Method of and apparatus for the expansion of the range of the depth of focus beyond the limit given by conventional images

• US 4,141,032 A
• Filed: 06/09/1977
• Issued: 02/20/1979
• Est. Priority Date: 12/08/1976
• Status: Expired due to Term

• Current Assignee: Ernst Leitz Wetzlar GmbH (ACM Project Development Co.)
• Original Assignee: Ernst Leitz Wetzlar GmbH (ACM Project Development Co.)
• Inventors: Haeusler, Gerd
• Primary Examiner(s): Murray, Richard
• Application Number:
  US05/805,159
• Time in Patent Office: 621 Days
• Field of Search: 358/89, 358/88, 358/160, 358/209, 358/225
• US Class Current: 348/44
• CPC Class Codes: G02B 21/006 focusing arrangements; selection of the plane to be imaged
• CPC Class Codes: G02B 21/008 Details of detection or image processing, including general computer control
• CPC Class Codes: G02B 21/24 Base structure
• CPC Class Codes: G02B 21/241 Devices for focusing focusing in general G02B7/28
• CPC Class Codes: H04N 23/81 for suppressing or minimising disturbance in the image signal generation

Abstract

A method of and apparatus for increasing the range of depth of focus when optically imaging three dimensional objects having different depth ranges corresponding to desired image levels wherein the object is focused through at a plurality of levels to produce a plurality of images. At each level, the image produced has sharp details and unfocused details. Each image is filtered with a high pass filter to suppress unfocused details and to pass sharp details. The images are then summed to produce a composite image containing only the sharp details passed by the filtering step. If desired, the filter may be selectively by-passed in order to sum unfiltered images. By utilizing the method of an apparatus for practicing the instant invention more meaningful visual displays of three-dimensional objects are obtained.

Claims

1. A method for increasing the range of depths of focus when optically imaging three dimensional objects having different depth ranges corresponding to desired image levels comprising the steps of:

focusing through the object at a plurality of levels to produce a plurality of images wherein each image has sharp details and unfocused details;

converting each image to an electrical signal pattern;

filtering each electrical signal pattern to suppress unfocused details and to pass a filtered electrical signal pattern including only substantially sharp details; and

summing the filtered electrical signal patterns to produce a composite electrical signal pattern representing a composite image containing only the sharp details passed by the filtering step.

2. The method of claim 1 wherein the filtering step is performed through a high pass filter and includes the step of increasing the frequency response of the filter for each image filtered.

3. The method of claim 2 wherein the frequency response is increased linearly.

4. The method of claim 2 wherein the frequency response follows an inverse of an integrated transfer function in order to restore the transfer function exactly.

5. The method of claim 1 further including the step of blending the filtered electrical signal pattern with the unfiltered signal pattern by bypassing the filtering step selectively according to a selected ratio and by summing the filtered and unfiltered electrical signal patterns.

6. The method of claim 1 wherein the focusing step for each image level includes focusing in a series of steps wherein for each step the focus is partially clear to thereby produce a plurality of partially clear images which are converted to an electrical signal pattern and summed to produce an electrical signal pattern which is representative of the image for that level.

7. The method of claim 1 wherein the step of converting each image to an electrical signal pattern is accomplished with a video camera and wherein the electrical signal patterns are video signals.

8. The method of claim 7 further comprising the steps of storing the video signals after they are summed and displaying the stored video signals.

9. An apparatus for increasing the range of depths of focus when optically imaging a three-dimensional object having different depth ranges corresponding to desired image levels, said apparatus comprising:

objective means for focusing through the object;

means for moving the object and objective means relative to one another to bring selected levels of the object into sharp focus;

means for producing images of the object as the object appears at said selected levels;

means for converting the images to electrical signal patterns;

means for filtering the electrical signal patterns wherein said filtering means includes a high pass filter which suppresses portions of the electrical signal patterns representing unfocused details of the images and passes portions of the electrical signal patterns representing sharp details to produce filtered electrical signal patterns; and

means for summing the filtered electrical signal pattern to produce a composite electrical signal pattern which represents a composite image clearly portraying the three dimensional object.

10. The apparatus of claim 9 further including bypass means for bypassing said filter to apply an unfiltered electrical signal pattern to said summing means which is summed with an electrical signal pattern representing a filtered image.

11. The apparatus of claim 9 further including storage means for storing an electrical signal pattern representing each image as that electrical signal pattern is filtered.

12. The apparatus of claim 11 wherein the means for converting the images to electrical signal patterns is a video camera.

13. The apparatus of claim 12 wherein the storage means is a video signal storage device.

14. The apparatus of claim 13 further including a video monitor for displaying the images stored in said storage means.