e it
            // gl.bindBuffer( gl.PIXEL_PACK_BUFFER, null );
            //-------------------------------------------------------------------------------

            // read processed image pixels from ping pong buffer
            //-------------------------------------------------------------------------------
            gl.bindFramebuffer( gl.FRAMEBUFFER, this.ping.fbo );
            gl.readPixels( 0, 0, gl.canvas.width, gl.canvas.height, gl.RGBA, gl.FLOAT, this.rgba );
            gl.bindFramebuff