php图片压缩可以通过GD库来实现。以下是一个使用GD库进行图片压缩的示例代码：

// 原始图片路径
$sourceImage = 'path/to/source/image.jpg'; 
// 压缩后保存的路径及文件名
$compressedImage = 'path/to/compressed/image.jpg'; 
// 压缩后的图片质量（1-100，100为最高质量）
$compressionQuality = 80; 
// 获取原始图片的信息
$imageInfo = getimagesize($sourceImage);
$originalWidth = $imageInfo[0];
$originalHeight = $imageInfo[1]; 
// 创建一个空白画布
$compressed = imagecreatetruecolor($originalWidth, $originalHeight); 
// 根据原始图片的格式创建一个新的图片资源
if ($imageInfo['mime'] == 'image/jpeg' || $imageInfo['mime'] == 'image/pjpeg') {$source = imagecreatefromjpeg($sourceImage);
} elseif ($imageInfo['mime'] == 'image/png' || $imageInfo['mime'] == 'image/x-png') {$source = imagecreatefrompng($sourceImage);
}// 将原始图片复制到新的画布上并进行压缩
imagecopyresampled($compressed, $source, 0, 0, 0, 0, $originalWidth, $originalHeight, $originalWidth, $originalHeight);// 保存压缩后的图片
imagejpeg($compressed, $compressedImage, $compressionQuality); 
// 释放内存
imagedestroy($compressed);
imagedestroy($source); 
echo '图片压缩完成！';

PHP实现图片压缩同时保持清晰度

<?php/*** 图片压缩类：通过缩放来压缩。* 如果要保持源图比例，把参数$percent保持为1即可。* 即使原比例压缩，也可大幅度缩小。数码相机4M图片。也可以缩为700KB左右。如果缩小比例，则体积会更小。** 结果：可保存、可直接显示。*/
class imgcompress{private $src;private $image;private $imageinfo;private $percent = 0.5;/*** 图片压缩* @param $src 源图* @param float $percent  压缩比例*/public function __construct($src, $percent=1){$this->src = $src;$this->percent = $percent;}/** 高清压缩图片* @param string $saveName  提供图片名（可不带扩展名，用源图扩展名）用于保存。或不提供文件名直接显示*/public function compressImg($saveName=''){$this->_openImage();if(!empty($saveName)) $this->_saveImage($saveName);  //保存else $this->_showImage();}/*** 内部：打开图片*/private function _openImage(){list($width, $height, $type, $attr) = getimagesize($this->src);$this->imageinfo = array('width'=>$width,'height'=>$height,'type'=>image_type_to_extension($type,false),'attr'=>$attr);$fun = "imagecreatefrom".$this->imageinfo['type'];$this->image = $fun($this->src);$this->_thumpImage();}/*** 内部：操作图片*/private function _thumpImage(){$new_width = $this->imageinfo['width'] * $this->percent;$new_height = $this->imageinfo['height'] * $this->percent;$image_thump = imagecreatetruecolor($new_width,$new_height);//将原图复制带图片载体上面，并且按照一定比例压缩,极大的保持了清晰度imagecopyresampled($image_thump,$this->image,0,0,0,0,$new_width,$new_height,$this->imageinfo['width'],$this->imageinfo['height']);imagedestroy($this->image);$this->image = $image_thump;}/*** 输出图片:保存图片则用saveImage()*/private function _showImage(){header('Content-Type: image/'.$this->imageinfo['type']);$funcs = "image".$this->imageinfo['type'];$funcs($this->image);}/*** 保存图片到硬盘：* @param  string $dstImgName  1、可指定字符串不带后缀的名称，使用源图扩展名 。2、直接指定目标图片名带扩展名。*/private function _saveImage($dstImgName){if(empty($dstImgName)) return false;$allowImgs = ['.jpg', '.jpeg', '.png', '.bmp', '.wbmp','.gif'];   //如果目标图片名有后缀就用目标图片扩展名 后缀，如果没有，则用源图的扩展名$dstExt =  strrchr($dstImgName ,".");$sourseExt = strrchr($this->src ,".");if(!empty($dstExt)) $dstExt =strtolower($dstExt);if(!empty($sourseExt)) $sourseExt =strtolower($sourseExt);//有指定目标名扩展名if(!empty($dstExt) && in_array($dstExt,$allowImgs)){$dstName = $dstImgName;}elseif(!empty($sourseExt) && in_array($sourseExt,$allowImgs)){$dstName = $dstImgName.$sourseExt;}else{$dstName = $dstImgName.$this->imageinfo['type'];}$funcs = "image".$this->imageinfo['type'];$funcs($this->image,$dstName);}/*** 销毁图片*/public function __destruct(){imagedestroy($this->image);}
}
$source =  '123.png';//原图片名称
$dst_img = 'text.png';//压缩后图片的名称
$percent = 1;  #原图压缩，不缩放，但体积大大降低
$image = (new imgcompress($source,$percent))->compressImg($dst_img);

批量压缩

/*** 扫描文件夹* @param $path_dir*/
function scan_dir($path_dir){if (!is_dir($path_dir)) return false;$rs = scandir($path_dir);foreach ($rs as $k => $v){if ($v === '.' || $v === '..') continue;$path = $path_dir.rtrim($v,'/');if (is_file($path)){$image = (new imgcompress($path, 1))->compressImg($path);log_msg("{$path}---");continue;}if (is_dir($path."/")) scan_dir($path."/");}
}
function log_msg($msg){echo "$msg\r\n";
}
/*开始扫描文件夹*/
$source_dir = "./testimages/";//目标路径
scan_dir($source_dir);