Optical filter opacity control in motion picture capture
The present invention comprises a system for and method of frequency prefiltering comprising a camera shutter capable of continuously variable illumination during a single exposure of the sensor. The shutter comprises a continuously variable exposure effector which in disposed in an image path, either in front of a lens or between a lens and a sensor. The system for frequency prefiltering further comprises a synchronization cable that synchronizes a drive system with a sensor or with film. The shutter further comprises a postfilter. The postfilter comprises a digital finite impulse response convolutional filter.
1. A system comprising:
an image sensor configured to generate a first plurality of consecutive image frames and a second plurality of consecutive image frames from light that contacts the image sensor;
an optical filter disposed in an optical path of the image sensor and having an opacity that is adjustable,
wherein the optical filter is configured to vary, responsive to a control signal, an amount of the light that contacts the image sensor; and
a processor configured to:
transmit the control signal to the optical filter,
generate the control signal to vary the opacity during first exposure windows for the first plurality of consecutive image frames to diminish an impact of temporal aliasing over the first plurality of consecutive image frames, and
generate the control signal to maintain the opacity constant at an opacity level other than fully transparent during second exposure windows for the second plurality of consecutive image frames.
2. The system of claim 1 , wherein the optical filter comprises a variable opacity liquid crystal.
3. The system of claim 2 , wherein the variable opacity liquid crystal is configured to, responsive to the control signal, maintain a substantially uniform opacity across its surface area.
4. The system of claim 1 , wherein the processor is configured to generate the control signal to continually vary the opacity during the first exposure windows.
5. The system of claim 1 , wherein the processor is configured to generate the control signal to vary the opacity during the first exposure windows so that a minimum opacity level of the optical filter during the first exposure windows occurs mid-way during each of the first exposure windows.
6. The system of claim 1 , wherein the opacity level is a 50% opacity for at least one of the second exposure windows.
7. The system of claim 1 , wherein the processor is configured to generate the control signal at least according to a user input received via a user interface.
8. The system of claim 1 , wherein an amplitude of the control signal varies over time, and the opacity varies during the first exposure windows and the second exposure windows corresponding to the amplitude of the control signal during the first exposure windows and the second exposure windows.
9. The system of claim 1 , wherein the control signal is a square wave.
10. The system of claim 1 , wherein the optical filter is disposed before the image sensor in the optical path and after a lens in the optical path so that the light passes through the lens and the optical filter before reaching the image sensor.
11. The system of claim 1 , further comprising a device housing configured to enclose the image sensor and the processor, the optical filter being disposed external to the device housing.
12. A method comprising:
generating, by a processor, a control signal to control an opacity of an optical filter disposed in an optical path of an image sensor;
varying the opacity during first exposure windows for first plurality of consecutive image frames to diminish an impact of temporal aliasing over the first plurality of consecutive image frames;
maintaining the opacity constant at an opacity level other than fully transparent during second exposure windows for second plurality of consecutive image frames; and
generating, by the image sensor, the first plurality of consecutive image frames and the second plurality of consecutive image frames responsive to light that contacts the image sensor.
13. The method of claim 12 , wherein the optical filter comprises a variable opacity liquid crystal.
14. The method of claim 12 , wherein said varying comprises continually varying the opacity during the first exposure windows.
15. The method of claim 12 , wherein a minimum opacity level of the optical filter during the first exposure windows occurs mid-way during each of the first exposure windows.
16. The method of claim 12 , further comprising passing the light through a lens disposed in the optical path before the light contacts the optical filter.
17. The method of claim 12 , further comprising positioning the optical filter external to a device housing that encloses the image sensor and the processor.
18. A system comprising:
an image sensor configured to generate a first plurality of consecutive image frames and a second plurality of consecutive image frames from light that contacts the image sensor;
an optical filter disposed in an optical path of the image sensor and having an opacity that is adjustable,
wherein the optical filter is configured to vary, responsive to a control signal, an amount of the light that contacts the image sensor; and
a processor configured to:
transmit the control signal to the optical filter,
generate the control signal to vary the opacity during first exposure windows for the first plurality of consecutive image frames to filter object motion above a Nyquist frequency over the first exposure windows, and
generate the control signal to maintain the opacity constant at an opacity level other than fully transparent during second exposure windows for the second plurality of consecutive image frames.
19. The system of claim 18 , wherein the optical filter comprises a variable opacity liquid crystal.
20. The system of claim 18 , wherein the processor is configured to generate the control signal to vary the opacity during the first exposure windows so that a minimum opacity level of the optical filter during the first exposure windows occurs mid-way during each of the first exposure windows.