php等比缩放图片

步骤如下:
1.获取图片的基本信息
用这个getimagesize函数

2.判断图片资源类型并创建对应图片资源
用这个getPicType函数(自定义函数)

3.计算缩放比例
原则是取最小的缩放系数.例如:800*600的图片,缩放到200*200以下,则缩放系数为scale=200/800>200/600?200/600:200/800; 因为1/4

4.计算缩放后的尺寸
wdith = floor(800*1/4);向下取整
height = floor(600*1/4);
结果缩放后的图片变为200*150

5.创建目标图像资源
用这个imagecreatetruecolor函数，创建一个真彩的图像

6.等比缩放
用这个imagecopyresampled函数实现缩放

7.输出图像
用这个outputImage函数(自定义函数)

8.释放图片资源
用这个imagedestroy函数

缩放前后如图:
750*525

200*140

代码如下:

Glimmer Ai

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<span>/**
 *<span> @function</span> 等比缩放函数(以保存的方式实现)
 *<span> @param</span> string $picname 被缩放的处理图片源
 *<span> @param</span> int $maxX 缩放后图片的最大宽度
 *<span> @param</span> int $maxY 缩放后图片的最大高度
 *<span> @param</span> string $pre 缩放后图片名的前缀名
 *<span> @return</span> string 返回后的图片名称(带路径),如a.jpg --> s_a.jpg
 */</span><span><span>function</span><span>scalePic</span><span>(<span>$picname</span>,<span>$maxX</span>=<span>100</span>,<span>$maxY</span>=<span>100</span>,<span>$pre</span>=<span>'s_'</span>)</span>
{</span><span>$info</span> = getimagesize(<span>$picname</span>); <span>//获取图片的基本信息</span><span>$width</span> = <span>$info</span>[<span>0</span>];<span>//获取宽度</span><span>$height</span> = <span>$info</span>[<span>1</span>];<span>//获取高度</span><span>//判断图片资源类型并创建对应图片资源</span><span>$im</span> = getPicType(<span>$info</span>[<span>2</span>],<span>$picname</span>);
    <span>//计算缩放比例</span><span>$scale</span> = (<span>$maxX</span>/<span>$width</span>)>(<span>$maxY</span>/<span>$height</span>)?<span>$maxY</span>/<span>$height</span>:<span>$maxX</span>/<span>$width</span>;
    <span>//计算缩放后的尺寸</span><span>$sWidth</span> = floor(<span>$width</span>*<span>$scale</span>);
    <span>$sHeight</span> = floor(<span>$height</span>*<span>$scale</span>);
    <span>//创建目标图像资源</span><span>$nim</span> = imagecreatetruecolor(<span>$sWidth</span>,<span>$sHeight</span>);
    <span>//等比缩放</span>
    imagecopyresampled(<span>$nim</span>,<span>$im</span>,<span>0</span>,<span>0</span>,<span>0</span>,<span>0</span>,<span>$sWidth</span>,<span>$sHeight</span>,<span>$width</span>,<span>$height</span>);
    <span>//输出图像</span><span>$newPicName</span> = outputImage(<span>$picname</span>,<span>$pre</span>,<span>$nim</span>);
    <span>//释放图片资源</span>
    imagedestroy(<span>$im</span>);
    imagedestroy(<span>$nim</span>);
    <span>return</span><span>$newPicName</span>;
}

<span>/**
 * function 判断并返回图片的类型(以资源方式返回)
 *<span> @param</span> int $type 图片类型
 *<span> @param</span> string $picname 图片名字
 *<span> @return</span> 返回对应图片资源
 */</span><span><span>function</span><span>getPicType</span><span>(<span>$type</span>,<span>$picname</span>)</span>
{</span><span>$im</span>=<span>null</span>;
    <span>switch</span>(<span>$type</span>)
    {
        <span>case</span><span>1</span>:  <span>//GIF</span><span>$im</span> = imagecreatefromgif(<span>$picname</span>);
            <span>break</span>;
        <span>case</span><span>2</span>:  <span>//JPG</span><span>$im</span> = imagecreatefromjpeg(<span>$picname</span>);
            <span>break</span>;
        <span>case</span><span>3</span>:  <span>//PNG</span><span>$im</span> = imagecreatefrompng(<span>$picname</span>);
            <span>break</span>;
        <span>case</span><span>4</span>:  <span>//BMP</span><span>$im</span> = imagecreatefromwbmp(<span>$picname</span>);
            <span>break</span>;
        <span>default</span>:
            <span>die</span>(<span>"不认识图片类型"</span>);
            <span>break</span>;
    }
    <span>return</span><span>$im</span>;
}

<span>/**
 * function 输出图像
 *<span> @param</span> string $picname 图片名字
 *<span> @param</span> string $pre 新图片名前缀
 *<span> @param</span> resourse $nim 要输出的图像资源
 *<span> @return</span> 返回新的图片名
 */</span><span><span>function</span><span>outputImage</span><span>(<span>$picname</span>,<span>$pre</span>,<span>$nim</span>)</span>
{</span><span>$info</span> = getimagesize(<span>$picname</span>);
    <span>$picInfo</span> = pathInfo(<span>$picname</span>);
    <span>$newPicName</span> = <span>$picInfo</span>[<span>'dirname'</span>].<span>'/'</span>.<span>$pre</span>.<span>$picInfo</span>[<span>'basename'</span>];<span>//输出文件的路径</span><span>switch</span>(<span>$info</span>[<span>2</span>])
    {
        <span>case</span><span>1</span>:
            imagegif(<span>$nim</span>,<span>$newPicName</span>);
            <span>break</span>;
        <span>case</span><span>2</span>:
            imagejpeg(<span>$nim</span>,<span>$newPicName</span>);
            <span>break</span>;
        <span>case</span><span>3</span>:
            imagepng(<span>$nim</span>,<span>$newPicName</span>);
            <span>break</span>;
        <span>case</span><span>4</span>:
            imagewbmp(<span>$nim</span>,<span>$newPicName</span>);
            <span>break</span>;
    }
    <span>return</span><span>$newPicName</span>;
}

以上就介绍了 php等比缩放图片，包括了方面的内容，希望对PHP教程有兴趣的朋友有所帮助。