/**
	 * 等比例生成縮略圖
	 * @param $imgSrc
	 * @param $resize_width
	 * @param $resize_height
	 * @param $isCut
	 * @author james.ou 2011-11-1
	 */
	public function reSizeImg($imgSrc, $resize_width, $resize_height, $isCut = false) {
		//圖片的類型
		$type = substr(strrchr($imgSrc, "."), 1);
		//初始化圖象
		if ($type == "jpg") {
			$im = imagecreatefromjpeg($imgSrc);
		}
		if ($type == "gif") {
			$im = imagecreatefromgif($imgSrc);
		}
		if ($type == "png") {
			$im = imagecreatefrompng($imgSrc);
		}
		//目標圖象地址
		$full_length = strlen($imgSrc);
		$type_length = strlen($type);
		$name_length = $full_length - $type_length;
		$name = substr($imgSrc, 0, $name_length - 1);
		$dstimg = $name . "_s." . $type;

		$width = imagesx($im);
		$height = imagesy($im);

		//生成圖象
		//改變後的圖象的比例
		$resize_ratio = ($resize_width) / ($resize_height);
		//實際圖象的比例
		$ratio = ($width) / ($height);
		if (($isCut) == 1) { //裁圖
			if ($ratio >= $resize_ratio) { //高度優先
				$newimg = imagecreatetruecolor($resize_width, $resize_height);
				imagecopyresampled($newimg, $im, 0, 0, 0, 0, $resize_width, $resize_height, (($height) * $resize_ratio), $height);
				ImageJpeg($newimg, $dstimg);
			}
			if ($ratio < $resize_ratio) { //寬度優先
				$newimg = imagecreatetruecolor($resize_width, $resize_height);
				imagecopyresampled($newimg, $im, 0, 0, 0, 0, $resize_width, $resize_height, $width, (($width) / $resize_ratio));
				ImageJpeg($newimg, $dstimg);
			}
		} else { //不裁圖
			if ($ratio >= $resize_ratio) {
				$newimg = imagecreatetruecolor($resize_width, ($resize_width) / $ratio);
				imagecopyresampled($newimg, $im, 0, 0, 0, 0, $resize_width, ($resize_width) / $ratio, $width, $height);
				ImageJpeg($newimg, $dstimg);
			}
			if ($ratio < $resize_ratio) {
				$newimg = imagecreatetruecolor(($resize_height) * $ratio, $resize_height);
				imagecopyresampled($newimg, $im, 0, 0, 0, 0, ($resize_height) * $ratio, $resize_height, $width, $height);
				ImageJpeg($newimg, $dstimg);
			}
		}
		ImageDestroy($im);
	}

PHP等比例生成縮略圖