Method and apparatus for inspecting lightness on the surface of an object

• US 5,296,942 A
• Filed: 01/09/1992
• Issued: 03/22/1994
• Est. Priority Date: 01/09/1991
• Status: Expired due to Fees

• Current Assignee: Nippondenso Co., Ltd. (DENSO Corporation)
• Original Assignee: Nippondenso Co., Ltd. (DENSO Corporation)
• Inventors: Asai, Toshihiro, Yokoyama, Yoshio, Hieda, Takashi
• Primary Examiner(s): Coles, Sr., Edward L.
• Assistant Examiner(s): Stoll, Thomas L.
• Application Number:
  US07/817,805
• Time in Patent Office: 803 Days
• Field of Search: 358/463, 358/464, 358/465, 358/466, 358/457, 358/461
• US Class Current: 358/461
• CPC Class Codes: G01J 1/42 using electric radiation detectors optical or mechanical part G01J1/04; by comparison with a reference light or electric value G01J1/10
• CPC Class Codes: G01N 2021/1765 Method using an image detector and processing of image signal
• CPC Class Codes: G06V 10/751 Comparing pixel values or logical combinations thereof, or feature values having positional relevance, e.g. template matching

Abstract

An appratus for inspecting lightness on the surface of an object having at least first and second surface portions different in lightness, wherein an image of the first and second surface portions of the object are taken under appropriate illumination, the taken image is memorized, first and second reference lightness of the first and second surface portions are defined respectively, whether or not each pixel of the taken image belongs to either one of pixel regions defining the first and second surface portions are determined in accordance with values defining preliminarily memorized pixel regions respectively, lightness difference between each pixel of the taken image corresponding to the first surface portion and the first reference lightness is calculated, lightness difference between each pixel of the taken image corresponding to the second surface portion and said second reference lightness are calculated, and quality in lightness on the surface of the object are determined on a basis of the respective lightness difference.

Claims

1. An apparatus for inspecting lightness of the surface of an object having at least first and second surface portions different in lightness, comprising:

first means for taking an image of the first and second surface portions of the object under appropriate illumination,

second means for memorizing a normal image defining the first and second surface portions as a reference image,

third means for memorizing allowable ranges of the lightness of the first and second surface portions as first and second allowable lightness ranges respectively,

fourth means for determining as to whether or not lightness of each pixel (hereinafter called as each taken pixel) of said taken image and lightness of each pixel (hereinafter called as each reference pixel) of said reference image corresponding to said each taken pixel belong to said first and second allowable lightness ranges respectively at each of said corresponding taken and reference pixels in sequence, and if so, defining each pair of said corresponding taken and reference pixels as a first or second pair of determined corresponding pixels in sequence,

fifth means for counting the number of said first pairs of determined corresponding pixels and the number of said second pairs of determined corresponding pixels respectively to be set as first and second count values in sequence,

sixth means for accumulating a difference in pixel lightness of said each first pair of determined corresponding pixels and a difference in pixel lightness of said each second pair of determined corresponding pixels respectively to be set as first and second accumulated values in sequence,

seventh means for averaging said first and second accumulated values in accordance with said first and second count values respectively to be set as first and second average values,

eighth means for correcting lightness of each taken pixel of said each first pair of determined corresponding pixels so that the lightness of each taken pixel of said each first pair of determined corresponding pixels approaches the lightness of said corresponding reference pixel in accordance with said first average value and for correcting lightness of each taken pixel of said each second pair of determined corresponding pixels so that the lightness of each taken pixel of said each second pair of determined pixels approaches the lightness of said corresponding reference pixel in accordance with said second average value, and

ninth means for forming a single corrected image from said taken image in accordance with correction performed by said eight means.

2. An apparatus as claimed in claim 1, wherein said fourth means includes comparator means for comparing the lightness of said each taken and reference pixel and for determining based on said comparison whether or not lightness of said each taken pixel and lightness of said each reference pixel corresponding to said each taken pixel belong to said first and second allowable lightness ranges respectively, and AND gate means arranged to perform logical multiplication between results of said comparison of respective lightness of said each taken and reference pixel so as to select said first or second pair of determined corresponding pixels.

3. An apparatus for inspecting lightness of the surface of an object having at least first and second surface portions different in lightness, comprising:

first means for taking an image of the first and second surface portions of the object under appropriate illumination,

first memory means for memorizing said taken image,

second memory means for memorizing normal image of the surface of the object as a reference image,

third means for accumulating lightness of each pixel of said taken image in accordance with addressing of each pixel of said reference image at each pixel belonging to first and second pixel regions corresponding to the first and second surface portions, said third means setting the accumulated lightness as first and second accumulated lightness data respectively,

fourth means for counting the number of pixels of said taken image in accordance with addressing of each pixel of said reference image at each pixel belonging to said first and second pixel regions and for setting said respective counted numbers as first and second counted pixel data respectively,

fifth means for dividing said first accumulated lightness data by said first counted pixel data to be set into a first dividend data and for dividing said second accumulated lightness data by said second counted pixel data to be set into a second divided data, and

sixth means for taking a lightness difference of said first divided data and lightness of each pixel of said taken image belonging to said first pixel region and for taking a lightness difference of said second divided data and lightness of each pixel of said taken image belonging to said second pixel region, said sixth means determining a fault portion of said taken image as lightness fault data in accordance with said respective lightness difference.

4. An apparatus as claimed in claim 3, wherein said second memory means is arranged to memorize images of normal contours of the first and second surface portions as a reference image having values indicative of the first and second surface portions respectively.

5. An apparatus for inspecting lightness of the surface of an object having at least first and second surface portions different in lightness, comprising:

first means for taking an image of first and second surface portions of said object under appropriate illumination;

memory means for memorizing the image of the first and second surface portions;

second means for preliminary memorizing values defining respective regions of the first and second surface portions and for determining to which of the memorized values respective pixels of the image belong;

third means for defining, on a basis of the determination of the memorized values, a first reference lightness of the first surface portion in accordance with lightness of all the pixels of the image corresponding with the first surface portion and for defining, on a basis of the determination of the memorized values, a second reference lightness of the second surface portion in accordance with lightness of all the pixels of the image corresponding with the second surface portion; and

fourth means for calculating a difference between the first reference lightness and each lightness of the pixels of the image corresponding with the first surface portion and a difference between the second reference lightness and each lightness of the pixels of the image corresponding with the second surface portion and for determining the quality in lightness of the surface of said object on a basis of the calculated differences.

6. A method of inspecting lightness of the surface of an object having at least first and second surface portions different in lightness, comprising the steps of:

a) taking an image of the first and second surface portions of said object under appropriate illumination;

b) memorizing the image of the first and second surface portions;

c) preliminarily memorizing values defining respective regions of the first and second surface portions and determining to which of the memorized values respective pixels of the image belong;

d) defining, on a basis of the determination of the memorized values, a first reference lightness of the first surface portion in accordance with lightness of all the pixels of the image corresponding with the first surface portion and defining, on a basis of the determination of the memorized values, a second reference lightness of the second surface portion in accordance with lightness of all the pixels of the image corresponding with the second surface portion;

e) calculating a difference between the first reference lightness and each lightness of the pixels of the image corresponding with the first surface portion and a difference between the second reference lightness and each lightness of the pixels of the image corresponding with the second surface portion; and

f) inspecting lightness of the surface of said object on a basis of the calculated differences.