php生成高清缩略图实例详解

function createsmallimage( $oldimagepath, $newimagepath, $newwidth=154, $newheight=134)
{
  // 取出原图，获得图形信息getimagesize参数说明：0(宽),1(高),2(1gif/2jpg/3png),3(width="638" height="340")
  $oldimageinfo = getimagesize($oldimagepath);
  if ( $oldimageinfo[2] == 1 ) $oldimg = @imagecreatefromgif($oldimagepath);
  elseif ( $oldimageinfo[2] == 2 ) $oldimg = @imagecreatefromjpeg($oldimagepath);
  else $oldimg = @imagecreatefrompng($oldimagepath);
  // 创建图形,imagecreate参数说明：宽,高
  $newimg = imagecreatetruecolor( $newwidth, $newheight );
  //创建色彩,参数：图形,red(0-255),green(0-255),blue(0-255)
  $black = imagecolorallocate( $newimg, 0, 0, 0 ); //黑色
  $white = imagecolorallocate( $newimg, 255, 255, 255 ); //白色
  $red  = imagecolorallocate( $newimg, 255, 0, 0 ); //红色
  $blue = imagecolorallocate( $newimg, 0, 0, 255 ); //蓝色
  $other = imagecolorallocate( $newimg, 0, 255, 0 );
  //新图形高宽处理
  $writenewwidth = $newheight*($oldimageinfo[0] / $oldimageinfo[1]); //要写入的高度
  $writenewheight = $newwidth*($oldimageinfo[1] / $oldimageinfo[0]); //要写入的宽度
  //这样处理图片比例会失调，但可以填满背景
  if ($oldimageinfo[0] / $newwidth > $org_info[1] / $newheight) {
    $writenewwidth = $newwidth;
    $writenewheight = $newwidth / ($oldimageinfo[0] / $oldimageinfo[1]);
  } else {
    $writenewwidth = $newheight * ($oldimageinfo[0] / $oldimageinfo[1]);
    $writenewheight = $newheight;
  }
  //以$newheight为基础,如果新宽小于或等于$newwidth,则成立
  if ( $writenewwidth <= $newwidth ) {
    $writenewwidth = $writenewwidth; //用判断后的大小
    $writenewheight = $newheight; //用规定的大小
    $writex = floor( ($newwidth-$writenewwidth) / 2 ); //在新图片上写入的x位置计算
    $writey = 0;
  } else {
    $writenewwidth = $newwidth; // 用规定的大小
    $writenewheight = $writenewheight; //用判断后的大小
    $writex = 0;
    $writey = floor( ($newheight-$writenewheight) / 2 ); //在新图片上写入的x位置计算
  }
  //旧图形缩小后,写入到新图形上(复制),imagecopyresized参数说明：新旧, 新xy旧xy, 新宽高旧宽高
  @imagecopyresampled( $newimg, $oldimg, $writex, $writey, 0, 0, $writenewwidth, $writenewheight, $oldimageinfo[0], $oldimageinfo[1] );
  //保存文件
//  @imagegif( $newimg, $newimagepath );
  @imagejpeg($newimg, $newimagepath, 100);
  //结束图形
  @imagedestroy($newimg);
}
createsmallimage("./images/jiexie.jpg","./images/jiexie.small.jpg",200,300);
createsmallimage("./images/jiexie.jpg","./images/jiexie.middle.jpg",400,500);