TASImage image("$ROOTSYS/tutorials/visualisation/image/rose512.jpg");
UInt_t yPixels = image.GetHeight();
UInt_t xPixels = image.GetWidth();
UInt_t *argb = image.GetArgbArray();

TH2D *h = new TH2D("h", "Rose histogram", xPixels, -1, 1, yPixels, -1, 1);

for (int row = 0; row < xPixels; ++row) {
   for (int col = 0; col < yPixels; ++col) {
      int index = col * xPixels + row;
      float grey = float(argb[index] & 0xff) / 256;
      h->SetBinContent(row + 1, yPixels - col, grey);
   }
}

gStyle->SetPalette(kCubehelix);
h->Draw("colz");

gROOT->GetListOfCanvases()->Draw()