php等比縮放圖片

步驟如下:
1.取得圖片的基本資訊
用這個getimagesize函數

2.判斷圖片資源類型並建立對應圖片資源
用這個getPicType函數(自訂函數)

3.計算縮放比例
原則是取最小的縮放係數.例如:800*600的圖片,縮放到200*200以下,則縮放係數為scale=200/800>200/600?200/600:200/800; 因為1/4

4.計算縮放後的尺寸
wdith = floor(800*1/4);向下取整
height = floor(600*1/4);
結果縮放後的圖片變成200*150

5.建立目標影像資源
用這個imagecreatetruecolor函數，創建一個真彩的圖像

6.等比縮放
用這個imagecopyresampled函數實現縮放

7.輸出圖像
用這個outputImage函數(自訂函數)

8.釋放圖片資源
用這個imagedestroy函數

縮放前後如圖:
750*525

200*140

程式碼如下:

<code><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>;
}</code>

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以上就介紹了 php等比縮放圖片，包括了方面的內容，希望對PHP教程有興趣的朋友有幫助。