How to generate transparent png image thumbnails in php

Note: This function depends on the GD2 graphics library

I recently wanted to use PHP to generate thumbnails. I searched online and found this article: Generate image thumbnails with PHP

After trying it out, I found the following problems:

1. The thumbnails generated from png images are in jpg format.

2. The thumbnail generated from the png image has no transparent (semi-transparent) effect (filled with black background)

3. The code syntax is relatively old

Therefore, we simply modified and optimized it based on this version.

PHP generate thumbnail class

&lt;?<span>php </span><span>/*</span><span> * desc: Resize Image(png, jpg, gif)
     * author: 十年后的卢哥哥(http://www.cnblogs.com/lurenjiashuo/)
     * date: 2014.11.13
     * base from: http://www.oschina.net/code/snippet_5189_2491 </span><span>*/</span><span>class</span><span> ResizeImage { </span><span>//</span><span>图片类型</span><span>private</span><span>$type</span><span>; </span><span>//</span><span>实际宽度</span><span>private</span><span>$width</span><span>; </span><span>//</span><span>实际高度</span><span>private</span><span>$height</span><span>; </span><span>//</span><span>改变后的宽度</span><span>private</span><span>$resize_width</span><span>; </span><span>//</span><span>改变后的高度</span><span>private</span><span>$resize_height</span><span>; </span><span>//</span><span>是否裁图</span><span>private</span><span>$cut</span><span>; </span><span>//</span><span>源图象</span><span>private</span><span>$srcimg</span><span>; </span><span>//</span><span>目标图象地址</span><span>private</span><span>$dstimg</span><span>; </span><span>//</span><span>临时创建的图象</span><span>private</span><span>$im</span><span>; </span><span>function</span> __construct(<span>$imgPath</span>, <span>$width</span>, <span>$height</span>, <span>$isCut</span>, <span>$savePath</span><span>) { </span><span>$this</span>-&gt;srcimg = <span>$imgPath</span><span>; </span><span>$this</span>-&gt;resize_width = <span>$width</span><span>; </span><span>$this</span>-&gt;resize_height = <span>$height</span><span>; </span><span>$this</span>-&gt;cut = <span>$isCut</span><span>; </span><span>//</span><span>图片的类型</span><span>$this</span>-&gt;type = <span>strtolower</span>(<span>substr</span>(<span>strrchr</span>(<span>$this</span>-&gt;srcimg,"."),1<span>)); </span><span>//</span><span>初始化图象</span><span>$this</span>-&gt;<span>initi_img(); </span><span>//</span><span>目标图象地址</span><span>$this</span> -&gt; dst_img(<span>$savePath</span><span>); </span><span>//</span><span>--</span><span>$this</span>-&gt;width = imagesx(<span>$this</span>-&gt;<span>im); </span><span>$this</span>-&gt;height = imagesy(<span>$this</span>-&gt;<span>im); </span><span>//</span><span>生成图象</span><span>$this</span>-&gt;<span>newimg();
            ImageDestroy (</span><span>$this</span>-&gt;<span>im);
        } </span><span>private</span><span>function</span><span> newimg() { </span><span>//</span><span>改变后的图象的比例</span><span>$resize_ratio</span> = (<span>$this</span>-&gt;resize_width)/(<span>$this</span>-&gt;<span>resize_height); </span><span>//</span><span>实际图象的比例</span><span>$ratio</span> = (<span>$this</span>-&gt;width)/(<span>$this</span>-&gt;<span>height); </span><span>if</span>(<span>$this</span>-&gt;<span>cut) { </span><span>//</span><span>裁图</span><span>$newimg</span> = imagecreatetruecolor(<span>$this</span>-&gt;resize_width,<span>$this</span>-&gt;<span>resize_height); </span><span>if</span>(<span>$this</span>-&gt;type=="png"<span>) {
                    imagefill(</span><span>$newimg</span>, 0, 0, imagecolorallocatealpha(<span>$newimg</span>, 0, 0, 0, 127<span>));
                } </span><span>if</span>(<span>$ratio</span>&gt;=<span>$resize_ratio</span><span>) { </span><span>//</span><span>高度优先</span> imagecopyresampled(<span>$newimg</span>, <span>$this</span>-&gt;im, 0, 0, 0, 0, <span>$this</span>-&gt;resize_width,<span>$this</span>-&gt;resize_height, ((<span>$this</span>-&gt;height)*<span>$resize_ratio</span>), <span>$this</span>-&gt;<span>height);
                } </span><span>else</span><span> { </span><span>//</span><span>宽度优先</span> imagecopyresampled(<span>$newimg</span>, <span>$this</span>-&gt;im, 0, 0, 0, 0, <span>$this</span>-&gt;resize_width, <span>$this</span>-&gt;resize_height, <span>$this</span>-&gt;width, ((<span>$this</span>-&gt;width)/<span>$resize_ratio</span><span>));
