Image sensor and image processing method to acquire a high-sensitivity image

• US 8,508,637 B2
• Filed: 07/12/2010
• Issued: 08/13/2013
• Est. Priority Date: 07/14/2009
• Status: Active Grant

• Current Assignee: Samsung Electronics Co. Ltd.
• Original Assignee: Samsung Electronics Co. Ltd.
• Inventors: Song, Hyun-chul, Choe, Won-hee, Han, Sang-wook
• Primary Examiner(s): Hernndez Hernndez, Nelson D.
• Assistant Examiner(s): HOGUE, DENNIS A
• Application Number:
  US12/834,320
• Publication Number:
  US 20110013040A1
• Time in Patent Office: 1,128 Days
• Field of Search: 348/207.99, 348/222.1, 348/300, 348/308, 348/297, 348/362, 250/208.1, 702/81
• US Class Current: 348/297
• CPC Class Codes: H04N 23/71 Circuitry for evaluating the brightness variation
• CPC Class Codes: H04N 25/46 by combining or binning pixels
• CPC Class Codes: H04N 25/59 by controlling the amount of charge storable in the pixel, e.g. modification of the charge conversion ratio of the floating node capacitance
• CPC Class Codes: H04N 25/75 Circuitry for providing, modifying or processing image signals from the pixel array
• CPC Class Codes: H04N 25/771 comprising storage means other than floating diffusion

Abstract

Disclosed are an image sensor and a local binning method in which binning is applied selectively. For example, binning is applied to pixels having low illumination and binning is not applied to non-low illumination pixels. Information on pixels having low illumination for a first image frame may be stored and used to perform binning with respect to areas of a second image frame corresponding to low illumination pixel areas determined with respect to the first image frame.

Claims

1. An image sensor, comprising:

a pixel array comprising a plurality of unit pixels; and

a column readout circuit comprising a plurality of column readout units, each column readout unit provided for a line of the plurality of unit pixels, the column readout circuit being configured to;

acquire an image frame from the pixel array,

create low illumination area information indicating low illumination areas of the image frame, and

in response to another image frame being received, perform local binning on areas of the another image frame corresponding to the low illumination areas, wherein the low illumination area information of the image frame indicates which unit pixels of the plurality of unit pixels have low illumination, and the low illumination area information is stored in the plurality of unit pixels and read from the plurality of unit pixels through the column readout units.

2. The image sensor of claim 1, wherein the column readout circuit performs local binning on the areas corresponding to the low illumination areas in an analog domain using an image signal of the another image frame.

3. The image sensor of claim 2, wherein a column readout unit of the plurality of column readout units comprises:

a binning determination unit configured to;

determine whether an image signal output from a unit pixel is to be binned with an image signal of another unit pixel, based on low illumination information read from the unit pixel; and

perform binning using the image signal read from the another unit pixel on the same row according to the result of the determination;

a noise removing unit configured to remove noise from the image signal;

an analog-to-digital converter configured to convert the noise-removed image signal into a digital image signal;

a latch configured to store the digital image signal;

a low illumination determination unit configured to determine whether the image signal output from the unit pixel has low illumination using the digital image signal; and

a low illumination information updating unit configured to update previously stored low illumination information according to the result of the determination.

4. The image sensor of claim 3, wherein the updated low illumination information is stored in the unit pixel and used to determine through the binning determination unit whether binning is to be performed on an image signal of still another image frame during a processing period of the still another image frame.

5. The image sensor of claim 2, wherein a unit pixel of the plurality of unit pixels comprises:

a photodiode configured to receive light and create photocharges;

a transmission transistor connected to the photodiode, and configured to transfer the photocharges;

a floating diffusion node configured to accumulate the photocharges transferred from the transmission transistor;

a reset transistor configured to discharge the photocharges accumulated in the floating diffusion node;

a source follower transistor configured to amplify the photocharges accumulated in the floating diffusion node into a voltage signal; and

a selector transistor configured to selectively output an image signal of the unit pixel,

wherein a drain of the reset transistor is connected to a signal line configured to transfer low illumination information determined by a corresponding column readout unit and indicating whether a value output from the photodiode corresponds to low illumination in the image frame.

6. The image sensor of claim 5, wherein the low illumination information is stored in a capacitor of the floating diffusion node.

7. The image sensor of claim 5, wherein:

the low illumination information is stored in the floating diffusion node;

the low illumination information stored in the floating diffusion node and indicating whether an image signal of the image frame has low illumination is read from the floating diffusion node before the reset transistor is turned on to output a reset signal; and

after an image signal created by accumulation of photocharges of the photodiode for a current image frame is output, low illumination information indicating whether the image signal for the current image frame has low illumination is stored in the floating diffusion node.

