protected static function _sharpenImage($image, $width, $targetWidth)
    {

        // Sharpen image if possible and requested
        if (!!SQUEEZR_IMAGE_SHARPEN && function_exists('imageconvolution')) {
            $intFinal = $targetWidth * (750.0 / $width);
            $intA = 52;
            $intB = -0.27810650887573124;
            $intC = .00047337278106508946;
            $intRes = $intA + $intB * $intFinal + $intC * $intFinal * $intFinal;
            $intSharpness = max(round($intRes), 0);
            $arrMatrix = array(
                array(-1, -2, -1),
                array(-2, $intSharpness + 12, -2),
                array(-1, -2, -1)
            );
            imageconvolution($image, $arrMatrix, $intSharpness, 0);
        }
    }