how pull pristine settlement controlling system.drawing?

i'm perplexing relapse pristine gif an .aspx page arrangement within web page. i am perplexing settlement have transparency, nonetheless i only keep removing black being where settlement should transparent.

does anyone know i'm doing wrong?

protected servant page_load(byval sender object, byval e system.eventargs) _
  handles me.load
    '' change response headers cost gif image.
    response.clear()
    response.contenttype = "image/gif"

    low extent = 110
    low tallness = width

    '' emanate new 32-bit bitmap image
    low b = new bitmap(width, height)

    '' emanate grahpics vigilant drawing
    low g = graphics.fromimage(b)

    low rect = new rectangle(0, 0, extent - 1, tallness - 1)

    '' fill transparent
    low tbrush = new system.drawing.solidbrush(color.transparent)
    g.fillrectangle(tbrush, rect)

    '' pull spin border
    low bpen = pens.red
    g.drawpie(bpen, rect, 0, 365)

    '' fill circle
    low cbrush = new solidbrush(color.lightblue)
    g.fillpie(cbrush, rect, 0, 365)


    '' purify up
    g.flush()
    g.dispose()

    '' transparent
    b.maketransparent()

    b.save(response.outputstream, imaging.imageformat.gif)
    response.flush()
    response.end()
end sub