Apparatus and method for calibrating image capture devices

• US 8,405,727 B2
• Filed: 09/26/2008
• Issued: 03/26/2013
• Est. Priority Date: 05/01/2008
• Status: Active Grant

• Current Assignee: Apple Inc.
• Original Assignee: Apple Inc.
• Inventors: Gere, David S., Chen, Ting, Bronstein, Chad Andrew
• Primary Examiner(s): Fan, Chieh M
• Assistant Examiner(s): Garces-Rivera, Angel L
• Application Number:
  US12/238,898
• Publication Number:
  US 20090273679A1
• Time in Patent Office: 1,642 Days
• Field of Search: None
• US Class Current: 348/187
• CPC Class Codes: H04N 17/002 for television cameras
• CPC Class Codes: H04N 23/843 Demosaicing, e.g. interpolating colour pixel values
• CPC Class Codes: H04N 25/134 based on three different wavelength filter elements
• CPC Class Codes: H04N 25/136 using complementary colours

Abstract

An apparatus and method are disclosed for calibrating image capture devices, such as the type used in electronic devices. In some embodiments, the electronic device may include at least one array of pixels and a memory coupled to the at least one array of pixels. The electronic device may further include a central processing unit (CPU) coupled to the memory and at least one color filter optically coupled to the at least one array of pixels. The memory may further include one or more storage locations that include a response of the at least one color filter to one or more predetermined wavelengths from a target test source, as well as, one or more storage locations that include a response of one or more baseline color filters.

Claims

1. An electronic image capture device, comprising:

an array of pixels configured for receiving wavelengths of light;

a filter coupled to the array of pixels and configured for filtering the wavelengths of light;

a processor coupled to the array and configured for;

selecting a correction value based on data received from the array and a baseline value, the baseline value being a ratiometric comparison of intensities of the wavelengths of light passing through a baseline filter; and

applying the correction value to an image captured by the device.

2. The electronic device of claim 1, wherein the baseline value is a ratiometric comparison of an intensity of a first one of the wavelengths of light to an intensity of a second one of the wavelengths of light.

3. The electronic device of claim 1, wherein the correction value comprises at least one correction constant.

4. The electronic device of claim 1, wherein one of the wavelengths includes a wavelength in the infrared spectrum.

5. The electronic device of claim 1, wherein:

the filter comprises an infrared blocking filter; and

one of the wavelengths includes a wavelength near the cut-off wavelength of the infrared blocking filter.

6. The electronic device of claim 1, wherein the baseline value is updated when a firmware executed by the processor is updated.

7. The electronic device of claim 1, wherein a response of the filter is calculated based on ratios of the wavelengths measured from a plurality of wavelength emanating regions.

8. The electronic device of claim 1, wherein the response of the filter is stored in one or more memory locations after the electronic device has been manufactured.

9. The electronic device of claim 1, wherein the data received from the array is measured in response to the wavelengths.

10. A method for calibrating an electronic image capture device, comprising:

storing, in a memory within the electronic device, a first color response of a baseline filter;

storing, in the memory within the electronic device, a second color response of a filter located within the electronic device to a light source having predetermined wavelengths;

comparing a first ratiometric value based on intensities of the first color response of the baseline filter with a second ratiometric value based on intensities of the second color response of the filter located within the electronic device,

wherein the first ratiometric value is determined based on a comparison of intensities of the predetermined wavelengths of light passing through the baseline filter; and

based on the comparison, adjusting the second color response of the filter located within the electronic device.

11. The method of claim 10, further comprising exposing the electronic device to a target test structure after the electronic device has been manufactured.

12. The method of claim 11, wherein the target test structure comprises calibration patterns that include a plurality of wavelength emanating regions.

13. The method of claim 12, further comprising measuring the intensity ratios of the filter located within the electronic device from at least two of the plurality of wavelength emanating regions.

14. The method of claim 13, wherein measuring the ratios of color responses is executed in a processor within the electronic device.

15. The method of claim 14, further comprising updating the first color response of the baseline filter when a firmware executed by the processor is updated.

16. The method of claim 10, wherein at least one of the predetermined wavelengths of light is in the infrared range.

17. The method of claim 10, further comprising determining the first color response of the baseline filter based on the light source having predetermined wavelengths.

18. A system for calibrating an image capture device comprising:

at least one color filter that is operative to react to a combination of a calibration pattern and a light source that is optically coupled to the at least one color filter;

a memory coupled to the at least one color filter, the memory comprising one or more storage locations; and

a processor accessing the memory;

wherein the calibration pattern comprises two or more regions that emanate a plurality of predetermined wavelengths;

wherein the two or more regions that emanate a plurality of predetermined wavelengths are oriented in substantially close physical proximity within the calibration pattern; and

wherein a comparison between outputs of at least two of the two or more regions that emanate predetermined wavelengths is stored in one or more storage locations of the memory.

19. The system of claim 18, wherein a response of one or more baseline color filters to the one or more regions that each emanates a predetermined wavelength is stored in the one or more storage locations of the memory.

20. The system of claim 19, wherein the comparisons between the outputs of at least two of the two or more regions that emanate predetermined wavelengths are ratiometric comparisons.