8. The image sensor of claim 1, wherein the column readout circuit is further configured to control each unit pixel of the pixel array to perform local binning in a charge domain.

9. The image sensor of claim 8, wherein a column readout unit of the plurality of column readout units comprises:

a binning determination unit configured to;

determine whether an image signal output from a unit pixel is to be binned with an image signal of another unit pixel, based on low illumination information read from the unit pixel; and

generate a control signal to perform local binning in the charge domain according to the result of the determination;

a noise removing unit configured to remove noise from the image signal;

an analog-to-digital converter configured to convert the noise-removed image signal into a digital image signal;

a latch configured to store the digital image signal;

a low illumination determination unit configured to determine whether the image signal output from the unit pixel has low illumination using the digital image signal; and

a low illumination information updating unit configured to update the low illumination information according to the result of the determination.

10. The image sensor of claim 8, wherein binning is controlled for each unit pixel.

11. The image sensor of claim 10, wherein a unit pixel of the plurality of unit pixels comprises:

a photodiode configured to receive light and create photocharges;

a transmission transistor connected to the photodiode, and configured to transfer the photocharges;

a transmission control transistor configured to control the transmission transistor;

a floating diffusion node configured to accumulate the photocharges transferred from the transmission transistor;

a reset transistor configured to discharge the photocharges accumulated in the floating diffusion node;

a source follower transistor configured to amplify the photocharges accumulated in the floating diffusion node into a voltage signal; and

a selector transistor configured to selectively output an image signal of the unit pixel,

wherein a drain of the reset transistor is connected to a signal line configured to transmits low illumination information indicating low illumination or non-low illumination, and

wherein the floating diffusion node is connected to a node configured to receive photocharges transmitted from another photodiode.

12. The image sensor of claim 11, wherein, in response to both the transmission control transistor and the transmission transistor being turned on, the photocharges accumulated by the photodiode are transferred to the floating diffusion node.

13. The image sensor of claim 11, wherein the low illumination information is stored in a capacitor of the floating diffusion node.

14. The image sensor of claim 11, wherein the low illumination information is stored in the floating diffusion node,

the low illumination information stored in the floating diffusion node and indicating whether an image signal of the image frame has low illumination is read from the floating diffusion node before the reset transistor is turned on to output a reset signal, and

after an image signal created by accumulation of photocharges of the photodiode for a current image frame is output, low illumination information indicating whether the image signal for the current image frame has low illumination is stored in the floating diffusion node.

15. An image processing method performed by an image sensor, the method comprising:

creating low illumination area information indicating low illumination areas of an image frame received from a pixel array having a plurality of unit pixels;

storing the created low illumination area information in the plurality of unit pixels; and

in response to another image frame being received, performing local binning on areas of the another image frame corresponding to the low illumination areas indicated by the low illumination area information, wherein the low illumination area information of the image frame indicates which unit pixels of the plurality of unit pixels have low illumination.

16. The image processing method of claim 15, wherein the low illumination area information is stored in unit pixels included in the image sensor, or in a separate memory.

17. The image processing method of claim 15, wherein the low illumination area information is updated in response to a new image frame being received.

18. The image processing method of claim 15, wherein the local binning is performed in at least one of a charge domain and an analog domain.

19. The image processing method of claim 15, wherein the local binning is performed in a digital domain.

20. An image sensor, comprising:

an array configured to acquire an image;

a determination unit configured to identify pixels of an acquired image for selective binning, according to output values of the pixels, wherein the identified pixels of the acquired image have relatively low illumination compared to other pixels of the acquired image for selective binning; and

a binning unit configured to perform binning with respect to pixels of another acquired image corresponding to the pixels of the acquired image selected for binning, wherein information about the identified pixels of the acquired image with relative low illumination is stored in the pixels.

21. The image sensor of claim 20, wherein the determination unit is further configured to determine a pixel of the acquired image whose output value is equal to or less than a predetermined value, less than that of an adjacent pixel, or equal to or less than a predetermined value less than that of an adjacent pixel as a pixel with low illumination for selective binning.

22. The image sensor of claim 20, wherein:

the binning unit is further configured to perform binning with respect to pixels of the another acquired image corresponding to the pixels of the acquired image having low illumination.

23. The image sensor of claim 20, wherein:

the binning unit is further configured to perform binning with respect to pixels of a second image corresponding to the pixels of the acquired image having low illumination to produce a first processed image.

24. The image sensor of claim 23, wherein:

the determination unit is further configured to identify pixels of the second image having relatively low illumination compared to other pixels of the second image for selective binning; and

the binning unit is further configured to perform binning with respect to pixels of a third image corresponding to the pixels of the second image having low illumination to produce a second processed image.

