Compensating for vignetting
A system including an image capture system with a sensing efficiency that varies over a field of view of the image capture system may employ shaped illumination to compensate for the variation in the sensing efficiency. An illuminator may be configured to illuminate the field of view of the image capture system with illumination shaped to have higher intensity where the sensing efficiency is lower, e.g., at the periphery of the field over view. The imaging system may thus provide image data with more uniform signal-to-noise ratios. Image data from an illuminated scene may be manipulated using data from a non-illuminated scene to produce improved image data.
1. A system, comprising:
a camera having a sensing efficiency that varies over a field of view of the camera;
a lighting system configured to illuminate the field of view of the camera, the lighting system configured to generate illumination having a distribution shaped to have higher intensity where the sensing efficiency is lower, the illumination having an intensity at a center of the field of view that is lower than an intensity of the illumination at an edge of the field of view; and
a processor configured to manipulate a first image data corresponding to a scene illuminated by the lighting system using a second image data corresponding to the scene with ambient lighting.
2. The system of claim 1 , wherein image data representing a scene and captured by the camera has a substantially uniform signal-to-noise ratio as a result of the illumination.
3. The system of claim 1 , wherein the first image data is combined with the second image data.
4. The system of claim 1 , wherein the second image data is removed from the first image data.
5. The system of claim 1 , wherein the lighting system is configured to produce rotationally symmetric illumination.
6. The system of claim 1 , wherein the lighting system comprises an array of semiconductor lasers.
7. The system of claim 6 , wherein the lighting system further comprises a diffuser positioned to control divergence of beams from the semiconductor lasers.
8. A system, comprising:
a camera having a sensing efficiency that varies over a field of view of the camera;
a lighting system configured to illuminate the field of view of the camera, the lighting system configured to generate illumination having a distribution shaped to have higher intensity where the sensing efficiency is lower, the lighting system comprising:
a light source; and
a lens configured to direct a first intensity of light from the light source to a first area of the field of view and configured to direct a second intensity of the light from the light source to a second area of the field of view, the second area corresponding to where the camera's sensing efficiency is lower, the second intensity being greater than the first intensity; and
a processor configured to manipulate first image data, corresponding to a scene illuminated by the lighting system, using second image data, corresponding to the scene with ambient lighting.
9. The system of claim 8 , wherein the light source is configured to produce light from a source area, and the light from the source area is spatially non-uniform.
10. The system of claim 9 , wherein the light source comprises a plurality of light elements that are distributed over the source area and operated to produce the spatially non-uniform illumination.
11. The system of claim 8 , wherein the lens is configured to alter illumination from the light source so that the illumination from the lighting system has a rectangular cross-section.
12. The system of claim 8 , wherein the source area is located in a focal plane of the lens.
13. A method for collecting image data, the method comprising:
determining a sensing efficiency of an image capture system at a plurality of points;
illuminating a scene with illumination having a shaped distribution with higher intensity where the sensing efficiency of the image capture system is lower;
using the image capture system to capture first image data representing the scene as illuminated with the illumination having the shaped distribution; and
using the image capture system to capture second image data representing the scene in ambient light without the illumination having the shaped distribution.
14. The method of claim 13 , wherein the illumination is brighter at a periphery of a field of view of the imaging system than the illumination is at a center of the field of view of the imaging system.
15. The method of claim 13 , further comprising combining the first image data and the second image data to produce third image data that has a substantially uniform signal-to-noise ratio.
16. The method of claim 13 , further comprising subtracting at least a portion of the second image data, representing the scene in ambient light, from the first image data, representing the scene as illuminated with the illumination having the shaped distribution, to produce third image data that has a substantially uniform signal-to-noise ratio.
17. The method of claim 13 , wherein the image capture system is configured to capture the first image data representing the scene as illuminated with the illumination having the shaped distribution based on a characteristic of the illumination.
18. The method of claim 17 , wherein the characteristic of the illumination is selected from the group consisting of a polarization, a wavelength, and a frequency.