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90 lines
3.4 KiB
ReStructuredText
90 lines
3.4 KiB
ReStructuredText
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Histograms
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==========
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.. highlight:: cpp
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CalcPGH
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-------
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Calculates a pair-wise geometrical histogram for a contour.
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.. ocv:cfunction:: void cvCalcPGH( const CvSeq* contour, CvHistogram* hist )
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:param contour: Input contour. Currently, only integer point coordinates are allowed.
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:param hist: Calculated histogram. It must be two-dimensional.
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The function calculates a 2D pair-wise geometrical histogram (PGH), described in [Iivarinen97]_ for the contour. The algorithm considers every pair of contour
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edges. The angle between the edges and the minimum/maximum distances
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are determined for every pair. To do this, each of the edges in turn
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is taken as the base, while the function loops through all the other
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edges. When the base edge and any other edge are considered, the minimum
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and maximum distances from the points on the non-base edge and line of
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the base edge are selected. The angle between the edges defines the row
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of the histogram in which all the bins that correspond to the distance
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between the calculated minimum and maximum distances are incremented
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(that is, the histogram is transposed relatively to the definition in the original paper). The histogram can be used for contour matching.
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.. [Iivarinen97] Jukka Iivarinen, Markus Peura, Jaakko Srel, and Ari Visa. *Comparison of Combined Shape Descriptors for Irregular Objects*, 8th British Machine Vision Conference, BMVC'97. http://www.cis.hut.fi/research/IA/paper/publications/bmvc97/bmvc97.html
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QueryHistValue*D
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----------------
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Queries the value of the histogram bin.
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.. ocv:cfunction:: float cvQueryHistValue_1D(CvHistogram hist, int idx0)
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.. ocv:cfunction:: float cvQueryHistValue_2D(CvHistogram hist, int idx0, int idx1)
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.. ocv:cfunction:: float cvQueryHistValue_3D(CvHistogram hist, int idx0, int idx1, int idx2)
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.. ocv:cfunction:: float cvQueryHistValue_nD(CvHistogram hist, const int* idx)
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:param hist: Histogram.
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:param idx0: 0-th index.
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:param idx1: 1-st index.
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:param idx2: 2-nd index.
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:param idx: Array of indices.
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The macros return the value of the specified bin of the 1D, 2D, 3D, or N-D histogram. In case of a sparse histogram, the function returns 0. If the bin is not present in the histogram, no new bin is created.
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GetHistValue\_?D
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----------------
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Returns a pointer to the histogram bin.
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.. ocv:cfunction:: float cvGetHistValue_1D(CvHistogram hist, int idx0)
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.. ocv:cfunction:: float cvGetHistValue_2D(CvHistogram hist, int idx0, int idx1)
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.. ocv:cfunction:: float cvGetHistValue_3D(CvHistogram hist, int idx0, int idx1, int idx2)
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.. ocv:cfunction:: float cvGetHistValue_nD(CvHistogram hist, int idx)
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:param hist: Histogram.
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:param idx0: 0-th index.
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:param idx1: 1-st index.
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:param idx2: 2-nd index.
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:param idx: Array of indices.
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::
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#define cvGetHistValue_1D( hist, idx0 )
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((float*)(cvPtr1D( (hist)->bins, (idx0), 0 ))
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#define cvGetHistValue_2D( hist, idx0, idx1 )
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((float*)(cvPtr2D( (hist)->bins, (idx0), (idx1), 0 )))
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#define cvGetHistValue_3D( hist, idx0, idx1, idx2 )
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((float*)(cvPtr3D( (hist)->bins, (idx0), (idx1), (idx2), 0 )))
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#define cvGetHistValue_nD( hist, idx )
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((float*)(cvPtrND( (hist)->bins, (idx), 0 )))
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..
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The macros ``GetHistValue`` return a pointer to the specified bin of the 1D, 2D, 3D, or N-D histogram. In case of a sparse histogram, the function creates a new bin and sets it to 0, unless it exists already.
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