PHP can also resize JPEG images!

In the previous article "Why is the === operator in PHP faster than ==? 》Introduced to you why the === operator in PHP is faster than ==. Friends who are interested can learn about it~

The theme of this article is to teach you how to adjust JPEG in PHP Image size.

In the process of website development, we sometimes encounter requirements to implement the function of scaling images, such as cover images, thumbnails, information pictures, etc. The size of the image must be specified according to the needs, but everyone should also know that we can use HTML to modify the image size, as follows:

<img src="/static/imghwm/default1.png"  data-src="001.jpg"  class="lazy"      style="max-width:90%"  style="max-width:90%" alt="图片尺寸">

Of course, the focus of this article is to use PHP to adjust the image size. Let’s take a look directly. Code:

The PHP code is as follows:

<?php

$filename = &#39;001.jpg&#39;;

// 最大宽度和高度
$width = 100;
$height = 100;

// 文件类型
header(&#39;Content-Type: image/jpg&#39;);

// 新尺寸
list($width_orig, $height_orig) = getimagesize($filename);

$ratio_orig = $width_orig/$height_orig;

if ($width/$height > $ratio_orig) {
    $width = $height*$ratio_orig;
} else {
    $height = $width/$ratio_orig;
}

// 重采样的图像
$image_p = imagecreatetruecolor($width, $height);
$image = imagecreatefromjpeg($filename);

imagecopyresampled($image_p, $image, 0, 0, 0, 0,
    $width, $height, $width_orig, $height_orig);

// 输出图像
imagejpeg($image_p, null, 100);

The effect is as follows:

Here you need to master an important Function imagecopyresampled():

(This function is applicable to versions PHP 4 >= 4.0.6, PHP 5, PHP 7, PHP 8)

imagecopyresampled — Resample and copy part of the image and resize it;

Syntax:

imagecopyresampled(
    resource $dst_image,
    resource $src_image,
    int $dst_x,
    int $dst_y,
    int $src_x,
    int $src_y,
    int $dst_w,
    int $dst_h,
    int $src_w,
    int $src_h
): bool

Parameters respectively represent:

dst_image：目标图象资源。
src_image：源图象资源。
dst_x：目标 X 坐标点。
dst_y：目标 Y 坐标点。
src_x：源的 X 坐标点。
src_y：源的 Y 坐标点。
dst_w：目标宽度。
dst_h：目标高度。
src_w：源图象的宽度。
src_h：源图象的高度。

imagecopyresampled() Copy a square in an image Regions are copied into another image, interpolating pixel values ​​smoothly and thus, inter alia, reducing the size of the image while still maintaining great sharpness.

In other words, imagecopyresampled() will take a rectangular area from src_image of width src_w and height src_h at position (src_x,src_y) and place it in a rectangular area of dst_image of width dst_w and height dst_h at position (dst_x,dst_y).

If the source and target have different widths and heights, corresponding image shrinking and stretching will occur. The coordinates refer to the upper left corner. This function can be used to copy regions within the same image (if dst_image and src_image are the same), but the results are unpredictable if the regions overlap.

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