                }
            } </span><span>else</span><span> { </span><span>//</span><span>不裁图</span><span>if</span>(<span>$ratio</span>&gt;=<span>$resize_ratio</span><span>) { </span><span>$newimg</span> = imagecreatetruecolor(<span>$this</span>-&gt;resize_width,(<span>$this</span>-&gt;resize_width)/<span>$ratio</span><span>); </span><span>if</span>(<span>$this</span>-&gt;type=="png"<span>) {
                        imagefill(</span><span>$newimg</span>, 0, 0, imagecolorallocatealpha(<span>$newimg</span>, 0, 0, 0, 127<span>));
                    }
                    imagecopyresampled(</span><span>$newimg</span>, <span>$this</span>-&gt;im, 0, 0, 0, 0, <span>$this</span>-&gt;resize_width, (<span>$this</span>-&gt;resize_width)/<span>$ratio</span>, <span>$this</span>-&gt;width, <span>$this</span>-&gt;<span>height);
                } </span><span>else</span><span> { </span><span>$newimg</span> = imagecreatetruecolor((<span>$this</span>-&gt;resize_height)*<span>$ratio</span>,<span>$this</span>-&gt;<span>resize_height); </span><span>if</span>(<span>$this</span>-&gt;type=="png"<span>) {
                        imagefill(</span><span>$newimg</span>, 0, 0, imagecolorallocatealpha(<span>$newimg</span>, 0, 0, 0, 127<span>));
                    }
                    imagecopyresampled(</span><span>$newimg</span>, <span>$this</span>-&gt;im, 0, 0, 0, 0, (<span>$this</span>-&gt;resize_height)*<span>$ratio</span>, <span>$this</span>-&gt;resize_height, <span>$this</span>-&gt;width, <span>$this</span>-&gt;<span>height);
                }
            } </span><span>if</span>(<span>$this</span>-&gt;type=="png"<span>) {
                imagesavealpha(</span><span>$newimg</span>, <span>true</span><span>);
                imagepng (</span><span>$newimg</span>,<span>$this</span>-&gt;<span>dstimg);
            } </span><span>else</span><span> {
                imagejpeg (</span><span>$newimg</span>,<span>$this</span>-&gt;<span>dstimg);
            }
        } </span><span>//</span><span>初始化图象</span><span>private</span><span>function</span><span> initi_img() { </span><span>if</span>(<span>$this</span>-&gt;type=="jpg"<span>) { </span><span>$this</span>-&gt;im = imagecreatefromjpeg(<span>$this</span>-&gt;<span>srcimg);
            } </span><span>if</span>(<span>$this</span>-&gt;type=="gif"<span>) { </span><span>$this</span>-&gt;im = imagecreatefromgif(<span>$this</span>-&gt;<span>srcimg);
            } </span><span>if</span>(<span>$this</span>-&gt;type=="png"<span>) { </span><span>$this</span>-&gt;im = imagecreatefrompng(<span>$this</span>-&gt;<span>srcimg);
            }
        } </span><span>//</span><span>图象目标地址</span><span>private</span><span>function</span> dst_img(<span>$dstpath</span><span>) { </span><span>$full_length</span> = <span>strlen</span>(<span>$this</span>-&gt;<span>srcimg); </span><span>$type_length</span> = <span>strlen</span>(<span>$this</span>-&gt;<span>type); </span><span>$name_length</span> = <span>$full_length</span>-<span>$type_length</span><span>; </span><span>$name</span> = <span>substr</span>(<span>$this</span>-&gt;srcimg,0,<span>$name_length</span>-1<span>); </span><span>$this</span>-&gt;dstimg = <span>$dstpath</span><span>;
        }
    } </span>?&gt;

use

When using it, just call the constructor of the class directly. The constructor is as follows:

<span>$resizeimage</span> = <span>new</span> resizeimage($imgPath, $width, $height, $isCut, $savePath);

parameters

$imgPath: original image address

$width: thumbnail width

$height: Thumbnail height

$isCut: Whether to crop, bool value

$savePath: thumbnail address (can be the same as the original image address)

Example

&lt;?<span>php </span><span>include</span> "ResizeImage.php"<span>; </span><span>//</span><span>jpg</span><span>$jpgResize</span> = <span>new</span> ResizeImage("img/test_1920_1200.jpg", 320, 240, <span>false</span>, "img/test_320_240.jpg"<span>); </span><span>//</span><span>png</span><span>$pngResize</span> = <span>new</span> ResizeImage("img/test_1024_746.png", 320, 240, <span>false</span>, "img/test_320_240.png"<span>); </span>?&gt;

Effect

The above introduces how PHP generates transparent png image thumbnails, including the content of generating thumbnails in PHP. I hope it will be helpful to friends who are interested in PHP tutorials.