25. The image sensor of claim 20, wherein:

the acquired image is provided by a predetermined number of pixels;

the determination unit is further configured to identify part of the predetermined number of pixels of the acquired image having relatively low illumination compared to other pixels of the acquired image for selective binning; and

the binning unit is further configured to perform binning with respect to pixels of the another acquired image corresponding to the part of the predetermined number of pixels of the acquired image having low illumination.

26. The image sensor of claim 20, wherein the binning is performed in at least one of a charge domain and an analog domain.

27. The image processing method of claim 20, wherein the local binning is performed in a digital domain.

28. An image processing method performed by an image sensor having an array, a determination unit and a binning unit, the method comprising:

acquiring an image by the array;

identifying, by the determination unit, pixels of the acquired image for selective binning, according to output values of the pixels, wherein the identified pixels of the acquired image have relatively low illumination compared to other pixels of the acquired image for selective binning;

binning, by the binning unit, with respect to pixels of another acquired image corresponding to the pixels of the acquired image selected for binning; and

storing information about the identified pixels of the acquired image with relative low illumination in the pixels.

29. The image processing method of claim 28, wherein the identifying comprises determining a pixel of the acquired image whose output value is equal to or less than a predetermined value, less than that of an adjacent pixel, or equal to or less than a predetermined value less than that of an adjacent pixel as a pixel with low illumination for selective binning.

30. The image processing method of claim 28, wherein:

the binning comprises binning with respect to pixels of the another acquired image corresponding to the pixels of the acquired image having low illumination to produce a first processed image.

31. The image processing method of claim 30, further comprising:

identifying, by the determination unit, pixels of the another acquired image having relatively low illumination compared to other pixels of the another acquired image for selective binning; and

binning, by the binning unit, with respect to pixels of still another acquired image corresponding to the pixels of the another acquired image having low illumination to produce a second processed image.

32. The image processing method of claim 28, wherein:

the acquired image is provided by a predetermined number of pixels;

the identifying comprises identifying part of the predetermined number of pixels of the acquired image having relatively low illumination compared to other pixels of the acquired image for selective binning; and

the binning comprises binning with respect to pixels of the another acquired image corresponding to the part of the predetermined number of pixels of the acquired image having low illumination.

33. The image processing method of claim 28, wherein the binning comprises binning in at least one of a charge domain and an analog domain.

34. The image processing method of claim 28, wherein the local binning is performed in a digital domain.

35. An electronics device, comprising:

a housing defining the electronics device; and

an image sensor comprising;

an array configured to acquire an image;

a determination unit configured to identify pixels of an acquired image for selective binning, according to output values of the pixels, wherein the identified pixels of the acquired image have relatively low illumination compared to other pixels of the acquired image for selective binning; and

a binning unit configured to perform binning with respect to pixels of another acquired image corresponding to the pixels of the acquired image selected for binning, wherein information about the identified pixels of the acquired image with relative low illumination is stored in the pixels.

36. The electronics device of claim 35, wherein the determination unit is further configured to determine a pixel of the acquired image whose output value is equal to or less than a predetermined value, less than that of an adjacent pixel, or equal to or less than a predetermined value less than that of an adjacent pixel as a pixel with low illumination for selective binning.

37. The electronics device of claim 35, wherein:

the binning unit is further configured to perform binning with respect to pixels of the another acquired image corresponding to the pixels of the acquired image having low illumination to produce a first processed image.

38. The electronics device of claim 37, wherein:

the determination unit is further configured to identify pixels of the another acquired image having relatively low illumination compared to other pixels of the another acquired image for selective binning; and

the binning unit is further configured to perform binning with respect to pixels of still another acquired image corresponding to the pixels of the another acquired image having low illumination to produce a second processed image.

39. The electronics device of claim 35, wherein:

the acquired image is provided by a predetermined number of pixels;

the determination unit is further configured to identify part of the predetermined number of pixels of the acquired image having relatively low illumination compared to other pixels of the acquired image for selective binning; and

the binning unit is further configured to perform binning with respect to pixels of the another acquired image corresponding to the part of the predetermined number of pixels of the acquired image having low illumination.

40. The electronics device of claim 35, wherein the binning is performed in at least one of a charge domain and, an analog domain.

41. The electronics device of claim 35, wherein the electronics device comprises one of a cellular/mobile phone, a personal digital assistant (PDA), a digital camera, a portable game console, an MP3 player, a portable/personal multimedia player (PMP), a handheld e-book, a portable tablet/laptop PC, a global positioning system (GPS) navigation, a camcorder, a robot, a security camera device, a web camera device, a television, a monitor, and a home-entertainment setup box.

42. The image processing method of claim 35, wherein the local binning is performed in a digital domain.