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S S08 D I P Lec07 Pixel Operations

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S S08 D I P Lec07 Pixel Operations

1. 1. Pixel Processing SS 2008 – Image Processing Multimedia Computing, Universität Augsburg Rainer.Lienhart@informatik.uni-augsburg.de www.multimedia-computing.{de,org}
2. 2. Reference Bernd Jähne. Digital Image Processing. Springer Verlag. Chapter on Pixel Processing (chap 8 in 4th edition) Most Figures are taken from that book © 2005-2008 Prof. Dr. R. Lienhart, Head of Multimedia Computing, Institut für Informatik, Universität Augsburg 2 Eichleitnerstr. 30, D-86135 Augsburg, Germany; email: Rainer.Lienhart@informatik.uni-augsburg.de
3. 3. Point Operations := modification of gray value at individual pixels dependent only on the gray value and possibly on the position of the pixel I ' ( x, y)  Px, y I ( x, y) © 2005-2008 Prof. Dr. R. Lienhart, Head of Multimedia Computing, Institut für Informatik, Universität Augsburg 3 Eichleitnerstr. 30, D-86135 Augsburg, Germany; email: Rainer.Lienhart@informatik.uni-augsburg.de
4. 4. Homogeneous Point Operations := Point operation independent of position of pixel I ' ( x, y)  PI ( x, y) • Map set of gray values onto itself • Generally not invertible: – Example: Thresholding  0 q  threshold P(q)   255 q  threshold  Not invertible – Example: Invertion Pnegation(q)  255  q , q  I ( x, y)  Invertible © 2005-2008 Prof. Dr. R. Lienhart, Head of Multimedia Computing, Institut für Informatik, Universität Augsburg 4 Eichleitnerstr. 30, D-86135 Augsburg, Germany; email: Rainer.Lienhart@informatik.uni-augsburg.de
5. 5. Image Thresholding Two principles • Fixed threshold; • Adaptive threshold; void cvThreshold( const CvArr* src, CvArr* dst, double threshold, double max_value, int threshold_type ); src = Source array (single-channel, 8-bit of 32-bit floating point). dst = Destination array; must be either the same type as src or 8-bit. threshold = threshold value. max_value = Maximum value to use with CV_THRESH_BINARY and CV_THRESH_BINARY_INV thresholding types. threshold_type = Thresholding type (see the discussion) © 2005-2008 Prof. Dr. R. Lienhart, Head of Multimedia Computing, Institut für Informatik, Universität Augsburg 5 Eichleitnerstr. 30, D-86135 Augsburg, Germany; email: Rainer.Lienhart@informatik.uni-augsburg.de