Patent ID: 8705837
Filing Date: 2014-04-22
Classification: G01N,G06F,G06T

Abstract:
1. A method for inspecting and detecting defects on surfaces of disc-shaped objects, comprising the following steps: capturing an image of the respective disc-shaped object, wherein the entire surface is captured with a plurality of fields; deriving a defect-free reference of a pre-defined size from plural fields equal in size on the surface of the disc-shaped object; generating a difference image of the surface of the disc-shaped object, wherein the derived reference is subtracted from each field on the surface of the disc-shaped object; applying a color transformation to the difference image, wherein, by a suitable choice of transformation, signals in one channel are maximized, while undesired variations of the fields, caused by the production, are moved to a different channel; evaluating the signals, wherein a mean value, a variance, a maximum value and a minimum value are determined for each field; determining a distribution of the signals for each pixel of a field and a distribution of the signals for each defect to be examined, wherein the distribution is determined for each combination of transformation and detection channel used; and selecting that combination of transformation and detection channel, for which the largest number of pixels of a field with the defect to be found lie outside the spread of the pixels of the respective field on the surface of the respective disc-shaped object from production, and which results in the largest signals for the defect.