PHP 图片缩略图的实现方法

功能：支持jpg,jpeg,gif,png,bmp图片格式，支持按原图片的比例进行缩放，可以选择在图片缩放的过程中是否需要对图片进行裁切，加入了图片质量控制，可以实现缩略图片质量最高化。

完整类的代码如下：

<?php
/**
 * 功能：php生成缩略图片的类
 */
 class ResizeImage{
  public $type;//图片类型
  public $width;//实际宽度
  public $height;//实际高度
  public $resize_width;//改变后的宽度
  public $resize_height;//改变后的高度
  public $cut;//是否裁图
  public $srcimg;//源图象
  public $dstimg;//目标图象地址
  public $im;//临时创建的图象
  public $quality;//图片质量
  function resizeimage($img,$wid,$hei,$c,$dstpath,$quality=100){
  $this->srcimg=$img;
  $this->resize_width=$wid;
  $this->resize_height=$hei;
  $this->cut=$c;
  $this->quality=$quality;
  $this->type=strtolower(substr(strrchr($this->srcimg,'.'),1));//图片的类型
  $this->initi_img();//初始化图象
  $this -> dst_img($dstpath);//目标图象地址
  @$this->width=imagesx($this->im);
  @$this->height=imagesy($this->im);
  $this->newimg();//生成图象
  @ImageDestroy($this->im);
  }
  function newimg(){
  $resize_ratio=($this->resize_width)/($this->resize_height);//改变后的图象的比例
  @$ratio=($this->width)/($this->height);//实际图象的比例
  if(($this->cut)=='1'){//裁图
    if($img_func==='imagepng'&&(str_replace('.','',PHP_VERSION)>=512)){ //针对php版本大于5.12参数变化后的处理情况
    $quality=9;
    }
    if($ratio>=$resize_ratio){//高度优先
    $newimg=imagecreatetruecolor($this->resize_width,$this->resize_height);
    imagecopyresampled($newimg,$this->im,0,0,0,0,$this->resize_width,$this->resize_height,(($this->height)*$resize_ratio),$this->height);
    imagejpeg($newimg,$this->dstimg,$this->quality);
    }
    if($ratio<$resize_ratio){//宽度优先
    $newimg=imagecreatetruecolor($this->resize_width,$this->resize_height);
    imagecopyresampled($newimg,$this->im,0,0,0,0,$this->resize_width,$this->resize_height,$this->width,(($this->width)/$resize_ratio));
    imagejpeg($newimg,$this->dstimg,$this->quality);
    }
  }else{//不裁图
    if($ratio>=$resize_ratio){
    $newimg=imagecreatetruecolor($this->resize_width,($this->resize_width)/$ratio);
    imagecopyresampled($newimg,$this->im,0,0,0,0,$this->resize_width,($this->resize_width)/$ratio,$this->width,$this->height);
    imagejpeg($newimg,$this->dstimg,$this->quality);
    }
    if($ratio<$resize_ratio){
    @$newimg=imagecreatetruecolor(($this->resize_height)*$ratio,$this->resize_height);
    @imagecopyresampled($newimg,$this->im,0,0,0,0,($this->resize_height)*$ratio,$this->resize_height,$this->width,$this->height);
    @imagejpeg($newimg,$this->dstimg,$this->quality);
    }
  }
  }
  function initi_img(){//初始化图象
  if($this->type=='jpg' || $this->type=='jpeg'){
    $this->im=imagecreatefromjpeg($this->srcimg);
  }
  if($this->type=='gif'){
    $this->im=imagecreatefromgif($this->srcimg);
  }
  if($this->type=='png'){
    $this->im=imagecreatefrompng($this->srcimg);
  }
  if($this->type=='wbm'){
    @$this->im=imagecreatefromwbmp($this->srcimg);
  }
  if($this->type=='bmp'){
    $this->im=$this->ImageCreateFromBMP($this->srcimg);
  }
  }
  function dst_img($dstpath){//图象目标地址
  $full_length=strlen($this->srcimg);
  $type_length=strlen($this->type);
  $name_length=$full_length-$type_length;
  $name=substr($this->srcimg,0,$name_length-1);
  $this->dstimg=$dstpath;
  //echo $this->dstimg;
  }
   
