winforms - Drawing transparent pixels in pictureBox C# -

i have picture box, , import .png picture into. when rotate actual image, "free" space of picture box, not include image filled black pixels.

q: how make black pixels transparent?

edit:

here rotation code

public static bitmap rotateimage(image image, pointf offset, float angle)         {             if (image == null)             {                 return null;             }             try             {                 bitmap rotatedbmp = new bitmap(image.width, image.height);                 rotatedbmp.setresolution(image.horizontalresolution, image.verticalresolution);                  using (graphics g = graphics.fromimage(rotatedbmp))                 {                     g.translatetransform(offset.x, offset.y);                     g.rotatetransform(angle);                     g.translatetransform(-offset.x, -offset.y);                     g.drawimage(image, new point(0, 0));                 }                 return rotatedbmp;             }             catch (outofmemoryexception)             {                 gc.collect();             }             catch (argumentexception)             {              }             return image bitmap;         } 

here original , modified images:

picturebox supports transparency if set supportstransparentbackcolor property of system.windows.forms.controlstyles true, put in form_load.

this.setstyle(system.windows.forms.controlstyles.supportstransparentbackcolor, true); 

you can set backcolor on picturebox colour if wish, default defaultbackcolor.