Using Moiré Chroma for DSC On-line Focus Calibration

Focus is an important part before capturing an image by DSC. After obtaining an optimized focus, image can have best contrast to evaluate. So far, many focus methods were built and they include maximum contrast search and object distance inverse calculation. No mater which method is used, both can provide us best focus to capture. In this paper, another method to determine focus is moiré. Reason of moiré happened is related to sensor’s pixel pitch and spatial frequency of capture target. When moiré happened and based on mosaic CFA (Color Filter Array), the captured image will result in special slanted line and some colored pixel. In some focus test, moiré was known to be a method to determine focus, but it is inspected by human visual without any quantification. This paper tries to use chroma of moiré to make some experiment and to compare with contrast method. Therefore, focus can be determined simply by chroma calculation