Points from focus operations using multiple light settings in a machine vision system

摘要

A method of automatically adjusting lighting conditions improves the results of points from focus (PFF) 3D reconstruction. Multiple lighting levels are automatically found based on brightness criteria and an image stack is taken at each lighting level. In some embodiments, the number of light levels and their respective light settings may be determined based on trial exposure images acquired at a single global focus height which is a best height for an entire region of interest, rather than the best focus height for just the darkest or brightest image pixels in a region of interest. The results of 3D reconstruction at each selected light level are combined using a Z-height quality metric. In one embodiment, the PFF data point Z-height value that is to be associated with an X-Y location is selected based on that PFF data point having the best corresponding Z-height quality metric value at that X-Y location.

主权项

1. A method for operating a precision machine vision inspection system to determine a set of multi-point Z-height measurement data comprising focus-based Z-height measurements in a particular region of interest on a workpiece, the precision machine vision inspection system comprising:
an imaging portion including a camera; a controllable lighting portion; a focusing portion; a control portion comprising an image processor; a first measuring mode for performing multi-point focus-based Z-height measurements on a workpiece, comprising operations that determine the multi-point focus-based Z-height measurements for a plurality of subregions within a region of interest based on a single image stack acquired using the same lighting parameters for each image in that image stack; a second measuring mode for performing multi-point focus-based Z-height measurements on a workpiece, comprising operations that determine the multi-point focus-based Z-height measurements for a plurality of subregions within a region of interest based on a plurality of image stacks, wherein a first image stack is acquired using darkness limiting lighting parameters that satisfy a darkness limiting criterion for image pixels in the region of interest and that are the same for each image in the first image stack, and a second image stack is acquired using brightness limiting lighting parameters that satisfy a brightness limiting criterion for image pixels in the region of interest and that are the same for each image in the second image stack; a user interface including an image display and a graphical user interface (GUI); and a multi-point Z-height measurement tool comprising:
the second measuring mode;the brightness limiting criterion for image pixels in the region of interest;the darkness limiting criterion for image pixels in the region of interest; anda multi-point GUI element including a region of interest indicator; andthe method comprising:
performing operations of the machine vision inspection system comprising:
acquiring an image of the particular region of interest on a workpiece;activating an instance of a multi-point Z-height measurement tool; anddefining a region of interest in the acquired image; performing automatic operations of that instance of the multi-point Z-height measurement tool corresponding to the second measuring mode, comprising:
(a) operations that automatically focus the imaging portion at a global best focus height for the region of interest, wherein the global best focus height is determined based on an image stack acquired using a preliminary set of lighting parameters and based on a focus metric that is determined based on the entire region of interest;(b) operations that analyze images acquired at the global best focus height and adjust the lighting parameters to determine brightness limiting lighting parameters that satisfy the brightness limiting criterion for image pixels in the region of interest, and(c) operations that analyze images acquired at the global best focus height and adjust the lighting parameters to determine darkness limiting lighting parameters that satisfy the darkness limiting criterion for image pixels in the region of interest.