Method for Focus Control

• US 20090310011A1
• Filed: 12/08/2006
• Published: 12/17/2009
• Est. Priority Date: 12/19/2005
• Status: Active Grant

• Current Assignee: British Telecommunications PLC (BT Group PLC)
• Original Assignee: British Telecommunications PLC (BT Group PLC)
• Inventors: Stentiford, Frederick W. M., Shilston, Robert T.
• Granted Patent: US 8,040,428 B2
• Time in Patent Office: Days
• US Class Current: 348/345
• CPC Class Codes: G02B 7/38 measured at different points on the optical axis , e.g. focussing on two or more planes and comparing image data
• CPC Class Codes: H04N 23/676 Bracketing for image capture at varying focusing conditions

Abstract

A camera or other optical system is focused by generating a plurality of digital images each obtained with a different focus setting of the optical system. These images are analysed to generate for each image a score (S) by comparing first groups of pixels chosen from the image with second groups chosen from the image such that the pixels of each second group have same respective positional relationships with respect to one another as the pixels of the first group with which it is compared have to one another, the score (S) being a function of the number of matches obtained with said comparisons. The focus setting that gives the score corresponding to the largest number of matches is chosen.

Claims

1. A method of focusing an optical system, comprising:

(a) generating a plurality of digital images each obtained with a different focus setting of the optical system within a desired focusing range;

(b) analysing the digital images to generate for each image a score (S) by comparing first groups of pixels chosen from the image and having randomly chosen positional relationships with respect to one another with randomly positioned second groups chosen from the image such that the pixels of each second group have the same respective positional relationships with respect to one another as the pixels of the first group with which it is compared have to one another, the score (S) being a function of the number of mismatches obtained with said comparisons;

choosing that focus setting that corresponds to a score indicative of the largest number of mismatches.

2. A method according to claim 1 in which each score is generated by:

storing each image as an array of pixels, each pixel having a value;

selecting test pixels from the array,

for each test pixel,

selecting one or more neighbour groups of pixels neighbouring the test pixel;

selecting comparison pixels from the array;

identifying a group of pixels neighbouring a selected comparison pixel having the same respective positional relationships to the comparison pixel as a selected neighbour group of pixels has to the test pixel; and

comparing the values of the selected neighbour group with the values of the identified group in accordance with a predetermined match criterion, and

generating the score for the image, in dependence upon the number of comparisons for which the comparison results in a mismatch.