Chromatic aberration correction in imaging system including variable focal length lens

Patent metadata

Field	Value
Publication number	US-9774765-B2
Application number	US-201514854624-A
Country	US
Kind code	B2
Filing date	Sep 15, 2015
Priority date	Sep 15, 2015
Publication date	Sep 26, 2017
Grant date	Sep 26, 2017

Abstract

An image acquisition system is operated to provide an image that is relatively free of the effect of longitudinal chromatic aberration. The system includes a variable focal length lens (e.g., a tunable acoustic gradient index of refraction lens) that is operated to periodically modulate a focus position. First, second, third, etc., wavelength image exposure contributions are provided by operating an illumination system to provide instances of strobed illumination of first, second, third, etc., wavelengths (e.g., green, blue, red, etc.) timed to correspond with respective phase timings of the periodically modulated focus position which focus the respective wavelength image exposure contributions at the same focus plane. The respective phase timings of the periodically modulated focus position compensate for longitudinal chromatic aberration of at least the variable focal length lens. An image is produced that is relatively free of the effect of longitudinal chromatic aberration by combining the image exposure contributions.

First claim

The invention claimed is:

1. A method for operating an image acquisition system to provide an image that is relatively free of an effect of longitudinal chromatic aberration in one or more lenses of the image acquisition system, the image acquisition system comprising an imaging system including a variable focal length lens, an illumination system, and a controller, the method comprising:
operating the variable focal length lens to periodically modulate a focus position of the imaging system over a plurality of focus positions along a Z-height direction;
providing a first wavelength image exposure contribution by operating the illumination system to provide an instance of strobed illumination of a first wavelength timed to correspond with a first phase timing of the periodically modulated focus position which focuses the first wavelength image exposure contribution at a first focus plane;
providing a second wavelength image exposure contribution by operating the illumination system to provide an instance of strobed illumination of a second wavelength timed to correspond with a second phase timing of the periodically modulated focus position which compensates for longitudinal chromatic aberration of at least the variable focal length lens and focuses the second wavelength image exposure contribution at the first focus plane, wherein the second wavelength is different than the first wavelength and the second phase timing occurs after the first phase timing; and
providing a wavelength combining image that is relatively free of the effect of longitudinal chromatic aberration by combining the first and second wavelength image exposure contributions, wherein the combining of the first and second wavelength image exposure contributions to provide the wavelength combining image comprises providing both the first and second wavelength image exposure contributions during a single image integration period of a detector of the imaging system.

2. The method of claim 1 , wherein:
the illumination system includes first and second sources of illumination;
the operating of the illumination system to provide the instance of strobed illumination of the first wavelength comprises operating the first source of illumination; and
the operating of the illumination system to provide the instance of strobed illumination of the second wavelength comprises operating the second source of illumination.

3. The method of claim 1 , further comprising providing a third wavelength image exposure contribution by operating the illumination system to provide an instance of strobed illumination of a third wavelength timed to correspond with a third phase timing of the periodically modulated focus position which compensates for longitudinal chromatic aberration of at least the variable focal length lens and focuses the third wavelength image exposure contribution at the first focus plane.

4. The method of claim 3 , wherein the first, second and third wavelengths correspond to three types of color detectors used in a color camera included in the imaging system.

5. The method of claim 3 , further comprising providing additional image exposure contributions by operating the illumination system to provide instances of strobed illumination of additional wavelengths timed to correspond with additional phase timings of the periodically modulated focus position which compensate for longitudinal chromatic aberration of at least the variable focal length lens and focus the additional wavelength image exposure contributions at the first focus plane.

6. The method of claim 1 , further comprising providing calibration data that at least in part:
relates phase timing of the periodically modulated focus position to a focus plane height or distance for the first wavelength; and
relates phase timing of the periodically modulated focus position to a focus plane height or distance for the second wavelength.

7. The method of claim 6 , wherein the second phase timing of the periodically modulated focus position which compensates for longitudinal chromatic aberration is determined based on at least a portion of the calibration data and at least one of the first phase timing or a height or distance of the first focus plane.

8. The method of claim 6 , wherein the providing of the calibration data comprises:
collecting a first image stack comprising respective images focused at respective Z-heights, wherein each image of the first image stack is exposed using an instance of strobed illumination of the first wavelength timed to correspond with a phase timing of the periodically modulated focus position corresponding to a Z-height within the image stack;
collecting a second image stack comprising respective images focused at respective Z-heights, wherein each image of the second image stack is exposed using an instance of strobed illumination of the second wavelength timed to correspond with a phase timing of the periodically modulated focus position corresponding to a Z-height within the image stack;
analyzing the first image stack to determine a first phase timing corresponding to a best focus position for a first region of interest at a first Z-height;
analyzing the second image stack to determine a second phase timing corresponding to a best focus position for the first region of interest at the first Z-height; and
storing as calibration data the first and second phase timings as associated with the first and second wavelengths, respectively, and as associated with the first the Z-height, wherein the first Z-height corresponds to the first focus plane.

9. The method of claim 8 , wherein the providing of the calibration data further comprises adjusting the height of the first region of interest through a plurality of Z-heights in addition to the first Z-height, and for each Z-height repeating the collecting and analyzing of the first and second image stacks and the storing of the phase timings as associated with the respective first and second wavelengths and as associated with the respective Z-height.

10. The method of claim 1 , wherein the second phase timing of the periodically modulated focus position which compensates for longitudinal chromatic aberration is determined based at least in part on:
at least one of the first phase timing, or a height or distance of the first focus plane that corresponds to the first phase timing; and
calibration data that relates the phase timing of the periodically modulated focus position to corresponding focus plane heights or distances for the second wavelength.

11. The method of claim 10 , wherein the calibration data is established during a learn mode which includes acquiring one or more image stacks and determining one or more focus peaks for the acquired one or more image stacks.

12. An image acquisition system, comprising:
an imaging system including a variable focal length lens that is utilized to periodically modulate a focus position of the imaging system over a plurality of focus positions along a Z-height direction;
an illumination system;
a memory for storing programmed instructions; and
a processor configured to execute the programmed instructions to perform operations including:
providing a first wavelength image exposure contribution by operating the illumination system to provide an instance of strobed illumination of a first wavelength timed to correspond with a first phase timing of the periodically modulated focus position which focuses the first wavelength image exposure contribution at a first focus plane;

providing a second wavelength image exposure contribution by operating the illumination system to provide an instance of strobed illumination of a second waveleng

Assignees

• Mitutoyo Corp

Inventors

• Bryll Robert Kamil
• Delaney Mark Lawrence

Classifications

• G02B21/365 Primary

  Control or image processing arrangements for digital or video microscopes (G02B21/361, G02B21/362 take precedence) · CPC title

• H04N23/672 Primary

  based on the phase difference signals · CPC title

• H04N25/611

  Correction of chromatic aberration · CPC title

• H04N23/12

  with one sensor only · CPC title

• H04N23/74

  by influencing the scene brightness using illuminating means · CPC title