Image sensor systems and methods for multiple exposure imaging
View Patent ↗An imaging device may capture a composite image from multiple individual exposures. In each imaging pixel in the imaging device, charge accumulated from each of the individual exposures may be accumulated onto a storage node. The accumulated charge from all of the individual exposures in a single composite image may be read out from the storage node. The individual exposures may be separated by delay periods. The lengths of the individual exposures and delay periods may be determined automatically or set by a user such that each individual exposure is substantially free of motion blur, while the composite image illustrates a moving subject in multiple positions.
1. A method of operating with an image sensing pixel that includes a photodiode, a given transistor coupled between the photodiode and a bias voltage, a charge storage region, a global shutter transistor coupled between the photodiode and the charge storage region, a floating diffusion region, and a transfer transistor coupled between the charge storage region and the floating diffusion region, the method comprising:
with the photodiode, converting incident light into first accumulated charge during a first integration period;
following the first integration period and with the global shutter transistor, transferring the first accumulated charge from the photodiode to the charge storage region;
following the transfer of the first accumulated charge, resetting the photodiode with the given transistor;
after resetting the photodiode, converting incident light into second accumulated charge during a second integration period, wherein the first and second integration periods have substantially equal lengths; and
following the second integration period and with the global shutter transistor, transferring the second accumulated charge from the photodiode to the charge storage region such that the first and second accumulated charges are summed in the charge storage region as a combined accumulated charge, wherein resetting the photodiode comprises resetting the photodiode over a delay period, and wherein the delay period is at least a hundred times the length of the first integration period.
2. The method defined in claim 1 further comprising:
with the transfer transistor, transferring the combined accumulated charge from the charge storage region to the floating diffusion region.
3. The method defined in claim 1 further comprising:
with a user input device, receiving user input specifying the length of the delay period.
4. The method defined in claim 1 wherein the first and second integration periods comprise two of at least three integration periods in a composite image, the method further comprising:
with a user input device, receiving user input specifying the number of integration periods in the composite image.
5. The method defined in claim 1 wherein the first and second integration periods comprise two of at least three integration periods in a composite image, wherein the delay period comprises one of a plurality of delay periods, each delay period being between a respective pair of integration periods in the at least three integration periods, and wherein the integration periods together with the delay periods have a length of at least 250 milliseconds.
6. The method defined in claim 1 wherein the image sensing pixel further includes a source-follower transistor having a gate terminal coupled to the floating diffusion node and a source-drain terminal coupled to an output line, the method further comprising:
sensing, over the output line, a voltage output by the source-follower transistor and corresponding to the combined accumulated charge on the floating diffusion region.
7. A method of capturing a multiple exposure composite image, comprising:
determining an overall capture period;
dividing the overall capture period into a plurality of individual exposure times separated by delay periods, wherein each delay period is at least ten times the length of each individual exposure time;
with each imaging sensing pixel in an array of image sensing pixels, accumulating charge on a photodiode during each of the individual exposure times;
with each imaging sensing pixel in the array of image sensing pixels, combining charge accumulated over the plurality of exposure times in a semiconductor diode; and
with image readout circuitry, sensing the combined charge stored in each imaging sensing pixel in the array of image sensing pixels.
8. The method defined in claim 7 wherein determining the overall capture period comprises:
with a user input device, receiving user input specifying the overall capture period.
9. The method defined in claim 7 wherein determining the overall capture period comprises:
identifying a subject of interest;
determining the velocity of the subject of interest; and
determining the overall capture period based on the velocity of the subject of interest.
10. The method defined in claim 7 further comprising:
determining how many individual exposure times the overall capture period is divided into based on user input.
11. The method defined in claim 7 wherein the image sensing pixels comprise global shutter pixels.
12. The method defined in claim 7 wherein the image sensing pixels comprise rolling shutter pixels.
13. A method of capturing a multiple exposure image, comprising:
identifying a subject of interest;
determining the velocity of the subject of interest;
determining an overall capture period based on the velocity of the subject of interest;
based on the velocity of the subject of interest, dividing the overall capture period into a plurality of individual exposure times separated by delay periods, wherein each delay period is at least a hundred times the length of each individual exposure time;
with each imaging sensing pixel in an array of image sensing pixels, accumulating charge on a photodiode during each of the individual exposure times; and
with each imaging sensing pixel in the array of image sensing pixels, combining charge accumulated over the plurality of exposure times in a semiconductor diode.
14. The method defined in claim 13 wherein the image sensing pixels comprise global shutter pixels.
15. The method defined in claim 13 , wherein dividing the overall capture period into the plurality of individual exposure times separated by delay periods based on the velocity of the subject of interest comprises determining a length of the plurality of individual exposure times based on the velocity of the subject of interest and determining a length of the delay periods based on the velocity of the subject of interest.
16. The method defined in claim 15 , wherein determining the length of the plurality of individual exposure times based on the velocity of the subject of interest comprises determining the length of the plurality of individual exposure times such that the subject of interest is substantially free of motion blur in each individual exposure time.
17. The method defined in claim 16 , wherein determining the length of the delay periods based on the velocity of the subject of interest comprises determining the length of the delay periods such that the delay is long enough for the subject of interest to be in substantially different positions in at least some of the plurality of individual exposure times.
18. The method defined in claim 1 , wherein the delay period is at least a thousand times the length of the first integration period.
19. The method defined in claim 7 , wherein the semiconductor diode comprises a doped silicon region formed in a silicon substrate.