Image quality inspection system and image synthesis method

An image quality inspection system to test a display panel with high resolution and low cost by forming a synthesized contrast image of the display panel is disclosed. The image quality inspection system includes a camera section with a built-in image element to capture the image contrast data of the display panel, a rotating plate holding optical filters, an optical lens section having a focal adjustment mechanism for forming an image on the camera section, two parallel plates to move the image by thickness and rotating tilt angles of the plates, a plurality of motors to drive the parallel plates and the parallel plates, an A/D conversion section that converts the image contrast data output from the camera section to digital signals, an image memory that stores the contrast data converted to the digital signal, an image synthesis memory that performs an image fitting process in accordance with image motion controls by the parallel plates and produces a single image of the display panel, and a CPU control section that controls an image synthesis process in the image synthesis memory.

FIELD OF THE INVENTION 
This invention relates to an image quality inspection system and an image 
synthesis method for obtaining high resolution images of display panel 
with low cost. 
BACKGROUND OF THE INVENTION 
When measuring the contrast of pixels of an object to be inspected using a 
CCD (Charge Coupled Device) camera in the image inspection of a flat panel 
display, such as a LCD (Liquid Crystal Display) panel, being able to take 
in the contrast of pixels of a LCD panel to be inspected with the small 
number of CCD pixels is the prerequisite for inexpensive, accurate and 
suitable inspection system used in the production line. 
Traditionally, in order to create an image by measuring the contrast of a 
LCD panel having a pixel size of 300 .mu.m.sup.2, for example, by a CCD 
camera, many CCD pixels are required to correspond to a single LCD pixel 
for specifying a position of the LCD pixel. For example, 36 CCD pixels 
have been corresponded to a single LCD pixel. 
In the method utilizing many CCD pixels corresponding to a single LCD 
pixel, it is required to increase the density of CCD pixels, which makes 
the CCD expensive. 
SUMMARY OF THE INVENTION 
Therefore, an objective of this invention is to provide an image quality 
inspection system which is able to measure the contrast of a LCD panel 
accurately and in high resolution with a small number of CCD pixels when 
measuring the LCD panel using a CCD camera. 
In order to achieve this objective, in this invention, a camera section 
with a built-in image element such as CCD is arranged to capture the image 
contrast data of a display panel to be inspected such as a LCD panel. For 
a color image, four optical filters of red, green, blue and transparency 
are installed on a rotating plate in order to measure the brightness of 
red, green and blue separately or the brightness of white. In addition, an 
optical lens section having a focal adjustment mechanism for forming an 
image on the camera section is arranged. A plane parallel plate for the X 
direction and a plane parallel plate for the Y direction are arranged to 
allow the image to be moved by the glass thickness and rotating tilt 
angle. The above rotating plate, the plane parallel plate for the X 
direction and the plane parallel plate for the Y direction are driven by 
corresponding motors, each motor of which is controlled by a motor control 
section. The image contrast data output from the camera section is 
converted to digital signals by an A/D conversion section and stored 
temporarily in an image memory. The image contrast data obtained by image 
motion control in the X and Y directions using the plane parallel plates 
is processed for image fitting corresponding to the movements and stored 
in an image synthesis memory as a single image of the image element. The 
image synthesis control and motor control are performed, then, the image 
synthesis data is processed and the detection of image defects are carried 
out in a CPU control section. 
The image synthesis of the present invention is performed as follows. 
Firstly, the image of a panel to be inspected without the movement in the 
X and Y directions by the plane parallel plates is taken in by the image 
element and stored in the image memory, and further stored in the image 
synthesis memory. Next, the image of the display panel is moved by 
controlling the rotating tilt angle of the plane parallel plates and the 
resulted image contrast data of the panel to be inspected is stored in the 
image memory, and further processed to fit in the position corresponding 
to the movement of the image in the synthesis memory. For example, when 
the image is moved in the X direction, the image data is stored at the 
memory location corresponding to the movement in the X direction in 
contrast with the image data with no movement. A single image of the image 
element is obtained by performing the image fitting process on the image 
synthesis memory by the image movement controlled by the rotating tilt 
angle of the plane parallel plates, storing the moved image in the image 
memory, and further repeating the fitting process of the image synthesis 
memory to the position corresponding to the movement. As a result, high 
resolution measurements with the smaller number of pixels of the image 
element are possible in contrast with the number of pixels of the panel to 
be inspected. 
