How to highlight selected area of an image


There are occasions that customers want to highlight parts of an image. Dynamic Web TWAIN supports that feature with the OverlayRectangle method.


In the following paragraphs, we will introduce how to do this:

  • Select the area
// Use OnImageAreaSelected event to choose the area you want to 
function Dynamsoft_OnImageAreaSelected(index, left, top, right, bottom) { 
  _iLeft = left;
  _iTop = top;
  _iRight = right;
  _iBottom = bottom; } 
// Use OnImageAreaDeselected event to cancel the selection: 
function Dynamsoft_OnImageAreaDeselected(index) { 
  _iLeft = 0;
  _iTop = 0; 
  _iRight = 0; 
  _iBottom = 0; }
  • Highlight the area (here we are adding a gray rectangle)


    _iLeft, _iTop, _iRight, _iBottom, 0x000000/*Int32 ColorRGB*/, 0.5/*Single Opacity*/

Int32 ColorRGB: Specifies the fill color of the rectangle. The byte-ordering of the RGB value is 0xBBGGRR. BB represents blue, GG represents green, RR represents red.
Single Opacity: Specifies the opacity of the rectangle. The value represents opacity. 1.0 is 100% opaque and 0.0 is totally transparent.