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emboss.cpp

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00001 //==============================================
00002 //  copyright            : (C) 2003-2005 by Will Stokes
00003 //==============================================
00004 //  This program is free software; you can redistribute it
00005 //  and/or modify it under the terms of the GNU General
00006 //  Public License as published by the Free Software
00007 //  Foundation; either version 2 of the License, or
00008 //  (at your option) any later version.
00009 //==============================================
00010 
00011 //Systemwide includes
00012 #include <qimage.h>
00013 #include <qstring.h>
00014 #include <qapplication.h>
00015 #include <math.h>
00016 
00017 //Projectwide includes
00018 #include "emboss.h"
00019 #include "../tools/imageTools.h"
00020 #include "../../gui/statusWidget.h"
00021 
00022 //----------------------------------------------
00023 // Inputs:
00024 // -------
00025 // QString filename - location of original image on disk
00026 // StatusWidget* status - widget for making progress visible to user
00027 //
00028 // Outputs:
00029 // --------
00030 // QImage* returned - constructed image
00031 //
00032 // Description:
00033 // ------------
00034 // This method constructs an embossed version of
00035 // the image by modifying the luminance of each pixel
00036 // by taking a weighted average of pixel luminance within
00037 // a local neighborhood. Most embossing algorithms convert an 
00038 // image to grayscale and then combine a pixel's gray value with
00039 // its neighbors using the following convolution matrix:
00040 //
00041 // [ -1  -1   0
00042 //   -1   1   1
00043 //    0   1   1 ]
00044 //
00045 // This apporach has two problems. First, all color information
00046 // is lost. Second, the convolution filter is not a function of image
00047 // size, and as a result embossing results on high resolution images are
00048 // barely when viewed on a high resolution screen or printed at high DPI. 
00049 // 
00050 // My solution to this problem is to:
00051 //
00052 // 1.) Apply the emboss effect on pixel luminance and leave pixel
00053 // color untouched. The varying lightness that results produces
00054 // the same effect, and if a grayscale image is really desired the
00055 // image can be converted to grayscale either before or after the 
00056 // emboss effect takes place.
00057 // 
00058 // 2.) using neighboring pixels that are a distance D from the 
00059 // pixel being modified in the X or Y dimensions. This simply 
00060 // modification allows the embossing procedure to run at the 
00061 // same speed (larger convolution matrices would slow the algorithm 
00062 // to at best O(N^2 * M^2) where there are N^2 pixels in the image 
00063 // and the convolution matrix is M^2 in size) while providing the 
00064 // same effective emboss effect at any image resolution. This is 
00065 // done by computing distance D using the minimum image dimension:
00066 //
00067 // D = MIN( width, height )
00068 //
00069 // At each pixel, we compute an average luminance of the 6 
00070 // neighbors and combine these values with a 50% luminance value for 
00071 // the pixel in question. This luminance value is used to replace 
00072 // the current pixel luminance before converting it back to RGB 
00073 // space and storing in the edited image object.
00074 //
00075 // Neighbor pixels that are clamped to be on the image plane to 
00076 // prevent lookups of neighbor pixels with negative coordinates or
00077 // coordinates beyond the width/height of the image in question.
00078 //----------------------------------------------
00079 
00080 //==============================================
00081 QImage* embossEffect( QString filename, StatusWidget* status )
00082 {
00083   //load original image  
00084   QImage originalImage( filename );
00085 
00086   //create edited image
00087   QImage* editedImage = new QImage( filename );
00088   
00089   //determine if busy indicators will be used
00090   bool useBusyIndicators = (status != NULL);
00091   
00092   //setup progress bar
00093   if(useBusyIndicators)
00094   {
00095     QString statusMessage = qApp->translate( "embossEffect", "Applying Emboss Effect:" );
00096     status->showProgressBar( statusMessage, 100 );
00097     qApp->processEvents();  
00098   }
00099   
00100   //update progress bar for every 1% of completion
00101   const int updateIncrement = (int) ( 0.01 * originalImage.width() * originalImage.height() );
00102   int newProgress = 0; 
00103 
00104   //iterate over each selected scanline 
00105   int x, y;
00106   QRgb* rgb;
00107   uchar* scanLine;
00108 
00109   int yPrev, yNext, xPrev, xNext;
00110   
00111   //compute the radius using image resolution
00112   double minDimen = (double) QMIN( editedImage->width(), editedImage->height() );  
00113   const int embossRadius = (int) QMAX( 1, (sqrt(minDimen)/8) );
00114   
00115   for( y=0; y<editedImage->height(); y++)
00116   {   
00117     scanLine = originalImage.scanLine(y);
00118 
00119     //compute previous and next y pixel coordinates
00120     yPrev = QMAX( y-embossRadius, 0 );
00121     yNext = QMIN( y+embossRadius, editedImage->height() - 1 );
00122     
00123     //iterate over each selected pixel in scanline
00124     for( x=0; x<editedImage->width(); x++)
00125     {
00126       //compute previous and next x  pixel coordinates
00127       xPrev = QMAX( x-embossRadius, 0 );
00128       xNext = QMIN( x+embossRadius, editedImage->width() - 1 );
00129 
00130       //start with a default luminance of 128 (50% luminance)
00131       int sum = 128;
00132       
00133       //sum weighted gray values of neighbors
00134       scanLine = originalImage.scanLine( yPrev );
00135       sum-= qGray( *((QRgb*)scanLine + xPrev ) );
00136       sum-= qGray( *((QRgb*)scanLine + x ) );
00137 
00138       scanLine = originalImage.scanLine( y );
00139       sum-= qGray( *((QRgb*)scanLine + xPrev ) );
00140       sum+= qGray( *((QRgb*)scanLine + xNext ) );
00141 
00142       scanLine = originalImage.scanLine( yNext );
00143       sum+= qGray( *((QRgb*)scanLine + x ) );
00144       sum+= qGray( *((QRgb*)scanLine + xNext ) );
00145       
00146       //clamp sum to within 0-255 range
00147       sum = QMAX( QMIN( sum, 255), 0 );
00148 
00149       //get original pixel color in HSV space
00150       scanLine = editedImage->scanLine(y);            
00151       rgb = ((QRgb*)scanLine+x);
00152       double r = ((double)qRed(*rgb)   )/255.0;
00153       double g = ((double)qGreen(*rgb) )/255.0;
00154       double b = ((double)qBlue(*rgb)  )/255.0;
00155       
00156       //convert to hsv
00157       double h,s,v;
00158       RGBtoHSV(r,g,b,&h,&s,&v);
00159       
00160       //reset v
00161       v = ((double)sum)/255;
00162       
00163       //convert adjusted color back to rgb colorspace and clamp
00164       HSVtoRGB( &r,&g,&b, h,s,v);         
00165       int rp = (int) QMIN( QMAX((r*255), 0), 255 );
00166       int gp = (int) QMIN( QMAX((g*255), 0), 255 );
00167       int bp = (int) QMIN( QMAX((b*255), 0), 255 );
00168       
00169       //set adjusted color value
00170       *rgb = qRgb(rp,gp,bp);
00171       
00172       //update status bar if significant progress has been made since last update
00173       if(useBusyIndicators)
00174       {
00175         newProgress++;
00176         if(newProgress >= updateIncrement)
00177         {
00178           newProgress = 0;
00179           status->incrementProgress();
00180           qApp->processEvents();  
00181         }
00182       }
00183       
00184     }
00185   }
00186   
00187   //return pointer to edited image
00188   return editedImage;  
00189 }
00190 //==============================================

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