Optical black calibration

• US 20080074513A1
• Filed: 09/21/2006
• Published: 03/27/2008
• Est. Priority Date: 09/21/2006
• Status: Active Grant

• Current Assignee: MediaTek Singapore Pte. Ltd. (MediaTek, Inc.)
• Original Assignee: NuCORE Technology, Inc. (MediaTek, Inc.)
• Inventors: Noguchi, Yasu
• Granted Patent: US 7,817,197 B2
• Time in Patent Office: Days
• US Class Current: 348/243
• CPC Class Codes: H04N 25/63 applied to dark current
• CPC Class Codes: H04N 25/71 Charge-coupled device [CCD] sensors; Charge-transfer registers specially adapted for CCD sensors

Abstract

Preview mode low-resolution readouts occur, and then a shutter button on a camera is pressed, which causes an image sensor cleanout operation to occur. Following the cleanout, a high-resolution readout occurs. As rows of sensor values are read, the first rows are rows corresponding to a pre-defined horizontally-extending shielded area. There are no valid area sensor elements to either side of the horizontally-extending area. Data values read from the horizontally-extending area are used to determine optical black (OB) values that are then used to adjust the valid area values read out of the image sensor in that same frame. The same OB values are used throughout the adjusting of the valid area values of the entire frame. No values from the preview readouts are used in the OB value determination, so there is a clean break between the preview mode OB level and the high-resolution capture OB level.

Claims

1. A method comprising:

(a) reading first data from an image sensor in a preview mode, wherein the image sensor includes a plurality of rows of sensor elements, wherein the image sensor has a horizontally extending edge, a vertically extending edge, a valid area of sensor elements and a horizontally-extending shielded area of sensor elements, wherein the horizontally-extending shielded area extends horizontally between the valid area and the horizontally extending edge;

(b) reading second data from the horizontally-extending shielded area in a capture mode;

(c) using the second data read in (b) to determine an optical black value (OB value);

(d) reading third data from the valid area in the capture mode, wherein the OB value is determined in (c) before a substantial amount of third data is read from the valid area in (d); and

(e) using the OB value determined in (c) to modify the third data read in (d) to obtain optical black adjusted data (OBAD), wherein the OB value is not changed until after third data has been read in (d) from substantially all the sensor elements of the valid area.

2. The method of claim 1, wherein the image sensor is an integrated circuit that has a surface area, and wherein the valid area occupies a majority of the surface area, and wherein the horizontally-extending shielded area is taken from the group consisting of:

a top shielded area that extends between a top edge of the integrated circuit and an upper portion of the valid area, and a bottom shielded area that extends between a bottom edge of the integrated circuit and a bottom portion of the valid area.

3. The method of claim 2, further comprising:

performing an image sensor cleanout operation after (a) and before (b).

4. The method of claim 1, wherein steps (a) through (e) are performed by an integrated circuit, the method further comprising:

loading information into the integrated circuit, wherein the integrated circuit uses the information to determine whether data read from the image sensor was read from the horizontally-extending shielded area.

5. The method of claim 2, wherein the modifying of (e) involves:

supplying the third data read from the valid area in (d) to a digital accumulator such that the digital accumulator outputs a digital value;

using a digital filter to filter a stream of digital values output from the digital accumulator, the digital filter outputting a filter output value;

storing the filter output value; and

subtracting the filter output value from third data read from the valid area in (d).

6. The method of claim 2, wherein the image sensor has a vertically-extending shielded area, and wherein the third data in (d) is from a first frame of image data, the method further comprising:

(f) reading data from the vertically-extending shielded area during a readout of the first frame of image data, and using the data read from the vertically-extending shielded area to determine a second optical black value (OB value);

(g) reading a second frame of image data from the valid area of the image sensor in the capture mode; and

(h) using the second OB value determined in (f) to modify the second frame of image data read in (g) to obtain second optical black adjusted data (OBAD).

7. The method of claim 3, wherein a low resolution frame of data is read out of the image sensor in (a), the low resolution frame being the last in a sequence of low resolution frames, and wherein the second and third data read in (b) and (d) is from a high resolution frame, and wherein the high resolution frame is the first high resolution frame of data to be read out of the image sensor after the low resolution frame that is read out in (a).

8. The method of claim 5, wherein the filter output value is stored in a register, wherein integrated circuit includes a port that is usable to write a value into the register.

9. The method of claim 2, wherein a first OB value is determined in (c) for a first color, wherein a second OB value is determined in (c) for a second color, wherein the first OB value is used in (e) to obtain optical black adjusted data (OBAD) for the first color, and wherein the second OB value is used in (e) to obtain optical block adjusted data (OBAD) for the second color.

