首先dedecms5.3:

打开/includes/image.func.php文件，找到方法function ImageResize()，用下面的代码覆盖（注意备份）。

function ImageResize($srcFile,$toW,$toH,$toFile=”")

{

global $cfg_photo_type;

if($toFile==”")

{

$toFile = $srcFile;

}

$info = “”;

$srcInfo = GetImageSize($srcFile,$info);

switch ($srcInfo[2])

{

case 1:

if(!$cfg_photo_type['gif'])

{

return false;

}

$im = imagecreatefromgif($srcFile);

break;

case 2:

if(!$cfg_photo_type['jpeg'])

{

return false;

}

$im = imagecreatefromjpeg($srcFile);

break;

case 3:

if(!$cfg_photo_type['png'])

{

return false;

}

$im = imagecreatefrompng($srcFile);

break;

case 6:

if(!$cfg_photo_type['bmp'])

{

return false;

}

$im = imagecreatefromwbmp($srcFile);

break;

}

$srcW=ImageSX($im);

$srcH=ImageSY($im);

if($srcW<=$toW && $srcH<=$toH )

{

return true;

}

//缩略生成并裁剪

$newW = $toH * $srcW / $srcH;

$newH = $toW * $srcH / $srcW;

if($newH >= $toH)

{

$ftoW = $toW;

$ftoH = $newH;

}

else

{

$ftoW = $newW;

$ftoH = $toH;

}

if($srcW>$toW||$srcH>$toH)

{

if(function_exists(”imagecreatetruecolor”))

{

@$ni = imagecreatetruecolor($ftoW,$ftoH);

if($ni)

{

imagecopyresampled($ni,$im,0,0,0,0,$ftoW,$ftoH,$srcW,$srcH);

}

else

{

$ni=imagecreate($ftoW,$ftoH);

imagecopyresized($ni,$im,0,0,0,0,$ftoW,$ftoH,$srcW,$srcH);

}

}

else

{

$ni=imagecreate($ftoW,$ftoH);

imagecopyresized($ni,$im,0,0,0,0,$ftoW,$ftoH,$srcW,$srcH);

}

//裁剪图片成标准缩略图

$new_imgx = imagecreatetruecolor($toW,$toH);

if($newH >= $toH)

{

imagecopyresampled($new_imgx,$ni,0,0,0,($newH – $toH)/2,$toW,$toH,$toW,$toH);

}

else

{

imagecopyresampled($new_imgx,$ni,0,0,($newW – $toW)/2,0,$toW,$toH,$toW,$toH);

}

switch ($srcInfo[2])

{

case 1:

imagegif($new_imgx,$toFile);

break;

case 2:

imagejpeg($new_imgx,$toFile,85);

break;

case 3:

imagepng($new_imgx,$toFile);

break;

case 6:

imagebmp($new_imgx,$toFile);

break;

default:

return false;

}

imagedestroy($new_imgx);

imagedestroy($ni);

}

imagedestroy($im);

return true;

}

另外附上dedecms5.5的：

修改文件：image.func.php（或inc_photograph.php）

if($toWH<=$srcWH){

$ftoW=$toW;

$ftoH=$ftoW*($srcH/$srcW);

}

else{

$ftoH=$toH;

$ftoW=$ftoH*($srcW/$srcH);

}

更改为

$ftoH=$toH;

$ftoW=$toW;

if ($toWH<=$srcWH) {

$src_Y = 0;

$src_X = ($srcW-$srcH*$toWH)/2;

$srcW = $srcH*$toWH;

} else {

$src_X = 0;

$src_Y = ($srcH-$srcW/$toWH)/2;

$srcH = $srcW/$toWH;

}

($ni,$im,0,0,0,0,$ftoW,$ftoH,$srcW,$srcH)

更改为

($ni,$im,0,0,$src_X,$src_Y,$ftoW,$ftoH,$srcW,$srcH)

其实就一小小改动，就是在原图中截取最大面积的符合自定义缩略图长宽比列的一部分生成缩略图。