How to change the size of an image with PHP_PHP Tutorial-PHP Tutorial-php.cn

How to change the size of an image with PHP_PHP Tutorial

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Release： 2016-07-13 10:33:01

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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);
}
?>

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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);
?>

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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);
?>

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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);

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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);
?>

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