METHOD AND SYSTEM FOR SYNCHRONIZING A FLASH TO AN IMAGER

• US 20100026853A1
• Filed: 07/30/2008
• Published: 02/04/2010
• Est. Priority Date: 07/30/2008
• Status: Active Grant

• Current Assignee: Semiconductor Components Industries LLC (ON Semiconductor Corporation)
• Original Assignee: Micron Technology, Inc.
• Inventors: Mokhnatyuk, Alexander
• Granted Patent: US 8,994,877 B2
• Time in Patent Office: Days
• US Class Current: 348/240.200
• CPC Class Codes: H04N 23/69 Control of means for changing angle of the field of view, e.g. optical zoom objectives or electronic zooming
• CPC Class Codes: H04N 23/74 by influencing the scene brightness using illuminating means
• CPC Class Codes: H04N 25/531 by controlling rolling shutters in CMOS SSIS
• CPC Class Codes: H04N 5/2628 Alteration of picture size, shape, position or orientation, e.g. zooming, rotation, rolling, perspective, translation

Abstract

A digital camera system synchronizes a flash to an array of image sensing elements. The array of image sensing elements senses an image focused on the array by a lens. The system includes an array controller that implements an electronic rolling shutter to capture the image as a frame. The electronic rolling shutter includes read and reset pointers that the array controller scans through the array to capture integrated photo charges on the image sensing elements to generate the frame. The number of lines between the reset and read pointers defines the integration time of the imager. The system also includes a flash controller that synchronizes the flash to a portion of the frame. When the flash is activated, the camera system reduces the integration time and synchronizes the flash to the scanning of a selected portion of the array.

Claims

1. A digital imager comprising:

an array of image sensing elements, which captures an image by integrating photo-charges during an integration time;

a flash controller which activates a flash synchronous with the integration time of a portion of the array, the portion of the array being less than the entire array;

an array controller coupled to the flash controller, to control the array to capture, as pixel data, the image sensed by the array and, when the flash controller activates the flash, and to reduce the integration time of the array such that the portion of the array is in its integration time when the flash is activated; and

processing circuitry coupled to one of the array controller and the flash controller, the processing circuitry interpolating an image frame from the pixel data corresponding to the portion of the array when the flash controller activates the flash.

2. The digital imager of claim 1, wherein the portion of the array is a middle portion of the array and the processing circuitry implements a digital zoom to interpolate the image frame from the pixel data corresponding to the middle portion of the array.

3. The digital imager of claim 1, wherein the portion of the array is selected by a user of the digital imager.

4. The digital imager of claim 1, wherein:

the array comprises a plurality of rows, each row including a plurality of image sensing elements, the portion of the array corresponding to a set of rows of the plurality of rows,

the array controller;

maintains a read pointer and a reset pointer, the read pointer indicating a row in the array being read, the reset pointer indicating a row in the array being reset, and the read pointer trailing the reset pointer by a number of rows which, in part, defines the integration time, and

advances the read and reset pointers through the array to capture the image, and

the flash controller activates the flash based on one of a position of the read pointer and a position of the reset pointer.

5. The digital imager of claim 4, wherein the flash controller controls the flash to discharge when the read pointer is at a row previous to the set of rows.

6. The digital imager of claim 4, wherein the flash controller controls the flash to discharge when the reset pointer is at a row following the set of rows.

7. An imaging system comprising:

a flash;

an array of image sensing elements which senses an image of a scene;

a lens which focuses the image on the array of image sensing elements;

a controller which controls the array of image sensing elements to implement an electronic rolling shutter to capture at least a portion of the focused image, the electronic rolling shutter defining an integration interval for each sensing element in the array, and which controls the flash to illuminate the scene when a portion of the array of image sensing elements, corresponding to the portion of the focused image, is in its integration interval, the portion of the focused image being less than the entire focused image; and

processing circuitry coupled to at least one of the array controller and the flash controller, the processing circuitry providing image pixels representing the portion of the focused image responsive to the flash.

8. The imaging system of claim 7, wherein the processing circuitry further provides a digital zoom feature for isolating and expanding at least the portion of the focused image.

9. The imaging system of claim 8, wherein the digital zoom feature comprises:

an image cropper which crops the portion of the focused image;

a vertical interpolator which interpolates the pixel data representing the cropped portion of the focused image in a vertical dimension to provide vertically interpolated data; and

a horizontal interpolator which interpolates the vertically interpolated data in a horizontal dimension.

10. The imaging system of claim 9, wherein the interpolation performed by the vertical and horizontal interpolators depends upon a zoom level selected by a user of the imaging system.

11. The imaging system of claim 7, further comprising a memory, wherein the controller is configured to store at least the image pixels representing the portion of the focused image.

