Claire's Blog

常常在處理一些使用者上傳的圖片時
會需要讓系統自動產生圖檔的縮圖(例如無名的相簿預覽等等的功能)PHP程式在處理圖片縮圖的方式
較常見的有兩種: GD ，以及ImageMagick
GD是php內建的圖形函式庫，一般只要安裝php都會有內建此功能
而ImageMagick則是要另外安裝，再用下面的方法呼叫:
// 呼叫 ImageMagic 的 convert exec(“convert -geometry 200×200 big_img.jpg small_img.jpg“);

其它的參數
1.生成縮圖
a.指定大小 # convert -sample 80×40 input.jpg output.jpg
b.利用比例 # convert -sample 25%x25% input.jpg output.jpg

2.旋轉圖形
利用cotate參數，+90表順時針旋轉90度，而-90則表逆時針轉90度
# convert -rotate 90 input.jpg output.jpg

3.轉換格式
以附檔名為準，如下例就是將jpg轉換成png的用法
# convert input.jpg output.png

4.一次使用多種命令
# convert -sample 25%x25% -spread 4 \ -charcoal 4 input.jpg output.jpg

詳細使用方法請參照:
http://www.imagemagick.org/script/index.php

GD圖形函式庫除的詳細功能可參照:
http://www.php5.idv.tw/modules.php?mod=books&act=index&cid=29
下面為一個用GD函式庫所寫成的縮圖函式。

class resize_img
{
  var $image_path = '';
  //holds the image path
  var $sizelimit_x = 250;
  //the limit of the image width
  var $sizelimit_y = 250;
  //the limit of the image height
  var $image_resource = '';
  //holds the image resource
  var $keep_proportions = true;
  //if true it keeps the image proportions when resized
  var $resized_resource = '';
  //holds the resized image resource
  var $hasGD = false;
  var $output = 'SAME';
  //can be JPG, GIF, PNG, or SAME (same will save as old type)

  function resize_img()
  {
    if( function_exists('gd_info') ){ $this->hasGD = true; }
  }

  function resize_image( $image_path )
  {
    if( $this->hasGD === false ){ return false; }
    //no GD installed on the server!

    list($img_width, $img_height, $img_type, $img_attr) =

           @getimagesize( $image_path );
    //this is going to get the image width, height, and format

    if( ( $img_width != 0 ) || ( $img_width != 0 ) )
    //make sure it was loaded correctly
    {
      switch( $img_type )
      {
        case 1:
          //GIF
          $this->image_resource = @imagecreatefromgif( $image_path );
          if( $this->output == 'SAME' ){ $this->output = 'GIF'; }
          break;
        case 2:
          //JPG
          $this->image_resource = @imagecreatefromjpeg( $image_path );
          if( $this->output == 'SAME' ){ $this->output = 'JPG'; }
          break;
        case 3:
          //PNG
          $this->image_resource = @imagecreatefrompng( $image_path );
          if( $this->output == 'SAME' ){ $this->output = 'PNG'; }
      }
      if( $this->image_resource === '' ){ return false; }
      //it wasn't able to load the image
    }
    else{ return false; }
    //something happened!

    if( $this->keep_proportions === true )
    {
      if( ($img_width-$this->sizelimit_x) > ($img_height-$this->sizelimit_y) )
      {
      //if the width of the img is greater than the size limit we scale by width
        $scalex = ( $this->sizelimit_x / $img_width );
        $scaley = $scalex;
      }
      else
      //if the height of the img is greater than the size limit we scale by height
      {
        $scalex = ( $this->sizelimit_y / $img_height );
        $scaley = $scalex;
      }

    }
    else
    {
      $scalex = ( $this->sizelimit_x / $img_width );
      $scaley = ( $this->sizelimit_y / $img_height );
      //just make the image fit the image size limit

      if( $scalex > 1 ){ $scalex = 1; }
      if( $scaley > 1 ){ $scaley = 1; }
      //don't make it so it streches the image
    }

    $new_width = $img_width * $scalex;
    $new_height = $img_height * $scaley;

    $this->resized_resource =

           @imagecreatetruecolor( $new_width, $new_height );
    //creates an image resource,

    //with the width and height of the size limits (or new resized proportion )

    if( function_exists( 'imageantialias' )){

            @imageantialias( $this->resized_resource, true );

    }
    //helps in the quality of the image being resized

    @imagecopyresampled( $this->resized_resource, $this->image_resource, 0, 0, 0, 0,

          $new_width, $new_height, $img_width, $img_height );
    //resize the iamge onto the resized resource

    @imagedestroy( $this->image_resource );
    //destory old image resource

    return true;
  }

  function save_resizedimage( $path, $name )
  {
    switch( strtoupper($this->output) )
    {
      case 'GIF':
        //GIF
        @imagegif( $this->resized_resource, $path . $name . '.gif' );
        break;
      case 'JPG':
        //JPG
        @imagejpeg( $this->resized_resource, $path . $name . '.jpg' );
        break;
      case 'PNG':
        //PNG
        @imagepng( $this->resized_resource, $path . $name . '.png' );
    }
  }

  function output_resizedimage()
  {
    $the_time = time();
    header('Last-Modified: ' . date( 'D, d M Y H:i:s', $the_time ) . ' GMT');
    header('Cache-Control: public');

    switch( strtoupper($this->output) )
    {
      case 'GIF':
        //GIF
        header('Content-type: image/gif');
        @imagegif( $this->resized_resource );
        break;
      case 'JPG':
        //JPG
        header('Content-type: image/jpg');
        @imagejpeg( $this->resized_resource );
        break;
      case 'PNG':
        //PNG
        header('Content-type: image/png');
        @imagepng( $this->resized_resource );
    }
  }

  function destroy_resizedimage()
  {
    @imagedestroy( $this->resized_resource );
    @imagedestroy( $this->image_resource );
  }

}

//how to use the class:
//makes a simple thumbnail of an image of 100x100

//and saves the image then outputs it.
$imgresize = new resize_img();

$imgresize->sizelimit_x = 100;
$imgresize->sizelimit_y = 100;
$imgresize->keep_proportions = true;
$imgresize->output = 'PNG';

if( $imgresize->resize_image('C:/treeshadows_001.gif' ) === false )
{
  echo 'ERROR!';
}
else
{
  $imgresize->save_resizedimage( 'C:/xampp/', 'treeshadows_001' );
  $imgresize->output_resizedimage();
}

$imgresize->destroy_resizedimage();