Changing the size of an image is a very common functional requirement. Let’s start studying how to change the size of an image in PHP. Let me first introduce a function I wrote myself.
<?php $imgsrc = "http://www.bkjia.com/images/3.jpg"; $width = 780; $height = 420; resizejpg($imgsrc,$imgdst,$width,$height); function resizejpg($imgsrc,$imgdst,$imgwidth,$imgheight) { //$imgsrc jpg格式图像路径 $imgdst jpg格式图像保存文件名 $imgwidth要改变的宽度 $imgheight要改变的高度 //取得图片的宽度,高度值 $arr = getimagesize($imgsrc); header("Content-type: image/jpg"); $imgWidth = $imgwidth; $imgHeight = $imgheight; // Create image and define colors $imgsrc = imagecreatefromjpeg($imgsrc); $image = imagecreatetruecolor($imgWidth, $imgHeight); //创建一个彩色的底图 imagecopyresampled($image, $imgsrc, 0, 0, 0, 0,$imgWidth,$imgHeight,$arr[0], $arr[1]); imagepng($image); imagedestroy($image); } ?>
imagecopyresampled
imagecopyresampled -- resample and resize part of the image.
int imagecopyresampled ( resource dst_im, resource src_im, int dstX, int dstY, int srcX, int srcY, int dstW, int dstH, int srcW, int srcH)
imagecopyresampled() copies a square area from one image to another, smoothly interpolating pixel values and thus, inter alia, reducing the size of the image while still maintaining great sharpness. dst_im and src_im are the identifiers of the target image and source image respectively. If the source and destination have different widths and heights, the image shrinks and stretches accordingly. The coordinates refer to the upper left corner. This function can be used to copy regions within the same image (if dst_im and src_im are the same), but the results are unpredictable if the regions overlap.
Note: There is a problem because of the palette image limit (255+1 colors). Resampling or filtering an image often requires more than 255 colors, and an approximation is used in calculating the new resampled pixels and their colors. When trying to assign a new color to a palette image, if that fails we choose the closest (theoretically) calculated color. This is not always the visually closest color. This can produce weird results, such as blank (or visually blank) images. To bypass this problem, use a truecolor image as the target image, such as one created with imagecreatetruecolor().
Note: imagecopyresampled() requires GD 2.0.l or higher.
A simple example:
<?php // The file $filename = 'test.jpg'; $percent = 0.5; // Content type header('Content-Type: image/jpeg'); // Get new dimensions list($width, $height) = getimagesize($filename); $new_width = $width * $percent; $new_height = $height * $percent; // Resample $image_p = imagecreatetruecolor($new_width, $new_height); $image = imagecreatefromjpeg($filename); imagecopyresampled($image_p, $image, 0, 0, 0, 0, $new_width, $new_height, $width, $height); // Output imagejpeg($image_p, null, 100); ?>
Example 2:
<?php // The file $filename = 'test.jpg'; // Set a maximum height and width $width = 200; $height = 200; // Content type header('Content-Type: image/jpeg'); // Get new dimensions list($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; } // Resample $image_p = imagecreatetruecolor($width, $height); $image = imagecreatefromjpeg($filename); imagecopyresampled($image_p, $image, 0, 0, 0, 0, $width, $height, $width_orig, $height_orig); // Output imagejpeg($image_p, null, 100); ?>
There are two ways to change the image size:
- ImageCopyResized() function is valid in all GD versions, but its algorithm for scaling images is rough.
- ImageCopyResamples(), the image edges obtained by its pixel interpolation algorithm are relatively smooth. (But this function is slower than ImageCopyResized()).
The parameters of the two functions are the same, as follows:
imageCopyResampled(dest,src,dy,dx,sx,sy,dw,dh,sw,sh); imageCopyResized(dest,src,dy,dx,sx,sy,dw,dh,sw,sh);
Example:
<?PHP $src = ImageCreateFromJPEG('php.jpg'); $width = ImageSx($src); $height = ImageSy($src); $x = $widht/2; $y = $height/2; $dst = ImageCreateTrueColor($x,$y); ImageCopyResampled($dst,$src,0,0,0,0,$x,$y,$widht,$height); header('Content-Type : image/png'); ImagePNG($det); ?>

php把负数转为正整数的方法:1、使用abs()函数将负数转为正数,使用intval()函数对正数取整,转为正整数,语法“intval(abs($number))”;2、利用“~”位运算符将负数取反加一,语法“~$number + 1”。

实现方法:1、使用“sleep(延迟秒数)”语句,可延迟执行函数若干秒;2、使用“time_nanosleep(延迟秒数,延迟纳秒数)”语句,可延迟执行函数若干秒和纳秒;3、使用“time_sleep_until(time()+7)”语句。

php除以100保留两位小数的方法:1、利用“/”运算符进行除法运算,语法“数值 / 100”;2、使用“number_format(除法结果, 2)”或“sprintf("%.2f",除法结果)”语句进行四舍五入的处理值,并保留两位小数。

判断方法:1、使用“strtotime("年-月-日")”语句将给定的年月日转换为时间戳格式;2、用“date("z",时间戳)+1”语句计算指定时间戳是一年的第几天。date()返回的天数是从0开始计算的,因此真实天数需要在此基础上加1。

php字符串有下标。在PHP中,下标不仅可以应用于数组和对象,还可应用于字符串,利用字符串的下标和中括号“[]”可以访问指定索引位置的字符,并对该字符进行读写,语法“字符串名[下标值]”;字符串的下标值(索引值)只能是整数类型,起始值为0。

方法:1、用“str_replace(" ","其他字符",$str)”语句,可将nbsp符替换为其他字符;2、用“preg_replace("/(\s|\ \;||\xc2\xa0)/","其他字符",$str)”语句。

在php中,可以使用substr()函数来读取字符串后几个字符,只需要将该函数的第二个参数设置为负值,第三个参数省略即可;语法为“substr(字符串,-n)”,表示读取从字符串结尾处向前数第n个字符开始,直到字符串结尾的全部字符。

php判断有没有小数点的方法:1、使用“strpos(数字字符串,'.')”语法,如果返回小数点在字符串中第一次出现的位置,则有小数点;2、使用“strrpos(数字字符串,'.')”语句,如果返回小数点在字符串中最后一次出现的位置,则有。


Hot AI Tools

Undresser.AI Undress
AI-powered app for creating realistic nude photos

AI Clothes Remover
Online AI tool for removing clothes from photos.

Undress AI Tool
Undress images for free

Clothoff.io
AI clothes remover

AI Hentai Generator
Generate AI Hentai for free.

Hot Article

Hot Tools

Dreamweaver Mac version
Visual web development tools

VSCode Windows 64-bit Download
A free and powerful IDE editor launched by Microsoft

MinGW - Minimalist GNU for Windows
This project is in the process of being migrated to osdn.net/projects/mingw, you can continue to follow us there. MinGW: A native Windows port of the GNU Compiler Collection (GCC), freely distributable import libraries and header files for building native Windows applications; includes extensions to the MSVC runtime to support C99 functionality. All MinGW software can run on 64-bit Windows platforms.

PhpStorm Mac version
The latest (2018.2.1) professional PHP integrated development tool

SAP NetWeaver Server Adapter for Eclipse
Integrate Eclipse with SAP NetWeaver application server.
