIG. 3 shows a graph of the results in Table 1. As can be seen from Table 1 and FIG. 3, only the sample numbers 2 and 3 show that the visual glare degree and the variance data are reversed, and otherwise, the correlation between the visual evaluation and the data evaluation. Is out.

Therefore, it has been found that the degree of glare of the diffusion plate can be evaluated by the method of the present invention in the same manner as in the conventional visual observation.

[0015]

As described above, according to the method for evaluating the quality of a diffuser according to the present invention, the diffuser is imaged with a camera, and statistical processing of the output of each pixel is performed to reduce the glare of the diffuser without any human labor. The degree can be evaluated objectively. Therefore, the yield of the quality inspection of the diffusion plate can be increased without impairing the reliability of the inspection result.

[Brief description of the drawings]

FIG. 1 is a schematic layout view of an apparatus for evaluating the quality of a diffusion plate.

FIG. 2 is a view showing a pattern mask of a vertical and horizontal black lattice pattern, wherein a represents a horizontal pitch and b represents a vertical pitch.

FIG. 3 is a graph in which dispersion data of a diffusion plate is plotted.

[Explanation of symbols]

 1 surface light source 2 pattern mask 3 diffusion plate 4 CCD camera 5 personal computer

Claims (1)

[Claims] A light from a surface light source is applied to a diffusion plate through a pattern mask, an image of the diffusion plate is taken by a camera, and a degree of variation of each pixel output of the captured image is calculated and processed based on the degree of the variation. And evaluating the quality of the diffusion plate.