10. An integrated circuit, comprising:

means for determining an optical black value (OB value) using first data read from a horizontally-extending shielded area of an image sensor, wherein the image sensor includes a plurality of horizontally-extending rows of sensor elements, wherein data can be read from the image sensor horizontally-extending row of sensor elements by horizontally-extending row of sensor elements, wherein the horizontally-extending shielded area extends between a horizontal edge of the image sensor and a valid area of the image sensor, wherein the first data is data from a first frame of image data, wherein no data from a frame of image data other than the first frame is used in the determining of the OB value, and wherein the OB value is determined before a substantial amount of first frame data from the valid area of the image sensor is read from the image sensor; and

a register that stores the OB value throughout substantially the entire time that first frame data is read out from the valid area of the image sensor.

11. The integrated circuit of claim 10, wherein the means includes:

a digital accumulator having a digital input port and a digital output port;

a digital filter having a digital input port that is coupled to the digital output port of the accumulator, the digital filter outputting the OB value to the register; and

a coordinator circuit that supplies a signal to the accumulator, the signal being indicative of a time when data from the horizontally-extending shielded area of the image sensor is present on the digital input port of the accumulator.

12. The integrated circuit of claim 10, wherein the means includes:

a plurality of registers that store information that is usable by the means to determine whether data in the integrated circuit is data read from the horizontally-extending shielded area of the image sensor.

13. The integrated circuit of claim 10, wherein the first frame is the first frame of data read out from the image sensor in a capture mode after an image sensor cleanout operation is performed.

14. The integrated circuit of claim 13, wherein the means is also for:

using data read from a vertically-extending shielded area of the image sensor during a readout of the first frame to generate a second OB value, wherein the second OB value is loaded into the register after the readout of the valid area for the first frame has been completed.

15. The integrated circuit of claim 12, further comprising:

a serial port, wherein a processor external to the integrated circuit can load the information into the plurality of registers via the serial port.

16. An analog front end (AFE) integrated circuit, comprising:

a first set of registers, the contents of which are usable by circuitry within the AFE to identify data read from a horizontally-extending shielded area of an image sensor;

a second set of registers, the contents of which are usable by the circuitry within the AFE to identify data read from a vertically-extending shielded area of the image sensor; and

a third set of registers, the contents of which are usable by the circuitry within the AFE to identify data read from a valid area of the image sensor, wherein the image sensor has a horizontally-extending edge and a vertically-extending edge, wherein the horizontally-extending shielded area extends between the valid area and the horizontally-extending edge, and wherein the vertically-extending shielded area extends between the valid area and the vertically extending edge.

17. The AFE of claim 16, wherein the circuitry uses data read from the horizontally-extending shielded area during a first full resolution readout to determine an optical black (OB) value, wherein the first full resolution readout is the first full resolution readout of the image sensor following an image sensor cleanout operation, and wherein the OB value is used to adjust image data read from the valid area during the first full resolution readout.

18. The AFE of claim 16, wherein the circuitry comprises:

a digital accumulator having a digital input port and a digital output port;

a digital filter having a digital input port that is coupled to the digital output port of the accumulator, the digital filter outputting the OB value;

a shadow register that receives the OB value from the digital filter and stores the OB value; and

a coordinator circuit that supplies a signal to the accumulator, the signal being indicative of a time when data from the horizontally-extending shielded area of the image sensor is present on the digital input port of the accumulator.

19. The AFE of claim 18, wherein the circuitry further comprises:

a serial port usable to load the first set of registers, the second set of registers, and the third set of registers from a source external to the AFE.

20. The AFE of claim 16, wherein the horizontally-extending shielded area of the image sensor extends from the vertically-extending edge of the image sensor, across the image sensor, and to a second vertically-extending edge of the image sensor.

21. A method, comprising:

(a) powering up an image sensor;

(b) reading first sensor data out of the image sensor, wherein the first sensor data is from a horizontally-extending shielded area of the image sensor, wherein the image sensor has a horizontally-extending edge;

(c) using the first sensor data to determine an optical black value (OB value);

(d) reading second sensor data out of the image sensor, wherein the second sensor data is from a valid area of the image sensor, wherein the horizontally-extending shielded area is at least partially between the valid area and the horizontally-extending edge; and

(e) using the OB value to modify the second sensor data to obtain optical black adjusted data (OBAD), wherein both the first sensor data and the second sensor data are from a single frame of image data, and wherein the single frame of image data is the first frame of image data read out of the image sensor after the powering up of (a).

22. The method of claim 21, wherein the first frame of image data is read out of the image sensor in a full-resolution readout mode.

23. The method of claim 22, wherein an integrated circuit (IC) reads the first and second sensor data out of the image sensor, wherein the IC determines the OB value in (c), wherein the IC uses the OB value in (e), and wherein the IC modifies the second sensor data in (e) while second sensor data is being read out of the image sensor in (d).