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();