trans_graph.C File Reference

Detailed Description

Demonstrates how to access and manipulate ARGB pixel values of an image +...

• how to make a part of an image to be transparent.
• how to merge/alphablend an image with transparent colors with some background image.

Processing /mnt/build/workspace/root-makedoc-v610/rootspi/rdoc/src/v6-10-00-patches/tutorials/image/trans_graph.C...
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 i 6 0.600000 7.173561 
 i 7 0.700000 7.833269 
 i 8 0.800000 8.414710 
 i 9 0.900000 8.912074 
 i 10 1.000000 9.320391 
 i 11 1.100000 9.635582 
 i 12 1.200000 9.854497 
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 i 15 1.500000 9.916648 
 i 16 1.600000 9.738476 
 i 17 1.700000 9.463001 
 i 18 1.800000 9.092974 
 i 19 1.900000 8.632094 
*************** File trans_graph.png created ***************

#include "TColor.h"
#include "TImage.h"
#include "TImageDump.h"
#include "TVirtualPad.h"
#include "TROOT.h"
#include "TFrame.h"

UInt_t color2rgb(TColor *col)
{
   // returns RGB value of color

   return ((UInt_t(col->GetRed()*255) << 16) +
           (UInt_t(col->GetGreen()*255) << 8) +
            UInt_t(col->GetBlue()*255));
}


void trans_graph()
{
   // remember if  we are in batch mode
   Bool_t batch = gROOT->IsBatch();

   // switch to batch mode
   gROOT->SetBatch(kTRUE);

   // execute graph.C macro
   gROOT->Macro("$ROOTSYS/tutorials/graphs/graph.C");

   // create gVirtualPS object
   TImageDump dmp("dummy.png");
   TImage *fore = dmp.GetImage();  // image associated with image_dump

   // resize canvas
   gPad->SetCanvasSize(400, 300);
   gPad->Paint(); // paint gPad on fore image associated with TImageDump

   // open background image
   TImage *back = TImage::Open("$ROOTSYS/tutorials/image/rose512.jpg");

   // choose colors to be transparent
   TColor *bk1 = gROOT->GetColor(gPad->GetFillColor());
   TColor *bk2 = gROOT->GetColor(gPad->GetFrame()->GetFillColor());
   UInt_t rgb1 = color2rgb(bk1);
   UInt_t rgb2 = color2rgb(bk2);

   // get directly accessible ARGB array
   UInt_t *argb = fore->GetArgbArray();
   UInt_t w = fore->GetWidth();
   UInt_t h = fore->GetHeight();

   // scan all pixels in fore image and
   // make rgb1, rgb2 colors transparent.
   for (UInt_t i = 0; i < h; i++) {
      for (UInt_t j = 0; j < w; j++) {
         Int_t idx = i*w + j;

         // RGB part of ARGB color
         UInt_t col = argb[idx] & 0xffffff;

         // 24..31 bits define transparency of the color in the range 0 - 0xff
         // for example, 0x00000000 - black color with 100% transparency
         //              0xff000000 - non-transparent black color

         if ((col == rgb1) || (col == rgb2)) { //
            argb[idx] = 0; // 100% transparent
         } else {
            argb[idx] = 0xff000000 + col;  // make other pixels non-transparent
         }
      }
   }

   // alphablend back and fore images
   back->Merge(fore, "alphablend", 20, 20);

   // write result image in PNG format
   back->WriteImage("trans_graph.png");
   printf("*************** File trans_graph.png created ***************\n");

   delete back;

   // switch back to GUI mode
   if (!batch) gROOT->SetBatch(kFALSE);
}

Author

Valeriy Onuchin

Definition in file trans_graph.C.