------------------------------------
            gl.bindTexture( gl.TEXTURE_2D, this.texture );
            gl.texImage2D( gl.TEXTURE_2D, 0, gl.RGBA, gl.RGBA, gl.UNSIGNED_BYTE, source );
            //-------------------------------------------------------------------------------

            // compute media size and convert to greyscale
            //-------------------------------------------------------------------------------
            gl.runProgram( this.programGrey, this.texture, this.ping.fbo, xSc