Image processing methods for image sensors with phase detection pixels
View Patent ↗An image sensor may include a pixel array having image pixels for capturing image data and phase detection pixels for gathering phase information during automatic focusing operations. Phase detection pixels may form phase detection pixel pairs having first and second pixels with different angular responses. The first and second pixels may have color filters of the same color or may have color filters of different colors. The phase detection pixel pairs may be isolated from other phase detection pixel pairs in the array or may be arranged consecutively in a line. The phase detection pixels may, for example, be provided with color filters to match the color filter pattern of the pixel array. Processing circuitry may adjust red and green pixel signals from a phase detection pixel pair having a red and green color filter and may subsequently determine a phase difference using the adjusted pixel signals.
1. A method for processing pixel signals from a pair of phase detection pixels in a pixel array that includes image pixels and phase detection pixels, wherein the pair of phase detection pixels includes a first pixel and a second pixel having different angular responses, the method comprising:
with the first and second pixels, generating respective first and second pixel signals;
with processing circuitry, adjusting the first and second pixel signals to reduce a bias between the first and second pixel signals; and
with the processing circuitry, determining a phase difference associated with the first and second pixel signals using the adjusted first and second pixel signals.
2. The method defined in claim 1 wherein the first and second pixels are different colors.
3. The method defined in claim 1 wherein adjusting the first and second pixel signals comprises adjusting the first and second pixel signals using predetermined correction factors.
4. The method defined in claim 3 wherein the predetermined correction factors are spatially-dependent.
5. The method defined in claim 1 wherein adjusting the first and second pixel signals comprises:
during image capture operations, determining a bias value using at least one neighboring pair of phase detection pixels, wherein the at least one neighboring pair of phase detection pixels is within a vicinity of the pair of phase detection pixels; and
adjusting the first and second pixel signals using the bias value.
6. The method defined in claim 5 wherein determining the bias value comprises:
with the processing circuitry, identifying a flat region of an image, wherein the at least one neighboring pair of phase detection pixels is located in the flat region.
7. The method defined in claim 1 further comprising:
automatically adjusting the position of a lens formed over the pixel array based on the phase difference.
8. The method defined in claim 7 wherein adjusting the position of the lens comprises:
with the processing circuitry, determining a direction of lens movement needed based on the phase difference.
9. The method defined in claim 8 wherein adjusting the position of the lens comprises:
with the processing circuitry, determining a lens displacement value based on the phase difference.
10. A method for processing pixel signals from a pair of phase detection pixels in a pixel array that includes image pixels and phase detection pixels, wherein the pair of phase detection pixels includes a first pixel and a second pixel having different angular responses, the method comprising:
with the first and second pixels, generating respective first and second pixel signals;
with processing circuitry, determining a brightness gradient based on image pixel signals from neighboring image pixels, wherein the neighboring image pixels are located in a vicinity of the first and second pixels; and
replacing the first and second pixel signals with interpolated image pixel signals using the brightness gradient.
11. The method defined in claim 10 wherein the first and second pixels each include a first color filter, wherein determining the brightness gradient based on the image pixel signals from neighboring image pixels comprises determining the brightness gradient based on the image pixel signals from neighboring image pixels each having a second color filter, and wherein the first and second color filters are selected from the group consisting of: green filters and broadband filters.
12. The method defined in claim 10 further comprising:
with processing circuitry, adjusting the first and second pixel signals to reduce a bias between the first and second pixel signals; and
with the processing circuitry, determining a phase difference associated with the first and second pixel signals using the adjusted first and second pixel signals.
13. The method defined in claim 12 wherein adjusting the first and second pixel signals comprises adjusting the first and second pixel signals using predetermined correction factors.
14. The method defined in claim 13 wherein the predetermined correction factors are spatially-dependent.
15. The method defined in claim 12 wherein adjusting the first and second pixel signals comprises:
during image capture operations, determining a bias value using at least one neighboring pair of phase detection pixels, wherein the at least one neighboring pair of phase detection pixels is within a vicinity of the pair of phase detection pixels; and
adjusting the first and second pixel signals using the bias value.
16. The method defined in claim 15 wherein determining the bias value comprises:
with the processing circuitry, identifying a flat region of an image, wherein the at least one neighboring pair of phase detection pixels is located in the flat region.
17. The method defined in claim 15 wherein determining the bias value comprises determining the bias value based at least partly on the brightness gradient.
18. A method for processing pixel signals from a pair of phase detection pixels in a pixel array that includes image pixels and phase detection pixels, wherein the pair of phase detection pixels includes a first pixel and a second pixel having different angular responses, wherein the first pixel is located in a first column and a first row in the pixel array, and wherein the second pixel is located in a second column and a second row in the pixel array, the method comprising:
with the first and second pixels, generating respective first and second pixel signals;
with processing circuitry, adjusting the first and second pixel signals based on pixel signals from at least one neighboring pair of phase detection pixels, wherein the at least one neighboring pair of phase detection pixels is within a vicinity of the pair of phase detection pixels;
with the processing circuitry, determining a phase difference associated with the first and second pixel signals using the adjusted first and second pixel signals;
determining a brightness gradient associated with an edge using neighboring image pixels, wherein the neighboring image pixels are within the vicinity of the pair of phase detection pixels; and
determining a bias value based at least partly on the brightness gradient.
19. The method defined in claim 18 wherein determining the phase difference associated with the first and second pixel signals comprises applying the bias value to compensate for differences in the first and second pixel signals.