Filters.h各种信号恢复滤波器头文件

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// ========================================================== // Upsampling / downsampling filters // // Design and implementation by // - Herv� Drolon ([e-mail]) // // This file is part of FreeImage 3 // // COVERED CODE IS PROVIDED UNDER THIS LICENSE ON AN "AS IS" BASIS, WITHOUT WARRANTY // OF ANY KIND, EITHER EXPRESSED OR IMPLIED, INCLUDING, WITHOUT LIMITATION, WARRANTIES // THAT THE COVERED CODE IS FREE OF DEFECTS, MERCHANTABLE, FIT FOR A PARTICULAR PURPOSE // OR NON-INFRINGING. THE ENTIRE RISK AS TO THE QUALITY AND PERFORMANCE OF THE COVERED // CODE IS WITH YOU. SHOULD ANY COVERED CODE PROVE DEFECTIVE IN ANY RESPECT, YOU (NOT // THE INITIAL DEVELOPER OR ANY OTHER CONTRIBUTOR) ASSUME THE COST OF ANY NECESSARY // SERVICING, REPAIR OR CORRECTION. THIS DISCLAIMER OF WARRANTY CONSTITUTES AN ESSENTIAL // PART OF THIS LICENSE. NO USE OF ANY COVERED CODE IS AUTHORIZED HEREUNDER EXCEPT UNDER // THIS DISCLAIMER. // // Use at your own risk! // ==========================================================  #ifndef _FILTERS_H_ #define _FILTERS_H_  /**  CGenericFilter is a generic abstract filter class used to access to the filter library.<br>  Filters used in this library have been mainly taken from the following references : <br> <b>Main reference</b> : <br> Paul Heckbert, C code to zoom raster images up or down, with nice filtering.  UC Berkeley, August 1989. [online] http://www-2.cs.cmu.edu/afs/cs.cmu.edu/Web/People/ph/heckbert.html  <b>Heckbert references</b> : <br> <ul> <li>Oppenheim A.V., Schafer R.W., Digital Signal Processing, Prentice-Hall, 1975 <li>Hamming R.W., Digital Filters, Prentice-Hall, Englewood Cliffs, NJ, 1983 <li>Pratt W.K., Digital Image Processing, John Wiley and Sons, 1978 <li>Hou H.S., Andrews H.C., "Cubic Splines for Image Interpolation and Digital Filtering",  IEEE Trans. Acoustics, Speech, and Signal Proc., vol. ASSP-26, no. 6, pp. 508-517, Dec. 1978. </ul>  */ class CGenericFilter { protected:      #define FILTER_PI  double (3.1415926535897932384626433832795)     #define FILTER_2PI double (2.0 * 3.1415926535897932384626433832795)     #define FILTER_4PI double (4.0 * 3.1415926535897932384626433832795)      /// Filter support double  m_dWidth;  public:          /// Constructor CGenericFilter (double dWidth) : m_dWidth (dWidth) {} /// Destructor     virtual ~CGenericFilter() {}      /// Returns the filter support double GetWidth()                   { return m_dWidth; } /// Change the filter suport     void   SetWidth (double dWidth)     { m_dWidth = dWidth; }      /// Returns F(dVal) where F is the filter's impulse response virtual double Filter (double dVal) = 0; };  // ----------------------------------------------------------------------------------- // Filters library // All filters are centered on 0 // -----------------------------------------------------------------------------------  /**  Box filter<br>  Box, pulse, Fourier window, 1st order (constant) b-spline.<br><br>   <b>Reference</b> : <br>  Glassner A.S., Principles of digital image synthesis. Morgan Kaufmann Publishers, Inc, San Francisco, Vol. 2, 1995 */ class CBoxFilter : public CGenericFilter { public:     /** Constructor<br> Default fixed width = 0.5 */     CBoxFilter() : CGenericFilter(0.5) {}     virtual ~CBoxFilter() {}      double Filter (double dVal) { return (fabs(dVal) <= m_dWidth ? 1.0 : 0.0); } };  /** Bilinear filter */ class CBilinearFilter : public CGenericFilter { public:      CBilinearFilter () : CGenericFilter(1) {}     virtual ~CBilinearFilter() {}      double Filter (double dVal) { dVal = fabs(dVal);  return (dVal < m_dWidth ? m_dWidth - dVal : 0.0);  } };   /**  Mitchell & Netravali's two-param cubic filter<br>   The parameters b and c can be used to adjust the properties of the cubic.   They are sometimes referred to as "blurring" and "ringing" respectively.   The default is b = 1/3 and c = 1/3, which were the values recommended by   Mitchell and Netravali as yielding the most visually pleasing results in subjective tests of human beings.   