The image inspection system as composed above can increase the measuring 
resolution without increasing the number of pixels of the image element in 
contrast with the number of pixels of the display panel to be inspected, 
hence, it makes the highly accurate measurements possible with low cost.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
FIG. 1 is a diagram showing the basic structure of the image quality 
inspection system in accordance with the present invention. This image 
inspection system comprises: an image element, for example a camera 
section 19 with a built-in CCD for capturing an image contrast data of a 
display panel 10 to be inspected; a rotating plate 14 to capture an image 
through 4 optical filters of R (Red), G (Green), B (Blue), and 
transparency which are attached to the rotating plate; an optical lens 
section 13 having a focal adjustment mechanism for forming an image on the 
camera section 19; a plane parallel plate for the X direction 11 and plane 
parallel plate for the Y direction 12 which allow the image to be moved by 
the glass thickness and rotating tilt angle within an approximate stroke 
of 400 .mu.m with an accuracy of several .mu.m; a motor 15 for rotating 
the rotating plate 14, a motor 16 for rotating the plane parallel plate 11 
for the X direction and a motor 17 for rotating the plane parallel plate 
12 for the Y direction; a motor control section 18 that controls each of 
the motors 15-17; an A/D conversion section 20 that converts the image 
contrast data output from the camera section 19 to digital signals; an 
image memory 21 to temporarily store the contrast data from the A/D 
conversion section 20; an image synthesis memory 22 that performs the 
image fitting process in accordance with the image motion control in the X 
and Y directions by the plane parallel plates to form a single CCD image; 
a CPU control section 23 that performs the image synthesis control and 
motor control, processes the image synthesis data and carries out the 
detection of image defects. 
Note that an aperture function can be added to the optical lens section 13 
to optimize the image formed on the camera section 19. 
FIG. 2 shows a flowchart of control process when the image shift is not 
performed by the plane parallel plates. In this case, 4 CCD pixels are 
assigned for a single LCD pixel. Hence, a LCD panel with 640.times.480 
pixels can be taken into a CCD camera with 1280.times.960 pixels. 
FIG. 4 shows the principle of a tilt and thickness of the plane parallel 
glass with both sides of the faces polished in flat and parallel to each 
other when a glass is used as the plane parallel plates 11 and 12, and the 
principle of the image shift of the panel to be inspected. When the plane 
parallel glass 30 is in parallel with the display panel 10 to be tested as 
shown in FIG. 4(a), the image on the panel 10 advances straight into the 
plane parallel glass 30. Whereas when the plane parallel glass 30 is 
tilted as shown in FIG. 4(b), the image on the panel is taken in with the 
shifted distance d due to refraction of the glass. 
FIG. 5 illustrates a flowchart of the control for capturing an image when 
the single LCD pixel is 300 .mu.m square, four CCD pixels are used for a 
single LCD pixel and the image shifts by the plane parallel plates 11 and 
12 are set to 75 .mu.m in the X and Y directions. In this case, the image 
taken in with 4.times.4=16 pixels/one LCD pixel is obtained in the image 
synthesis memory 22 and data equivalent to 16 CCD pixel resolution per one 
LCD pixel can be obtained. Overall, LCD with 640.times.480 pixels can be 
taken in as data equivalent to CCD with 2560.times.1920 pixels in the 
image synthesis memory 22 as shown in FIG. 6. 
FIG. 7 illustrates a flowchart of the control for capturing an image when 
the single LCD pixel is 300 .mu.m square, 4 CCD pixels are used for a 
single LCD pixel and the image shifts by the plane parallel plates 11 and 
12 are set to 50 .mu.m and 100 .mu.m in the X and Y directions, 
respectively. In this case, the image taken in with 6.times.6=36 pixels 
per one LCD pixel is obtained in the image synthesis memory 22 and data 
equivalent to 36 CCD pixel resolution per one LCD pixel can be obtained. 
Overall, LCD with 640.times.480 pixels can be taken in as data equivalent 
to CCD with 3840.times.2880 pixels in the image synthesis memory 22 as 
shown in FIG. 8. 
As the LCD image can be arbitrarily shifted in the X and Y directions by 
the plane parallel plates 11 and 12, data can be obtained by shifting 50 
.mu.m and 100 .mu.m only in the X direction as shown in FIG. 9(a) or data 
can be obtained by shifting 50 .mu.m and 100 .mu.m only in the Y direction 
as shown in FIG. 9(b). 
From the foregoing, the direction of the movement and the moving distance 
can be selected depending on the kind of defects of the object to be 
inspected because the movement of the LCD image by the plane parallel 
plate can be set by a program. 
Note that the above description was made in detail with a LCD panel as a 
panel to be inspected and CCD as an image element, but this invention is 
not limited by these cases. It extends to a flat panel in general such as 
an EL (Electro-Luminescence) panel and plasma display panel, and further 
MOS (Metal Oxide Semiconductor) type sensors as an image element. 
As this invention is composed as explained above, the resolution can be 
increased without increasing the number of pixels of the image element 
with respect to the number of pixels of the panel to be inspected. In 
addition, it can obtain low cost and high resolution images as the pixel 
density of the image element can be reduced.