Liquid crystal panel inspection method

• US 5,394,481 A
• Filed: 01/15/1992
• Issued: 02/28/1995
• Est. Priority Date: 01/16/1991
• Status: Expired due to Fees

• Current Assignee: YOZAN, Inc.
• Original Assignee: Ezel, Inc.
• Inventors: Hiiro, Kaoru, Shimizu, Harumi, Takahashi, Tooru, Kumagai, Ryohei, Oosaka, Manabu
• Primary Examiner(s): Boudreau, Leo H.
• Assistant Examiner(s): Cammarata, Michael
• Application Number:
  US07/820,925
• Time in Patent Office: 1,140 Days
• Field of Search: 382/48, 382/8, 382/21, 382/22, 382/41
• US Class Current: 382/141
• CPC Class Codes: G01N 2021/9513 Liquid crystal panels
• CPC Class Codes: G01N 21/88 Investigating the presence of flaws or contamination

Abstract

A method of inspecting a liquid crystal panel and determining the type of defect. Each part of the liquid crystal panel is extracted and inspected by comparison with an extracted reference part. The parts to be inspected may be found based on the location of previously found parts or by examining a plot of the density in the image. Vector data from a part that is known to be defectless is used to extract the reference part. Alternatively, the contour of a reference part may be determined by analyzing the vector data which was obtained for the parts to be inspected. The type of defect is determined by classifying the defective part according to characteristics of the part'"'"'s image (e.g., brightness of the pixels) as compared with parts having known defects.

Claims

1. A method of inspecting a liquid crystal panel for defects, comprising the steps of:

i) inputting an image of a single liquid crystal panel wherein said liquid crystal panel contains parts;

ii) generating density projection data for said image of said liquid crystal panel;

iii) selecting a single defectless one of said liquid crystal panel parts as a single reference part and determining a vectorization starting point on said single reference part using said density projection data;

iv) generating a vectorized contour of said single reference part using said vectorization starting point; and

v) examining all other parts in said liquid crystal panel, which are to be inspected, by making a comparison with said single reference part based on said vectorized contour to determine which of said all other parts are defective.

3. The method of claim 1, wherein step v) comprises the step of finding coordinates for each said other part by searching an area which is within a tolerance of a predetermined distance from said single reference part.

4. The method of claim 1, wherein step iii) includes the steps of:

iii_a) extracting, from said image of said liquid crystal panel, the vectorized contours of each said part;

iii_b) creating a histogram for each said part based upon the extracted contours;

iii_c) classifying said parts into groups based on their histogram; and

iii_d) selecting, as said single reference part, a part from said group having the most members.

5. The method of claim 4, wherein step ii_d) includes the steps of:

iii_d1) calculating a mean density from said histograms;

iii_d2) selecting, as said single reference part, a part which has said mean density from said group having the most members.

2. A method of inspecting a liquid crystal panel for defects, comprising the steps of:

i) inputting an image of a liquid crystal panel, wherein said liquid crystal panel contains parts;

ii) selecting a defectless one of said liquid crystal panel parts as a reference part and determining a vectorization starting point on said reference part;

iii) generating a contour of said reference part using said vectorization starting point; and

iv) examining all other parts in said liquid crystal panel, which are to be inspected, by making a comparison with said reference part based on said contour, where in said examination includes the following steps;

iv_a) generating density projection data for said image of said liquid crystal panel;

iv_b) differentiating said density projection data;

iv_c) defining the following three points as candidates for being edges of a part;

a) a point on which said differentiated data changes from 0 to minus;

b) a point on which said differentiated data changes from plus to 0; and

c) a point on which said differentiated data changes from minus to plus;

iv_d) calculating the mean density between said points which are adjacent to each other;

iv_e) defining a threshold for each said point to be a predetermined value multiplied by said mean density; and

iv_f) defining, for each said point, said point to be an edge of a part when said density projection value for said point is less than or equal to said threshold for that point.

7. The method of claim 2, wherein density projection data is generated along a diagonal contour line.

6. A method of inspecting a liquid crystal panel for defects, comprising the steps of:

i) inputting an image of a liquid crystal panel, wherein said liquid crystal panel contains parts;

ii) selecting a defectless one of said liquid crystal panel parts as a reference part and determining a vectorization starting point on said reference part, wherein said determination of said vectorization starting point includes the following steps;

ii_a) generating density projection data for said image of said liquid crystal panel;

ii_b) differentiating said density projection data;

ii_c) selecting a minimum value from said differentiated density projection data;

ii_d) using said minimal value to define a vectorization starting point corresponding to a reference part.

iii) generating a contour of said reference part using said vectorization starting point; and

iv) examining all other parts in said liquid crystal panel, which are to be inspected, by making a comparison with said reference part based on said contour.