Investigation of basic imaging properties in digital radiography. 4. Effect of unsharp masking on the detectability of simple patterns

Authors:
  • LLLeh‐Nien D. Loo
    Leh‐Nien D. Loo
  • KDKunio Doi
    Kunio Doi
  • CMCharles E. Metz
    Charles E. Metz
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Abstract
The signal‐to‐noise ratios (SNRs) of simple radiologic patterns processed by the unsharp‐masking technique were calculated on the basis of a statistical decision theory model that includes both the observer's visual transfer function and a noise component internal to his eye–brain system. For a variety of processing parameters, the contrast‐detail diagrams predicted from this SNR agreed qualitatively with experimental results obtained in observer performance studies. Unsharp masking with a large mask and a large weighting factor improved the detection of square objects to a level comparable with that achieved by the overall contrast enhancement technique using a factor of 4. However, unsharp masking with a small mask and a large weighting factor can substantially degrade the detectability of these objects. The potential practical utility of the unsharp‐masking technique is discussed.