  function ImageCreateFromBMP($filename){ //自定义函数处理bmp图片
  if(!$f1=fopen($filename,"rb"))returnFALSE;
  $FILE=unpack("vfile_type/Vfile_size/Vreserved/Vbitmap_offset",fread($f1,14));
  if($FILE['file_type']!=19778)returnFALSE;
  $BMP=unpack('Vheader_size/Vwidth/Vheight/vplanes/vbits_per_pixel'.
    '/Vcompression/Vsize_bitmap/Vhoriz_resolution'.
    '/Vvert_resolution/Vcolors_used/Vcolors_important',fread($f1,40));
  $BMP['colors']=pow(2,$BMP['bits_per_pixel']);
  if($BMP['size_bitmap']==0)$BMP['size_bitmap']=$FILE['file_size']-$FILE['bitmap_offset'];
  $BMP['bytes_per_pixel']=$BMP['bits_per_pixel']/8;
  $BMP['bytes_per_pixel2']=ceil($BMP['bytes_per_pixel']);
  $BMP['decal']=($BMP['width']*$BMP['bytes_per_pixel']/4);
  $BMP['decal']-=floor($BMP['width']*$BMP['bytes_per_pixel']/4);
  $BMP['decal']=4-(4*$BMP['decal']);
  if($BMP['decal']==4)$BMP['decal']=0;
  $PALETTE=array();
  if($BMP['colors']<16777216)
  {
    $PALETTE=unpack('V'.$BMP['colors'],fread($f1,$BMP['colors']*4));
  }
  $IMG=fread($f1,$BMP['size_bitmap']);
  $VIDE=chr(0);
  $res=imagecreatetruecolor($BMP['width'],$BMP['height']);
  $P=0;
  $Y=$BMP['height']-1;
  while($Y>=0)
  {
    $X=0;
    while($X<$BMP['width'])
    {
    if($BMP['bits_per_pixel']==24)
      $COLOR=unpack("V",substr($IMG,$P,3).$VIDE);
    elseif($BMP['bits_per_pixel']==16)
    {
      $COLOR=unpack("n",substr($IMG,$P,2));
      $COLOR[1]=$PALETTE[$COLOR[1]+1];
    }
    elseif($BMP['bits_per_pixel']==8)
    {
      $COLOR=unpack("n",$VIDE.substr($IMG,$P,1));
      $COLOR[1]=$PALETTE[$COLOR[1]+1];
    }
    elseif($BMP['bits_per_pixel']==4)
    {
      $COLOR=unpack("n",$VIDE.substr($IMG,floor($P),1));
      if(($P*2)%2==0)$COLOR[1]=($COLOR[1]>>4);else$COLOR[1]=($COLOR[1]&0x0F);
      $COLOR[1]=$PALETTE[$COLOR[1]+1];
    }
    elseif($BMP['bits_per_pixel']==1)
    {
      $COLOR=unpack("n",$VIDE.substr($IMG,floor($P),1));
      if(($P*8)%8==0)$COLOR[1]=$COLOR[1]>>7;
      elseif(($P*8)%8==1)$COLOR[1]=($COLOR[1]&0x40)>>6;
      elseif(($P*8)%8==2)$COLOR[1]=($COLOR[1]&0x20)>>5;
      elseif(($P*8)%8==3)$COLOR[1]=($COLOR[1]&0x10)>>4;
      elseif(($P*8)%8==4)$COLOR[1]=($COLOR[1]&0x8)>>3;
      elseif(($P*8)%8==5)$COLOR[1]=($COLOR[1]&0x4)>>2;
      elseif(($P*8)%8==6)$COLOR[1]=($COLOR[1]&0x2)>>1;
      elseif(($P*8)%8==7)$COLOR[1]=($COLOR[1]&0x1);
      $COLOR[1]=$PALETTE[$COLOR[1]+1];
    }
    else
      returnFALSE;
    imagesetpixel($res,$X,$Y,$COLOR[1]);
    $X++;
    $P+=$BMP['bytes_per_pixel'];
    }
    $Y--;
    $P+=$BMP['decal'];
  }
  fclose($f1);
  return$res;
  }
   
 }
?>

使用方法很简单代码如下：