Adaptive Illumination for Color-Corrected Underwater Imaging

• US 20080084496A1
• Filed: 01/18/2007
• Published: 04/10/2008
• Est. Priority Date: 10/04/2006
• Status: Active Grant

• Current Assignee: Massachusetts Institute of Technology
• Original Assignee: Massachusetts Institute of Technology
• Inventors: Bahr, Alexander, Vasilescu, Iuliu, Detweiler, Carrick, Rus, Daniela
• Granted Patent: US 8,106,944 B2
• Time in Patent Office: Days
• US Class Current: 348/348
• CPC Class Codes: G03B 13/00 Viewfinders; Focusing aids for cameras; Means for focusing for cameras; Autofocus systems for cameras
• CPC Class Codes: H04N 23/10 for generating image signals from different wavelengths
• CPC Class Codes: H04N 23/74 by influencing the scene brightness using illuminating means

Abstract

Described are a method and an apparatus for color-corrected underwater imaging. A range to an underwater object to be imaged is determined and control values are selected according to the range. Control values are predetermined for a number of ranges according to an optimization of a color quality factor for each range based on the spectra of the optical sources used for illumination and the wavelength-dependent optical transmission of the water for the range. The optical power of each optical source is controlled according to a respective one of the selected control values. Advantageously, an acquired image requires no color correction as the adaptive illumination compensates for the wavelength-dependent losses in the light propagation path from the optical sources to the object and from the object to the imaging device.

Claims

1. An apparatus for color-corrected underwater imaging comprising:

a plurality of optical sources each having a unique optical spectrum;

a range sensor adapted to determine a range to an underwater object to be imaged;

a memory module; and

a processor in communication with the range sensor and the memory module, the processor selecting a plurality of predetermined control values from the memory module in response to a range determined by the range sensor, the processor controlling an optical power of each of the optical sources in response to the selected predetermined control values for color-corrected imaging of the underwater object at the determined range.

2. The apparatus of claim 1 wherein the optical sources comprise filtered flash elements.

3. The apparatus of claim 1 wherein the optical sources comprise light emitting diodes.

4. The apparatus of claim 1 further comprising a sensor adapted to receive an image of the underwater object.

5. The apparatus of claim 1 further comprising a depth sensor and an ambient light sensor, wherein the processor selects the predetermined control values from the memory module in response to the range determined by the range sensor, a depth determined by the depth sensor and an ambient light intensity determined by the ambient light sensor.

6. The apparatus of claim 1 wherein the sensor comprises one of a camera, a video camera and an eye.

7. The apparatus of claim 1 wherein the predetermined control values are determined in a calibration procedure to optimize a color quality factor.

8. The apparatus of claim 7 wherein the color quality factor is a color rendering index.

9. The apparatus of claim 7 wherein the color quality factor is determined with respect to a blackbody reference source.

10. A method for color-corrected underwater imaging, the method comprising:

determining a range to an underwater object to be imaged;

selecting a plurality of control values in response to the range, the control values being predetermined according to an optimization of a color quality factor for the range; and

for each of the selected control values, controlling an optical power of an illumination of the underwater object, each illumination having a unique optical spectrum, wherein an image of the underwater object is color-corrected.

11. The method of claim 10 further comprising receiving the color-corrected image on an image sensor.

12. The method of claim 10 wherein the image sensor comprises one of a camera, a video camera and an eye.

13. The method of claim 10 wherein the control value is predetermined according to an optimization of a color quality factor for the range and a depth of the underwater object.

14. The method of claim 10 wherein the color quality factor is a color rendering index.

15. The method of claim 10 wherein the color quality factor is determined with respect to a blackbody reference source.

16. A method for determining a plurality of control values for controlling illumination of an underwater object using a plurality of optical sources, the method comprising:

determining a water transmission spectrum for a plurality of ranges to the underwater object; and

for each range, determining a set of control values in response to an optimization of a color quality factor for the illumination, the color quality factor being determined in response to a sum of transmission spectra, each transmission spectrum being determined as a product of an optical spectrum of a respective one of the optical sources and the water transmission spectrum for the range.

17. The method of claim 16 wherein the range comprises a round-trip optical path between the optical sources and the underwater object.

18. The method of claim 16 wherein the color quality factor is a color rendering index.

19. A method for determining a plurality of control values for controlling illumination of an underwater object using a plurality of optical sources, the method comprising:

determining a water transmission spectrum for a plurality of ranges to the underwater object;

for each range, determining an ambient light transmission spectrum for a plurality of depths, each depth being a distance between a surface of the water and the underwater object; and

for each combination of one of the ranges and one of the depths, determining a set of control values in response to an optimization of a color quality factor for the illumination, the color quality factor being determined in response to a sum of transmission spectra for the range and an ambient light transmission spectrum for the depth and range, each transmission spectrum being determined as a product of an optical spectrum of a respective one of the optical sources and the water transmission spectrum for the range.

20. The method of claim 19 wherein the color quality factor is a color rendering index.

21. The method of claim 19 wherein the range comprises a round-trip optical path between the optical sources and the underwater object.

22. The method of claim 19 wherein the ambient light transmission spectrum is scaled according to a measurement of an ambient light intensity.

23. A method for color-corrected imaging of an underwater object, the method comprising:

selecting an RGB coefficient set from a plurality of RGB coefficient sets, each RGB coefficient set comprising an R scale factor, a G scale factor and a B scale factor for each of a red sensor, a green sensor and a blue sensor, the selection being made in response to an optical spectrum of an illumination source and a range to the underwater object; and

for each pixel in a plurality of pixels in an acquired image of the underwater object, transforming an RGB value comprising an R value, a G value and a B value of the pixel to a color-corrected RGB value based on a linear combination of the respective R scale factor, the G scale factor and the B scale factor in the selected RGB coefficient set,

wherein the RGB coefficient sets are predetermined for the optical spectrum of the illumination source for a plurality of ranges according to an optimization of a color quality factor.

24. The method of claim 23 wherein the color quality factor is a color rendering index.