Scannerless range imaging system having high dynamic range

• US 6,707,054 B2
• Filed: 03/21/2002
• Issued: 03/16/2004
• Est. Priority Date: 03/21/2002
• Status: Expired due to Term

• Current Assignee: Monument Peak Ventures, LLC (Dominion Harbor Enterprises, LLC)
• Original Assignee: Eastman Kodak Company
• Inventors: Ray, Lawrence A
• Primary Examiner(s): Porta, David
• Assistant Examiner(s): Lee, Patrick J.
• Application Number:
  US10/103,640
• Publication Number:
  US 20030178549A1
• Time in Patent Office: 726 Days
• Field of Search: 250/208.1, 250/559.38, 250/214.R, 250/214.VT, 250/206, 250/226, 250/234, 250/201.5, 250/201.6, 356/5.15, 356/5.1, 356/5.01, 356/3, 356/4.1, 356/4.01, 396/89, 396/106, 396/109, 396/80, 396/111, 396/114, 396/119, 396/120, 382/106
• US Class Current: 250/559.38
• CPC Class Codes: G01S 17/36 with phase comparison between the received signal and the contemporaneously transmitted signal
• CPC Class Codes: G01S 17/894 3D imaging with simultaneous measurement of time-of-flight at a 2D array of receiver pixels, e.g. time-of-flight cameras or flash lidar
• CPC Class Codes: G01S 7/481 Constructional features, e.g. arrangements of optical elements
• CPC Class Codes: G01S 7/491 Details of non-pulse systems
• CPC Class Codes: G01S 7/4915 Time delay measurement, e.g. operational details for pixel components signal extraction and conditioning G01S7/493; Phase measurement
• CPC Class Codes: G01S 7/4918 Controlling received signal intensity, gain or exposure of sensor
• CPC Class Codes: H04N 2209/045 using mosaic colour filter
• CPC Class Codes: H04N 23/56 provided with illuminating means
• CPC Class Codes: H04N 23/70 Circuitry for compensating brightness variation in the scene

Abstract

A scannerless range imaging system includes an illumination system for illuminating a scene with modulated illumination of a predetermined modulation frequency, and an image intensifier receiving reflected modulated illumination and including a modulating stage for modulating the reflected modulated illumination from the scene with the predetermined modulation frequency. An image responsive element includes an array of individual pixels for capturing images output by the image intensifier, whereby the modulation of the reflected modulated illumination incorporates a phase delay corresponding to the distance of objects in the scene from the range imaging system. A transmittance filter, including a plurality of filter elements having a spatially varying pattern of transmittance, are arranged in a one-to-one mapping with respect to the pixels forming the image responsive element. The spatially varying pattern of transmittance provides a plurality of separate exposures which are subsequently combined to form an output image with an expanded dynamic range.

Claims

1. A scannerless range imaging system having extended dynamic range for capturing range information from illumination reflected from a scene, said scannerless range imaging system comprising:

an illumination system for illuminating the scene with modulated illumination of a predetermined modulation frequency, whereby some of the modulated illumination is reflected from objects in the scene;

an image intensifier receiving the reflected illumination and including a modulating stage for modulating the reflected modulated illumination from the scene with the predetermined modulation frequency;

an image responsive element arranged in an optical path of the image intensifier, said image responsive element including an array of individual pixels for capturing images output by the image intensifier, including at least one image corresponding to the reflected modulated illumination, whereby the modulation of the reflected modulated illumination incorporates a phase delay corresponding to the distance of objects in the scene from the range imaging system; and

a transmittance filter including a plurality of filter elements having a spatially varying pattern of transmittance, said filter elements arranged in a one-to-one mapping with respect to the pixels forming the image responsive element, whereby the spatially varying pattern of transmittance provides a plurality of separate exposures which are subsequently combined to form an output image with an expanded dynamic range.

2. The range imaging system claimed in claim 1 wherein said plurality of filter elements are arranged in a pattern of tiles, each tile containing a predetermined group of filter elements each providing a different level of transmittance.

