Systems and methods for defect detection using a whole raw image

1. An apparatus for identifying a defect in an electronic circuit having periodic features, the apparatus comprising:

a. a camera for obtaining an image of the electronic circuit; and

b. an image processing system comprising a processing unit and a memory, the image processing system being configured to:

i. receive the image of the electronic circuit from the camera;

ii. perform a diagonal shift of the received image of the electronic circuit by at least a diagonal size of the periodic features of the electronic circuit to produce a shifted image of the electronic circuit;

iii. identify a candidate defect using the image of the electronic circuit and the shifted image of the electronic circuit;

iv. compute one or more local defect-free reference images of an area of the electronic circuit using at least one selected image area containing no defects in the proximity of the identified candidate defect; and

v. determine the defect in the electronic circuit using the computed defect-free reference image of the electronic circuit and the image of the electronic circuit.

2. The apparatus of claim 1 , further comprising an electro-optical transducer positioned in the proximity of the electronic circuit, wherein the voltage image of the electronic circuit created by the camera is obtained by imaging the electro-optical transducer.

3. The apparatus of claim 2 , wherein the image processing system is further configured to locate defects in the imaging path and cross-check the located imaging path defects against the determined defect in the voltage image such that the areas in the voltage image corresponding to modulator defects are excluded from the detection of defects in the electronic circuit.

4. The apparatus of claim 2 , wherein the imaging path defects are located by convolving, using a low-pass filter, a calibration image of the modulator to obtain the convolved calibration image, computing an absolute difference between the calibration image and the convolved calibration image to obtain a difference image and thresholding the difference image.

5. The apparatus of claim 1 , wherein the image processing system is configured to identify the candidate defect by subtracting the image of the electronic circuit and the diagonally shifted image of the electronic circuit and thresholding the resulting difference image.

6. The apparatus of claim 5 , wherein before thresholding, the resulting difference image is convolved using a low-pass filter and the thresholding is performed on the convolved difference image.

7. The apparatus of claim 6 , wherein a region of interest in the image of the electronic circuit is selected around the candidate defect.

8. The apparatus of claim 1 , wherein the image processing system is configured to determine the defect in the electronic circuit by thresholding an image region of interest around the candidate defect using the one or more computed local defect-free reference images of the area of the electronic circuit.

9. The apparatus of claim 1 , wherein the image processing system is configured to determine a defect in the electronic circuit by comparing a difference between the image region of interest around the candidate defect and the computed local defect-free reference image of the area of the electronic circuit with a threshold.

10. The apparatus of claim 1 , wherein the image processing system is configured to determine the defect in the electronic circuit by comparing the image region of interest around the candidate defect with a first computed defect-free reference image comprising minimum intensity values, determined over multiple instances of the defect-free reference image, and a second computed defect-free reference image comprising maximum intensity values, also determined over multiple instances of the defect free-reference image.

11. A method for identifying a defect in an electronic circuit having periodic features, method comprising:

a. obtaining an image of the electronic circuit using a camera;

b. performing a diagonal shift of the obtained image of the electronic circuit by at least a diagonal size of the periodic features of the electronic circuit to produce a shifted image of the electronic circuit;

c. identifying a candidate defect using the image of the electronic circuit and the shifted image of the electronic circuit;

d. computing one or more local defect-free reference images of an area of the electronic circuit using at least one selected image area in the closest possible proximity of the identified candidate defect; and

e. determining the defect in the electronic circuit using the computed defect-free reference image of the electronic circuit, the image of the electronic circuit, wherein b.-d. are performed by an image processing system comprising a processing unit and a memory.

12. The method of claim 11 , wherein the image of the electronic circuit created by the camera is obtained by imaging an electro-optical transducer.

13. The method of claim 11 , further comprising locating defects in the imaging path and cross-checking the located imaging path defects against the determined defect in the voltage image such that the areas in the voltage corresponding to modulator defects are excluded from the detection of defects in the electronic circuit.

14. The method of claim 13 , wherein the imaging path defects are located by convolving, using a low-pass filter, a calibration image of the modulator to obtain the convolved calibration image, computing an absolute difference between the calibration image and the convolved calibration image to obtain a difference image and thresholding the difference image.

15. The method of claim 11 , further comprising identifying a candidate defect by subtracting the image of the electronic circuit and the diagonally shifted image of the electronic circuit and thresholding the resulting difference image.

16. The method of claim 15 , wherein before thresholding, the resulting difference image is convolved using a low-pass filter and the thresholding is performed on the convolved difference image.

17. The method of claim 11 , further comprising determining the defect in the electronic circuit by thresholding the image region of interest around the defect candidate using the computed defect-free reference image of the area of the electronic circuit.

18. The method of claim 11 , further comprising determining the defect in the electronic circuit by comparing a difference between the image region of interest around the defect candidate and the computed defect-free reference image of the area of the electronic circuit with a threshold.

19. The method of claim 11 , further comprising determining the defect in the electronic circuit by comparing the image region of interest around the defect candidate with a first computed defect-free reference image comprising minimum intensity values, determined over multiple instances of the defect free-reference image and a second computed defect-free reference image comprising maximum intensity values, also determined over multiple instances of the defect free-reference image.

20. A non-transitory computer-readable medium embodying a set of instructions, which, when executed by one or more processing units of an image processing system, cause the one or more processing units to perform a method for identifying a defect in an electronic circuit having periodic features, method comprising:

a. obtaining an image of the electronic circuit using a camera;

b. performing a diagonal shift of the obtained image of the electronic circuit by at least a diagonal size of the periodic features of the electronic circuit to produce a shifted image of the electronic circuit;

c. identifying a candidate defect using the image of the electronic circuit and the shifted image of the electronic circuit;

d. computing one or more local defect-free reference images of an area of the electronic circuit using at least one selected image area in the closest possible proximity of the identified candidate defect; and

e. determining the defect in the electronic circuit using the one or more computed local defect-free reference images of the electronic circuit, the image of the electronic circuit, wherein

b.-d. are performed by an image processing system comprising the one or more processing units and a memory coupled to the one or more processing units.