blackWhite.cpp

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//==============================================
//  copyright            : (C) 2003-2005 by Will Stokes
//==============================================
//  This program is free software; you can redistribute it
//  and/or modify it under the terms of the GNU General
//  Public License as published by the Free Software
//  Foundation; either version 2 of the License, or
//  (at your option) any later version.
//==============================================
 
//Systemwide includes
#include <qimage.h>
#include <qstring.h>
#include <qapplication.h>
 
//Projectwide includes
#include "blackWhite.h"
#include "manipulationOptions.h"
#include "../../gui/statusWidget.h"
 
//----------------------------------------------
// Inputs:
// -------
// QString filename - location of original image on disk
// StatusWidget* status - widget for making progress visible to user
//
// Outputs:
// --------
// QImage* returned - constructed image
//
// Description:
// ------------
// This method constructs a grayscale version of
// the image by computing a gray value for each pixel. A naive
// approach would use the average the red, green, and blue components
// at each pixel for the new pixel component values, that is:
//
// gray = (r+g+b) / 3;
// r' = gray; g' = gray; b'= gray
//
// The problem with this approach is that image luminance 
// (observed brightness) is not maintained. Instead, we conpute
// the brightness at each pixel using a weighted sum of the color
// components. Weights vary depending on display device.
// Old school NTSC TV's which came out in the 50's would
// tell us to use these r,b,g weights (which Gimp uses):
// (see http://www.gimp.org/tutorials/Color2BW)
// (0.3, 0.59, 0.11)
//
// But these days we're using modern monitors and the green phosphur 
// is brigther or something so it's best to use these instead:
// http://lists.trolltech.com/qt-interest/1999-10/thread00337-0.html
// (0.2125, 0.7154, 0.0721)
//
// After weighting, the resulting gray value is clamped to fall within the 
// [0-255] range and assigned to the pixel in the new image.
//----------------------------------------------
 
//==============================================
QImage* blackWhiteEffect( QString filename, ManipulationOptions* options )
{
  //load image
  QImage* editedImage = new QImage( filename );
  
  //convert to 32-bit depth if necessary
  if( editedImage->depth() < 32 )
  {
    QImage* tmp = editedImage;
    editedImage = new QImage( tmp->convertDepth( 32, Qt::AutoColor ) );
    delete tmp; tmp=NULL;
  }
  
  //determine if busy indicators will be used
  bool useBusyIndicators = false;
  StatusWidget* status = NULL;
  if( options != NULL && options->getStatus() != NULL )
  {
    useBusyIndicators = true;
    status = options->getStatus(); 
  }
  
  //setup progress bar
  if(useBusyIndicators)
  {
    QString statusMessage = qApp->translate( "blackWhiteEffect", "Applying Black + White Effect:" );
    status->showProgressBar( statusMessage, 100 );
    qApp->processEvents();  
  }
  
  //update progress bar for every 1% of completion
  const int updateIncrement = (int) ( 0.01 * editedImage->width() * editedImage->height() );
  int newProgress = 0; 
 
  //iterate over each selected scanline 
  int x, y, grayValue;
  QRgb* rgb;
  uchar* scanLine;
  for( y=0; y<editedImage->height(); y++)
  {   
    //iterate over each selected pixel in scanline
    scanLine = editedImage->scanLine(y);
    for( x=0; x<editedImage->width(); x++)
    {
      //compute gray value based on the display luminance of color coordinates
      rgb = ((QRgb*)scanLine+x);
      grayValue = (int) (0.2125*qRed(*rgb) + 0.7154*qGreen(*rgb) + 0.0721*qBlue(*rgb));
      
      //clamp to ensure it falls in the 0-255 range
      grayValue = QMIN( QMAX( grayValue, 0 ), 255 );      
      
      //set pixel channel values using computed gray value
      *rgb = qRgb( grayValue, grayValue, grayValue );      
 
      //update status bar if significant progress has been made since last update
      if(useBusyIndicators)
      {
        newProgress++;
        if(newProgress >= updateIncrement)
        {
          newProgress = 0;
          status->incrementProgress();
          qApp->processEvents();  
        }
      }
 
    }
  }
   
  //return pointer to edited image
  return editedImage;  
}
//==============================================