12. A method of capturing an image of a scene comprising:

sensing an image using an array of image sensing elements and scanning the array to provide pixel data representing the image;

activating a flash, synchronous to the scanning of the array, to illuminate the scene while a portion of the array of image sensing elements is sensing the image, wherein at least a further portion of the image sensing array is not sensing the image when the flash is activated;

providing frame data from the pixel data representing the sensed image, the frame data corresponding to the portion of the image sensing array, exclusive of the further portion of the image sensing array; and

outputting the provided frame data.

13. The method of claim 12, wherein the providing of the frame data from the pixel data further includes computing a digital zoom on the frame data to provide a zoomed image.

14. The method of claim 12, further comprising establishing an integration time for rows of the array, wherein:

the portion of the image sensing array is a middle portion of the array; and

the sensing of the image comprises;

exposing each row of the middle portion of the array to the scene for the integration time, and

reading out pixel data from the exposed rows of the middle portion of the array after each row of the middle portion is exposed to the portion of the image for the integration time.

15. The method of claim 14, wherein the sensing of the image further comprises:

maintaining a read pointer and a reset pointer, the read pointer indicating a row in the array to be read, the reset pointer indicating a row in the array to be reset, and the read pointer trailing the reset pointer by a number of rows which define the integration time,

advancing the read pointer through the middle portion of the array to sense the image, after the reset pointer has reset a last line in the middle portion of the array;

wherein the activating of the flash occurs after the last line in the middle portion of the array has been reset and before a first line in the middle portion of the array has been read.

16. The method of claim 14, wherein the establishing of the integration time comprises changing a number of rows between the read and reset pointers.

17. The method of claim 12, further comprising establishing an integration time for rows of the array, wherein:

the sensing of the image comprises;

exposing each of a plurality of rows of the array to the scene for an amount of time equal to the integration time, and

reading out pixel data from selected ones of the exposed plurality of rows each selected row being separated from a next selected row by at least one unselected row.

18. The method of claim 17, wherein the providing of the frame data comprises interpolating the frame data to provide interpolated lines corresponding in position in the image to the unselected rows in the array of image sensing elements.

19. A method of controlling an imaging system, comprising:

focusing an image of a scene on an array of image sensing elements;

controlling an electronic rolling shutter to capture the image as a frame; and

synchronizing a discharge of a flash to the capture of the image such that a selected portion of the array of image sensing elements is capturing the image when the flash is discharged and a further portion of the image frame, different from the selected portion, is not capturing the image when the flash is discharged.

20. The method of claim 19, further comprising:

binning signals provided by adjacent image sensing elements of the array when the flash is not activated; and

presenting the binned pixels for display as a preview of the image.

21. The method of claim 20, further including identifying, in the preview, a portion of the image corresponding to the selected portion of the array.

22. The method of claim 19, further comprising:

establishing an integration time for the array of image sensing elements;

while exposing each row of the array of image sensing elements corresponding to the selected portion of the frame to the image for an amount of time equal to the integration time, discharging a test flash to generate a test frame;

analyzing the test frame to determine whether the selected portion of the array of image sensing elements has been adequately exposed; and

adjusting the integration time to provide for adequate exposure of the array of image sensing elements,

wherein the controlling of the electronic rolling shutter to capture the image comprises exposing the each row of the array of image sensing elements corresponding to the selected portion of the frame to the scene for an amount of time equal to the adjusted integration time.

23. The method of claim 19, wherein the selected portion of the array of image sensing elements is a middle portion of the array and the method further comprises:

isolating pixel signals from the middle portion of the array when the flash is not activated; and

presenting the isolated pixels for display as a preview.

24. The method of claim 23, wherein the synchronizing of the discharge of the flash comprises synchronizing the discharge of the flash to a leading curtain of the middle portion of the array.

25. The method of claim 23, wherein the synchronizing of the discharge of the flash comprises synchronizing the discharge of the flash to a trailing curtain of the middle portion of the array.

26. A method of controlling a flash for an imager including an array of image sensing elements, comprising:

measuring an ambient light level;

setting an integration time based on the measured ambient light level and a known light level of the flash to establish a desired level of exposure for the array of image sensing elements;

capturing the image as a frame using the array of image sensing elements and a rolling shutter; and

discharging the flash synchronized to the rolling shutter while a middle portion of the array of image sensing elements is capturing the image.

27. The method of claim 26, wherein the measuring of the ambient light includes:

capturing a test image frame without discharging the flash; and

calculating a histogram of the test image frame to determine an exposure profile of the image;

wherein the step of setting the integration time includes setting the integration time based on the exposure profile of the image and the known light level of the flash.

28. The method of claim 26 wherein the setting the integration time includes:

discharging the flash as a test flash;

measuring an exposure of the middle portion of the array of image sensing elements exposed to the test flash; and

setting the integration time based on the measured exposure to establish a desired level of exposure for an image captured by the array of image sensing elements.