The Junk Detector has been helpful to sort micrographs from a grid with irregular-sized holes, but it occasionally fails to detect the entire carbon area in a micrograph. Here are examples of one micrograph correctly marked, and two where the carbon area was partially marked.
This seems to be correlated with the percentage of area taken up by carbon. On micrographs with mostly ice, the carbon is detected reliably, whereas on micrographs with a large carbon area, it is not detected as consistently.