Image Sensor Blemish Detection

1 . A system comprising:

an image sensor configured to capture images; and

a processing apparatus configured to:

obtain a test image from the image sensor;

apply a low-pass filter to the test image to obtain a blurred image;

determine an enhanced image based on a difference between the blurred image and the test image; and

compare image portions of the enhanced image to a threshold to determine whether there is a blemish of the image sensor.

2 . The system of claim 1 , in which the processing apparatus is configured to:

determine a blemish map by applying the threshold to the enhanced image.

3 . The system of claim 1 , in which applying the low-pass filter to the test image comprises convolving a square average kernel with the test image.

4 . The system of claim 1 , in which the test image is based on an image captured while a test surface is positioned in a field of view of the image sensor.

5 - 15 . (canceled)

16 . The system of claim 4 , in which the test surface is a light emitting diode panel.

17 . The system of claim 4 , in which the test surface is illuminated with uniform brightness across the field of view.

18 . The system of claim 1 , in which applying the low-pass filter to the test image comprises:

down-sampling the test image to obtain a down-sampled test image; and

applying the low-pass filter to the down-sampled test image.

19 . The system of claim 1 , in which the test image is a luminance level image.

20 . The system of claim 19 , in which obtaining the test image from the image sensor comprises:

obtaining a raw test image from the image sensor; and

apply one or more pre-processing operations to the raw test image to obtain the test image, wherein the one or more pre-processing operations include at least one of black level adjustment, white balance, demosaicing, or color transformation.

21 . The system of claim 1 , in which the processing apparatus is configured to:

store, transmit, or display an indication of whether there is a blemish of the image sensor.

22 . A method comprising:

obtaining a test image from an image sensor;

applying a low-pass filter to the test image to obtain a blurred image;

determining an enhanced image based on a difference between the blurred image and the test image;

comparing image portions of the enhanced image to a threshold to determine whether there is a blemish of the image sensor; and

storing, transmitting, or displaying an indication of whether there is a blemish of the image sensor.

23 . The method of claim 22 , comprising:

determining a blemish map by applying the threshold to the enhanced image.

24 . The method of claim 22 , in which applying the low-pass filter to the test image comprises convolving a square average kernel with the test image.

25 . The method of claim 22 , in which the test image is based on an image captured while a test surface is positioned in a field of view of the image sensor.

26 . The method of claim 25 , in which the test surface is a light emitting diode panel.

27 . The method of claim 25 , in which the test surface is illuminated with uniform brightness across the field of view.

28 . The method of claim 22 , in which applying the low-pass filter to the test image comprises:

down-sampling the test image to obtain a down-sampled test image; and

applying the low-pass filter to the down-sampled test image.

29 . A system comprising:

a test surface configured to be illuminated;

a holder configured to hold a camera in a position such that the test surface appears within a field of view of an image sensor of the camera; and

a processing apparatus configured to:

receive a test image from the camera, wherein the test image is based on an image captured by the image sensor in which the test surface appears within the field of view;

apply a low-pass filter to the test image to obtain a blurred image;

determine an enhanced image based on a difference between the blurred image and the test image; and

compare image portions of the enhanced image to a threshold to determine whether there is a blemish of the image sensor.

30 . The system of claim 29 , in which the test surface is a light emitting diode panel.

31 . The system of claim 29 , in which the test surface is illuminated with uniform brightness across the field of view.