Quality metric that is computed from the average of all the pixels in the diffraction pattern. The pixels with a value of zero are ignored, so that the pixels removed from the Mask disc operation are ignored.
where W is the width of the pattern, H is the height of the pattern and the pixel value at position (i, j).
This quality index was used by Wright and Nowell . They summarized this quality index as:
- a measure of the overall backscatter yield
- related to surface topography
- show scratches, microtwins and small strain levels
- affected by contamination, gain, contrast settings and current drift