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HomeBackend DevelopmentPHP Tutorialphp使用gd库函数嵌入水印后,图像变小了

诸位:
     我将一幅JPG图像,通过setWater函数嵌入水印后(图片),像素数没变,但是总大小变小了很多(从1.4M变为350k左右)!!应该是某个函数影响了图像每个像素的丰富度或色彩变化度。。是imagecopy吗?还是imagecreatetruecolor?
请高人指点!!!!下边贴出嵌入水印函数:
//嵌入水印程序, 文字水印和图片水印请分别添加!!!
function setWater($imgSrc,$markImg,$markText,$TextColor,$markPos,$fontType,$markType,$fontSize)
{
/*
参数说明:

$imgSrc:目标图片,可带相对目录地址,
$markImg:水印图片,可带相对目录地址,支持PNG和GIF两种格式,如水印图片在执行文件mark目录下,可写成:mark/mark.gif
$markText:给图片添加的水印文字
$TextColor:水印文字的字体颜色
$markPos:图片水印添加的位置,取值范围:0~9
0:随机位置,在1~8之间随机选取一个位置
1:顶部居左 2:顶部居中 3:顶部居右 4:左边居中
5:图片中心 6:右边居中 7:底部居左 8:底部居中 9:底部居右
$fontType:具体的字体库,可带相对目录地址
$markType:图片添加水印的方式,img代表以图片方式,text代表以文字方式添加水印
*/
    $srcInfo = @getimagesize($imgSrc);
    $srcImg_w    = $srcInfo[0];
    $srcImg_h    = $srcInfo[1];
 
    switch ($srcInfo[2]) 
    { 
        case 1: 
            $srcim =@imagecreatefromgif($imgSrc); 
if($srcim==false)
echo "打开失败!";
            break; 
        case 2: 

            $srcim =@imagecreatefromjpeg($imgSrc); 

if($srcim==false)
echo "打开失败!";
            break; 
        case 3: 
            $srcim =@imagecreatefrompng($imgSrc); 
if($srcim==false)
echo "打开失败!";
            break; 
        default: 
            die("不支持的图片文件类型"); 
            exit; 
    }
    

    if(!strcmp($markType,"img"))
    {
//print_r(" hello ! img");
        if(!file_exists($markImg) || empty($markImg))
        {
            return;
        }
            
        $markImgInfo = @getimagesize($markImg);
        $markImg_w    = $markImgInfo[0];
        $markImg_h    = $markImgInfo[1];
            
        if($srcImg_w          {
            return;
        }
        switch ($markImgInfo[2]) 
        { 
            case 1: 
                $markim =@imagecreatefromgif($markImg); 
if($markim==false)
echo "打开失败!";
                break; 
            case 2: 
                $markim =@imagecreatefromjpeg($markImg); 
if($markim==false)
echo "打开失败!";
                break; 
            case 3: 
                $markim =@imagecreatefrompng($markImg); 
if($markim==false)
echo "打开失败!";
                break; 
            default: 
                die("不支持的水印图片文件类型"); 
                exit; 
        }
            
        $logow = $markImg_w;
        $logoh = $markImg_h;
    }
        
    if(!strcmp($markType,"text"))
    {
        if(!empty($markText))
        {
            if(!file_exists($fontType))
            {
//print_r(" hello ! no fonttype");
                return;
            }
        }
        else 
{
//print_r(" hello ! no marktext");
            return;
        }
            

        $box = imagettfbbox($fontSize, 0, $fontType,$markText);
        $logow = max($box[2], $box[4]) - min($box[0], $box[6]);
        $logoh = max($box[1], $box[3]) - min($box[5], $box[7]);
    }
        
    if($markPos == 0)
    {
        $markPos = rand(1, 9);
    }
        
    switch($markPos)
    {
        case 1:        
            $x = +25;
            $y = +95;
            break;
        case 2:
            $x = ($srcImg_w - $logow) / 2;
            $y = +5;
            break;
        case 3:
            $x = $srcImg_w - $logow - 105;
            $y = +85;
            break;
        case 4:
            $x = +5;
            $y = ($srcImg_h - $logoh) / 2;
            break;
        case 5:
            $x = ($srcImg_w - $logow) / 2;
            $y = ($srcImg_h - $logoh) / 2;
            break;
        case 6:
            $x = $srcImg_w - $logow - 5;
            $y = ($srcImg_h - $logoh) / 2;
            break;
        case 7:
            $x = +5;
            $y = $srcImg_h - $logoh - 5;
            break;
        case 8:
            $x = ($srcImg_w - $logow) / 2;
            $y = $srcImg_h - $logoh - 5;
            break;
        case 9:
            $x = $srcImg_w - $logow - 5;
            $y = $srcImg_h - $logoh -5;
            break;
        default: 
            die("此位置不支持"); 
            exit;
    }

    $dst_img=imagecreatetruecolor($srcImg_w, $srcImg_h); //建立空白背景,真彩色图片

    imagecopy ( $dst_img, $srcim, 0, 0, 0, 0, $srcImg_w, $srcImg_h);

    if(!strcmp($markType,"img"))
    {
        imagecopy($dst_img, $markim, $x, $y, 0, 0, $logow, $logoh);
        imagedestroy($markim);
    }
        
    if(!strcmp($markType,"text"))
    {
//print_r(" hello ! text2");
        $rgb = explode(',', $TextColor);
        $color = imagecolorallocate($dst_img, $rgb[0], $rgb[1], $rgb[2]);
        imagettftext($dst_img, $fontSize, 0, $x, $y, $color, $fontType,$markText);
    }
       
    switch ($srcInfo[2]) 
    { 
        case 1:
            imagegif($dst_img, $imgSrc); 
            break; 
        case 2: 
    //print_r("hello!");
            imagejpeg($dst_img, $imgSrc); 
            break; 
        case 3: 
            imagepng($dst_img, $imgSrc); 
            break;
        default: 
            die("不支持的水印图片文件类型"); 
            exit; 
    }
    imagedestroy($dst_img);
    imagedestroy($srcim);

}


回复讨论(解决方案)

imagejpeg 
第三个参数设置的图片的质量,默认不是最佳。是不是这个原因导致的呢?

是的,多谢指教!网上找的函数,没有逐个函数推敲,只管能用就可以了。多谢多谢!

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