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Marker characteristics


A marker's characteristics are its identifying qualities, such as its search region and polarity. The more precisely you define a marker's characteristics, the more likely MmeasFindMarker() will find the marker you want.

To locate markers, the find operation uses two phases, each of which validates a specific set of characteristics:

  • Phase one, which validates essential characteristics, set using MmeasSetMarker().

  • Phase two, which validates score characteristics, set using MmeasSetScore().

MmeasSetMarker() has essential characteristic settings that you should consider both basic (you typically change them) and advanced (you rarely change them), while MmeasSetScore() should be considered entirely advanced.

Essential characteristics

During the first phase of the search, MIL locates markers based on whether they have all the essential characteristics, as specified with MmeasSetMarker(). MIL considers every characteristic set with MmeasSetMarker() an unconditional requirement and discards any marker that does not have all of them. For example, a marker that does not have the specified polarity characteristic (M_POLARITY) can never be found, regardless of any other setting.

Marker characteristics are set to their default upon the allocation of the marker buffer (MmeasAllocMarker()). Typically, essential characteristics other than the search region's origin or center can be set to M_ANY if the value is unknown or not a criteria. M_ANY generally indicates that you want to ignore that characteristic. Markers that have all the essential characteristics move on to phase two.

Score characteristics

During the second phase of the search, MIL calculates a score for each marker characteristic specified with MmeasSetScore(), and the marker with the highest score is found. Unlike essential characteristics, which are either met or not, MmeasSetScore() allows you to specify a range of acceptability, resulting in a characteristic score based on how well the calculated characteristic falls within that range. For example, you can specify that markers with a higher contrast score are better than markers with a lower contrast (M_EDGE_CONTRAST_SCORE), this allows you to find the marker with the best contrast while at the same time not eliminating markers with lower contrasts. For more information, see the Score characteristics section later in this chapter.

If you do not specify any score characteristic, MIL only considers the marker's edge strength (M_STRENGTH_SCORE). Therefore, the marker with the strongest edges (highest edgevalues), and with all the essential characteristics, is found by default. This behavior is typically sufficient for most cases, and you need not call MmeasSetScore(). However, in advanced applications, or when you must distinguish between similar markers, score characteristics can prove useful to fine tune your search.