Multiple exposure methods and apparatus for electronic cameras
A method for capturing multiple sets of image data with an electronic camera having a shutter and an electronic shutter for selectively allowing light to reach an image sensor comprises opening the shutter and the electronic shutter, allowing light to reach the image sensor for a first exposure time, closing the electronic shutter, reading out pixel data captured during the first exposure time, allowing light to reach the image sensor for a second exposure time, and, reading out pixel data captured during the second exposure time. The method may be used to obtain multiple differently exposed images of a scene for combination into a high dynamic range image.
1 . A method of capturing an image with an electronic camera having a shutter for selectively allowing light to reach an image sensor and means for selectively reading out pixel data from the image sensor, the method comprising:
opening the shutter;
allowing light to reach the image sensor for a first exposure period;
preserving pixel data captured during the first exposure period; and,
allowing light to reach the image sensor for a second exposure period; and,
reading out pixel data captured during the first and second exposure periods.
2 . A method according to claim 1 comprising closing the shutter to end the second exposure period.
3 . A method according to claim 2 comprising closing the shutter prior to reading out the pixel data captured during the first and second exposure periods.
4 . A method according to claim 2 comprising reading out the pixel data captured during the first exposure period prior to closing the shutter.
5 . A method according to claim 3 wherein the first exposure period is different in length from the second exposure period.
6 . A method according to claim 5 wherein the first exposure period is longer than the second exposure period.
7 . A method according to claim 1 wherein the first exposure period is different in length from the second exposure period.
8 . A method according to claim 7 wherein the first exposure period is longer than the second exposure period.
9 . A method according to claim 7 comprising, in the electronic camera, combining the pixel data captured during the first and second exposure periods to yield high dynamic range data and saving the high dynamic range data in a data store accessible to the camera.
10 . A method according to claim 1 wherein preserving pixel data captured during the first exposure period comprises shifting the pixel data from pixel registers into vertical registers of the image sensor.
11 . A method according to claim 1 wherein reading out pixel data from the first exposure period is performed while allowing light to reach the image sensor for the second exposure period.
12 . A method according to claim 11 comprising, after the second exposure period, preserving pixel data captured during the second exposure period and allowing light to reach the image sensor for a third exposure period.
13 . A method according to claim 12 wherein the first, second and third exposure periods are all of different lengths.
14 . A method according to claim 11 comprising compensating for smearing of the pixel data from the first exposure period by a method comprising comparing the pixel data for the first exposure period to corresponding pixel data for at least one of the second and third exposure periods.
15 . A program product comprising a medium carrying computer-readable instructions which, when executed by a processor in a controller for a camera, cause the controller to control the camera to perform a method according to claim 1 .
16 . A method for capturing an image with an electronic camera having a shutter and an interline transfer charge coupled device comprising a plurality of pixels, each pixel configured to acquire charge dependent on an amount incoming light received at the pixel, and a plurality of vertical registers configured to receive pixel data from the pixels, the method comprising:
opening the shutter and clearing any charge stored on the pixels;
capturing charge at the pixels for a first exposure period;
shifting first exposure pixel data comprising charges captured during the first exposure period from the pixels to the vertical registers;
capturing charge at the pixels for a second exposure period;
shifting the first exposure pixel data from the vertical registers and reading out the first exposure pixel data;
after reading out the first exposure pixel data, shifting second exposure pixel data comprising charges captured during the second exposure period from the pixels to the vertical registers;
shifting the second exposure pixel data from the vertical registers and reading out the second exposure pixel data; and, after an end of the second exposure period, closing the shutter.
17 . A method according to claim 16 wherein the first and second exposure periods are different in length.
18 . A method according to claim 17 wherein the first exposure period is longer than the second exposure period.
19 . A method according to claim 16 comprising setting an aperture of the camera differently for the first and second exposure periods.
20 . A method according to claim 16 comprising determining the first and second exposure times based on an aperture setting of the camera.
21 . A method according to claim 16 comprising shifting the first exposure pixel data from the vertical registers and reading out the first exposure pixel data after closing the shutter.
22 . A method according to claim 16 comprising shifting the first exposure pixel data from the vertical registers and reading out the first exposure pixel data during the second exposure period.
23 . A method according to claim 22 comprising, before closing the shutter, and after shifting the second exposure pixel data to the vertical registers, capturing charge at the pixels for a third exposure period.
24 . A method according to claim 23 wherein shifting the second exposure pixel data from the vertical registers and reading out the second exposure pixel data are performed after closing the shutter and the method comprises:
after reading out the second exposure pixel data, shifting third exposure pixel data comprising charges captured during the third exposure period from the pixels to the vertical registers; and,
shifting the third exposure pixel data from the vertical registers and reading out the third exposure pixel data.
25 . A method according to claim 24 comprising compensating for smearing of the pixel data from the first exposure period by a method comprising comparing the pixel data for the first exposure period to corresponding pixel data for at least one of the second and third exposure periods.
26 . A program product comprising a medium carrying computer-readable instructions which, when executed by a processor in a controller for a camera, cause the controller to control the camera to perform a method according to claim 16 .
27 . An electronic camera comprising an image sensor array, a shutter for selectively allowing light to reach the image sensor array, readout circuitry for selectively reading out pixel data from the image sensor and a controller configured to control the shutter and the readout circuitry the controller comprising a processor and a memory having computer-readable code embodied therein which, when executed by the processor, causes the controller to open the shutter and, while the shutter is open:
allow light to reach the image sensor for a first exposure period;
preserve pixel data captured during the first exposure period; and,
allow light to reach the image sensor for a second exposure period.
28 . A camera according to claim 27 wherein the code causes the controller to read out pixel data captured during the first and second exposure periods after closing the shutter.
29 . A camera according to claim 28 wherein the first exposure period is different in length from the second exposure period.
30 . A camera according to claim 29 wherein the first exposure period is longer than the second exposure period.
31 . A camera according to claim 27 wherein the image sensor comprises a plurality of pixel registers and a plurality of vertical registers and the code causes the controller to preserve the pixel data captured during the first exposure period by shifting the pixel data from the pixel registers of the image sensor into the vertical registers of the image sensor.
32 . A camera according to claim 1 wherein the code causes the processor to read out the pixel data from the first exposure period while allowing light to reach the image sensor for the second exposure period.
33 . A camera according to claim 28 wherein the controller is configured to store the pixel data captured during the first and second exposure periods on a digital storage medium.
34 . A camera according to claim 28 wherein the controller is configured to generate HDR image data by combining the pixel data captured during the first and second exposure periods and to store the HDR image data on a digital storage medium.
35 . A camera according to claim 27 wherein the image sensor comprises an interline transfer CCD array.