LCD error detection system

• US 4,870,357 A
• Filed: 06/03/1988
• Issued: 09/26/1989
• Est. Priority Date: 06/03/1988
• Status: Expired due to Term

• Current Assignee: Apple Inc.
• Original Assignee: Apple Computer Incorporated (Apple Inc.)
• Inventors: Young, Steve, Foster, Nigel
• Primary Examiner(s): Eisenzopf, Reinhard J.
• Assistant Examiner(s): Urban, Edward F.
• Application Number:
  US07/202,875
• Time in Patent Office: 480 Days
• Field of Search: 324/158 R, 324/158 D, 324/73 R, 358/106, 358/107, 358/139, 356/237, 382/34, 250/492.2
• US Class Current: 324/760.01
• CPC Class Codes: G01R 31/308 using non-ionising electromagnetic radiation, e.g. optical radiation investigating or analysing materials by the use of optical means G01N21/00; image analysis G06T7/00

Abstract

The present invention is an error detection system for liquid crystal display (LCD) devices. The system comprises a photo-scanning device coupled to a computer and a LCD display driver. Faulty LCD cells are detected by using the photo-scanner to produce two images. The first image is produced by displaying a predetermined pattern on the LCD device. This pattern is inverted to produce the second image. By analyzing these two images, faulty LCD cells are located. The results of the analysis give the location of the faulty LCD cells.

Claims

1. A process for detecting faulty liquid crystal display (LCD) cells in an (LCD) device comprising the steps:

(1) displaying a first image (image A) on said LCD device;

(2) scanning and electronically storing said first image;

(3) displaying a second image (image B) on said LCD device where said second image is the inverse of said first image;

(4) scanning and electronically storing said second image;

(5) generating a third image (image A+B) from the matrix addition of said first and second images;

(6) selecting a threshold value to minimize processing time;

(7) analyzing a thresholded image generated from said third image;

(8) generating a bit map from said threshold image;

(9) locating the position of faulty LCD cells in said LCD device after conducting a connectivity analysis on said bit map;

(10) outputting the results of said locating step, such that the locations of said faulty LCD cells are provided.

2. The process as described in claim 1 further comprising a balancing step before said generating step wherein said first and said second images are balanced by first, calculating the lowest intensity value associated with a pixel of said images, second, calculating the highest intensity value associated with a pixel of said images and third, normalizing the contrast of said images.

3. The process as described in claim 2, wherein said step of balancing further comprises checking the purity of said LCD device by comparing the uniformity of the background intensity at various locations in said images with an average background intensity.

4. The process as described in claim 3, wherein said analyzing step further comprises using histogram analysis such that a majority of intensity values are cleared, leaving a minority of said intensity values indicating said faulty LCD cells.

5. The process as described in claim 4, wherein said locating step further comprises using a connectivity analysis, such that regions containing faulty LCD cells are determined by examining a collection of locations that have an intensity value associated with the presence of faulty LCD cells and the borders of said regions are ascertained, allowing the possibility of correcting said faulty LCD cells.

6. The process as described in claim 1, wherein further comprising producing a patterned image prior to displaying said image A, then checking cross talk by comparing the average intensity of areas of said LCD device that are directly horizontally or vertically adjacent to patterned areas of said LCD device with an average background intensity of said LCD device.

7. The process as described in claim 6, wherein said outputting step further comprises presenting an interface on a computer monitor for allowing a user to view said images by user selectable thresholding values and said user also having the ability to view histograms showing the relative frequency of intensity values in said images.

8. The process as described in claim 7, wherein said outputting step further comprises storing locations of said faulty LCD cells in a permanent storage file.

9. A liquid crystal display (LCD) error detection system comprising:

scanner means for producing electronic images of a LCD device;

LCD display driver means, coupled to said LCD device, for generating display signals to operate said LCD device;

computing means, coupled to said scanner means and said LCD display driver means, for electronically storing said images of said LCD device, performing analysis on said images to locate the position of faulty LCD cells, and outputting the results of said analysis;

said computing means coordinating operation of said scanner means and said LCD display driver means such that appropriate patterns appear on said LCD device to produce a first and second image wherein said LCD device has an inverted display for said second image.