Larger values of b and c can produce interesting op-art effects--for example, try b = 0 and c = -5. <br><br>   <b>Reference</b> : <br>  Don P. Mitchell and Arun N. Netravali, Reconstruction filters in computer graphics.   In John Dill, editor, Computer Graphics (SIGGRAPH '88 Proceedings), Vol. 22, No. 4, August 1988, pp. 221-228. */ class CBicubicFilter : public CGenericFilter { protected: // data for parameterized Mitchell filter     double p0, p2, p3;     double q0, q1, q2, q3;  public:     /** Constructor<br> Default fixed width = 2 @param b Filter parameter (default value is 1/3) @param c Filter parameter (default value is 1/3) */     CBicubicFilter (double b = (1/(double)3), double c = (1/(double)3)) : CGenericFilter(2) { p0 = (6 - 2*b) / 6; p2 = (-18 + 12*b + 6*c) / 6; p3 = (12 - 9*b - 6*c) / 6; q0 = (8*b + 24*c) / 6; q1 = (-12*b - 48*c) / 6; q2 = (6*b + 30*c) / 6; q3 = (-b - 6*c) / 6; }     virtual ~CBicubicFilter() {}      double Filter(double dVal) {  dVal = fabs(dVal); if(dVal < 1) return (p0 + dVal*dVal*(p2 + dVal*p3)); if(dVal < 2) return (q0 + dVal*(q1 + dVal*(q2 + dVal*q3))); return 0; } };  /**  Catmull-Rom spline, Overhauser spline<br>   When using CBicubicFilter filters, you have to set parameters b and c such that <br>  b + 2 * c = 1<br>  in order to use the numerically most accurate filter.<br>  This gives for b = 0 the maximum value for c = 0.5, which is the Catmull-Rom   spline and a good suggestion for sharpness.<br><br>    <b>References</b> : <br>  <ul>  <li>Mitchell Don P., Netravali Arun N., Reconstruction filters in computer graphics.   In John Dill, editor, Computer Graphics (SIGGRAPH '88 Proceedings), Vol. 22, No. 4, August 1988, pp. 221-228.  <li>Keys R.G., Cubic Convolution Interpolation for Digital Image Processing.   IEEE Trans. Acoustics, Speech, and Signal Processing, vol. 29, no. 6, pp. 1153-1160, Dec. 1981.  </ul>  */ class CCatmullRomFilter : public CGenericFilter { public:      /** Constructor<br> Default fixed width = 2 */ CCatmullRomFilter() : CGenericFilter(2) {}     virtual ~CCatmullRomFilter() {}      double Filter(double dVal) {  if(dVal < -2) return 0; if(dVal < -1) return (0.5*(4 + dVal*(8 + dVal*(5 + dVal)))); if(dVal < 0)  return (0.5*(2 + dVal*dVal*(-5 - 3*dVal))); if(dVal < 1)  return (0.5*(2 + dVal*dVal*(-5 + 3*dVal))); if(dVal < 2)  return (0.5*(4 + dVal*(-8 + dVal*(5 - dVal)))); return 0; } };  /**  Lanczos-windowed sinc filter<br>    Lanczos3 filter is an alternative to CBicubicFilter with high values of c about 0.6 ... 0.75   which produces quite strong sharpening. It usually offers better quality (fewer artifacts) and a sharp image.<br><br>  */ class CLanczos3Filter : public CGenericFilter { public:     /** Constructor<br> Default fixed width = 3 */ CLanczos3Filter() : CGenericFilter(3) {}     virtual ~CLanczos3Filter() {}      double Filter(double dVal) {  dVal = fabs(dVal);  if(dVal < m_dWidth){ return (sinc(dVal) * sinc(dVal / m_dWidth)); } return 0; }  private: double sinc(double value) { if(value != 0) { value *= FILTER_PI; return (sin(value) / value); }  return 1; } };  /**  4th order (cubic) b-spline<br>  */ class CBSplineFilter : public CGenericFilter { public:      /** Constructor<br> Default fixed width = 2 */ CBSplineFilter() : CGenericFilter(2) {}     virtual ~CBSplineFilter() {}      double Filter(double dVal) {   dVal = fabs(dVal); if(dVal < 1) return (4 + dVal*dVal*(-6 + 3*dVal)) / 6; if(dVal < 2) { double t = 2 - dVal; return (t*t*t / 6); } return 0; } };  // ----------------------------------------------------------------------------------- // Window function library // -----------------------------------------------------------------------------------  /**   Blackman window */ class CBlackmanFilter : public CGenericFilter { public:     /** Constructor<br> Default width = 0.5 */     CBlackmanFilter (double dWidth = double(0.5)) : CGenericFilter(dWidth) {}     virtual ~CBlackmanFilter() {}      double Filter (double dVal) { if(fabs (dVal) > m_dWidth) { return 0;          }         double dN = 2 * m_dWidth + 1;  dVal /= (dN - 1);         return 0.42 + 0.5*cos(FILTER_2PI*dVal) + 0.08*cos(FILTER_4PI*dVal);      } };  #endif  // _FILTERS_H_