3. The range imaging system as claimed in claim 1 wherein the transmittance filter is arranged on the image responsive element.

4. The range imaging system as claimed in claim 1 further comprising relay optics for imaging the output of the image intensifier onto the image responsive element.

5. The range imaging system as claimed in claim 1 wherein the transmittance filter includes color filter elements for generating a color texture image.

6. The range imaging system as claimed in claim 1 wherein the image intensifier includes a micro-channel plate.

7. The range imaging system as claimed in claim 1 wherein the image responsive element is an electronic image sensor.

8. The range imaging system as claimed in claim 1 further comprising means for storing the range images as a bundle of associated images.

9. The range imaging system as claimed in claim 1 wherein the image responsive element captures a plurality of range images corresponding to the reflected modulated illumination, wherein each range image incorporates the effect of the predetermined modulation frequency together with a phase offset unique for each image.

10. The range imaging system as claimed in claim 9 wherein each unique phase offset θ

is given by θ

₁=2π

i/3;

i=0,1,2.

11. The range imaging system as claimed in claim 1 wherein the illumination system includes a laser illuminator for producing the modulated illumination.

12. The range imaging system as claimed in claim 1 wherein the illumination system includes a plurality of light emitting diodes for producing the modulated illumination.

13. The range imaging system as claimed in claim 1 wherein the image intensifier includes a phosphor plate for emitting the intensified and modulated light and the transmittance filter is responsive within the spectrum of the phosphor plate.

14. A color scannerless range imaging system having extended dynamic range for capturing range information and color information from illumination reflected from a scene, said scannerless range imaging system comprising:

an illumination system for illuminating the scene with modulated illumination of a predetermined modulation frequency, whereby some of the modulated illumination is reflected from objects in the scene;

an image intensifier receiving the reflected illumination and including a modulating stage for modulating the reflected modulated illumination from the scene with the predetermined modulation frequency;

an image responsive element arranged in an optical path of the image intensifier, said image responsive element including an array of individual pixels for capturing images output by the image intensifier, including at least one image corresponding to the reflected modulated illumination, whereby the modulation of the reflected modulated illumination incorporates a phase delay corresponding to the distance of objects in the scene from the range imaging system; and

a transmittance filter including a plurality of color filter elements having a spatially varying pattern of transmittance and arranged relative to the image intensifier to provide a color texture image, said color filter elements arranged in a one-to-one mapping with respect to the pixels forming the image responsive element, whereby the spatially varying pattern of transmittance provides a plurality of separate color exposures which are subsequently combined to form an output image with an expanded dynamic range.

15. A method for obtaining high resolution range estimates in a scannerless range imaging system from a group of pixels having a spatially varying pattern of exposure provided by a transmittance filter overlying the pixels, wherein the system collects a bundle of images and each pixel has a corresponding bundle of illumination values, said method comprising the steps of:

(a) computing data comprising an initial range estimate and an initial phase estimate from a bundle of illumination values for a first pixel in the group;

(b) computing a data integrity measure for the bundle of illumination values from the first pixel, wherein the data integrity measure includes at least one of a correlation of fitted data, a determination of the number of pixels that are clipped, or a determination of the number of pixels having a low signal-to-noise ratio;

(c) accepting the initial range estimate if the data integrity measure is deemed adequate relative to an integrity threshold;

(d) if the bundle of illumination values is not acceptable, forming an error boundary relative to the initial range estimate;

(e) computing data integrity measures for the bundles of illumination values for neighboring pixels in the group and rank ordering the results;

(f) computing a phase estimate for the highest ranked pixel;

(g) accepting the phase estimate for the highest ranked pixel if the phase estimate is within the error boundary;

(h) otherwise, repeating steps (f) and (g) for the other neighboring pixels until an acceptable phase estimate is determined; and

(i) utilizing the phase estimate with other phase estimates similarly generated from other groups of pixels to provide a plurality of separate exposures which are subsequently combined to form an output image with an expanded dynamic range.