Uniform filter to compensate for global inaccuracies using photometric stereo

A method comprising:

• using a camera to capture multiple images of a component, each image being lit by a different light source of a plurality of independently controllable light sources;
• applying photometric stereo to the multiple images to estimate surface height of each point along a surface of the component, relative to a horizontal line in each of the multiple images, the applying producing a first version of a two-dimensional height map indicating the surface height of each point along the surface of the component;
• blurring the first version of the two-dimensional height map using a blurring technique, producing a first blurred version of the two-dimensional height map;
• subtracting the first blurred version from the first version of the two-dimensional height map, resulting in a two-dimensional depth map of the surface;
• repeating the blurring and subtracting at least once using the depth map, producing a final version of the two-dimensional depth map;
• measuring change in depth of a feature of the surface of the component in the final version of the two-dimensional depth map;
• and
• using the change in depth of the feature to determine whether the feature is a defect in the component.

A non-transitory machine-readable storage medium having embodied thereon instructions executable by one or more machines to perform operations comprising:

• using a camera to capture multiple images of a component, each image being lit by a different light source of a plurality of independently controllable light sources;
• applying photometric stereo to the multiple images to estimate surface height of each point along a surface of the component, relative to a horizontal line in each of the multiple images, the applying producing a first version of a two-dimensional height map indicating the surface height of each point along the surface of the component;
• blurring the first version of the two-dimensional height map using a blurring technique, producing a first blurred version of the two-dimensional height map;
• subtracting the first blurred version from the first version of the two-dimensional height map, resulting in a two-dimensional depth map of the surface;
• repeating the blurring and subtracting at least once using the depth map, producing a final version of the two-dimensional depth map;
• measuring change in depth of a feature of the surface of the component in the final version of the two-dimensional depth map;
• and
• using the change in depth of the feature to determine whether the feature is a defect in the component.