使用 PHP 缩放图像并保持纵横比答案

【问题标题】：Scale Image Using PHP and Maintaining Aspect Ratio使用 PHP 缩放图像并保持纵横比
【发布时间】：2010-11-25 07:08:00
【问题描述】：

基本上我想上传一张图片（我已经排序）并将其缩小到某些限制，例如最大宽度和高度，但保持原始图片的纵横比。

我没有在服务器上安装 Imagick - 否则这很容易。

一如既往地感谢任何帮助。谢谢。

编辑：我不需要整个代码或任何东西，只要朝着正确的方向推进就很棒了。

【问题讨论】：

标签： php image scale

【解决方案1】：

这是我使用 X、Y 或两个轴保存纵横比来缩放图像的功能。

它还会将图像缩放到其大小的百分比。

兼容 PHP 5.4

/** Use X axis to scale image. */
define('IMAGES_SCALE_AXIS_X', 1);
/** Use Y axis to scale image. */
define('IMAGES_SCALE_AXIS_Y', 2);
/** Use both X and Y axes to calc image scale. */
define('IMAGES_SCALE_AXIS_BOTH', IMAGES_SCALE_AXIS_X ^ IMAGES_SCALE_AXIS_Y);
/** Compression rate for JPEG image format. */
define('JPEG_COMPRESSION_QUALITY', 90);
/** Compression rate for PNG image format. */
define('PNG_COMPRESSION_QUALITY', 9);

/**
 * Scales an image with save aspect ration for X, Y or both axes.
 *
 * @param string $sourceFile Absolute path to source image.
 * @param string $destinationFile Absolute path to scaled image.
 * @param int|null $toWidth Maximum `width` of scaled image.
 * @param int|null $toHeight Maximum `height` of scaled image.
 * @param int|null $percent Percent of scale of the source image's size.
 * @param int $scaleAxis Determines how of axis will be used to scale image.
 *
 * May take a value of {@link IMAGES_SCALE_AXIS_X}, {@link IMAGES_SCALE_AXIS_Y} or {@link IMAGES_SCALE_AXIS_BOTH}.
 * @return bool True on success or False on failure.
 */
function scaleImage($sourceFile, $destinationFile, $toWidth = null, $toHeight = null, $percent = null, $scaleAxis = IMAGES_SCALE_AXIS_BOTH) {
    $toWidth = (int)$toWidth;
    $toHeight = (int)$toHeight;
    $percent = (int)$percent;
    $result = false;

    if (($toWidth | $toHeight | $percent)
        && file_exists($sourceFile)
        && (file_exists(dirname($destinationFile)) || mkdir(dirname($destinationFile), 0777, true))) {

        $mime = getimagesize($sourceFile);

        if (in_array($mime['mime'], ['image/jpg', 'image/jpeg', 'image/pjpeg'])) {
            $src_img = imagecreatefromjpeg($sourceFile);
        } elseif ($mime['mime'] == 'image/png') {
            $src_img = imagecreatefrompng($sourceFile);
        }

        $original_width = imagesx($src_img);
        $original_height = imagesy($src_img);

        if ($scaleAxis == IMAGES_SCALE_AXIS_BOTH) {
            if (!($toWidth | $percent)) {
                $scaleAxis = IMAGES_SCALE_AXIS_Y;
            } elseif (!($toHeight | $percent)) {
                $scaleAxis = IMAGES_SCALE_AXIS_X;
            }
        }

        if ($scaleAxis == IMAGES_SCALE_AXIS_X && $toWidth) {
            $scale_ratio = $original_width / $toWidth;
        } elseif ($scaleAxis == IMAGES_SCALE_AXIS_Y && $toHeight) {
            $scale_ratio = $original_height / $toHeight;
        } elseif ($percent) {
            $scale_ratio = 100 / $percent;
        } else {
            $scale_ratio_width = $original_width / $toWidth;
            $scale_ratio_height = $original_height / $toHeight;

            if ($original_width / $scale_ratio_width < $toWidth && $original_height / $scale_ratio_height < $toHeight) {
                $scale_ratio = min($scale_ratio_width, $scale_ratio_height);
            } else {
                $scale_ratio = max($scale_ratio_width, $scale_ratio_height);
            }
        }

        $scale_width = $original_width / $scale_ratio;
        $scale_height = $original_height / $scale_ratio;

        $dst_img = imagecreatetruecolor($scale_width, $scale_height);

        imagecopyresampled($dst_img, $src_img, 0, 0, 0, 0, $scale_width, $scale_height, $original_width, $original_height);

        if (in_array($mime['mime'], ['image/jpg', 'image/jpeg', 'image/pjpeg'])) {
            $result = imagejpeg($dst_img, $destinationFile, JPEG_COMPRESSION_QUALITY);
        } elseif ($mime['mime'] == 'image/png') {
            $result = imagepng($dst_img, $destinationFile, PNG_COMPRESSION_QUALITY);
        }

        imagedestroy($dst_img);
        imagedestroy($src_img);
    }

    return $result;
}

测试：

$sourceFile = '/source/file.jpg'; // Original size: 672x100
$destinationPath = '/destination/path/';

scaleImage($sourceFile, $destinationPath . 'file_original_size.jpg', 672, 100);
// Result: Image 672x100
scaleImage($sourceFile, $destinationPath . 'file_scaled_75_PERCENT.jpg', null, null, 75);
// Result: Image 504x75
scaleImage($sourceFile, $destinationPath . 'file_scaled_336_X.jpg', 336, null, null, IMAGES_SCALE_AXIS_X);
// Result: Image 336x50
scaleImage($sourceFile, $destinationPath . 'file_scaled_50_Y.jpg', null, 50, null, IMAGES_SCALE_AXIS_Y);
// Result: Image 336x50
scaleImage($sourceFile, $destinationPath . 'file_scaled_500x70_BOTH.jpg', 500, 70, null, IMAGES_SCALE_AXIS_BOTH);
// Result: Image 470x70
scaleImage($sourceFile, $destinationPath . 'file_scaled_450x70_BOTH.jpg', 450, 70, null, IMAGES_SCALE_AXIS_BOTH);
// Result: Image 450x66
scaleImage($sourceFile, $destinationPath . 'file_scaled_500x70_40_PERCENT_BOTH.jpg', 500, 70, 40, IMAGES_SCALE_AXIS_BOTH);
// Result: Image 268x40

【讨论】：

很好，但这不会保留 PNG 的透明度。透明缩放：stackoverflow.com/a/279310/5078983

【解决方案2】：

非常适合我

    static function getThumpnail($file){

    $THUMBNAIL_IMAGE_MAX_WIDTH  = 150; # exmpl.
    $THUMBNAIL_IMAGE_MAX_HEIGHT = 150;

    $src_size = filesize($file);
    $filename = basename($file);

    list($src_width, $src_height, $src_type) = getimagesize($file);
    $src_im = false;
    switch ($src_type) {
        case IMAGETYPE_GIF  : $src_im = imageCreateFromGif($file);  break;
        case IMAGETYPE_JPEG : $src_im = imageCreateFromJpeg($file); break;
        case IMAGETYPE_PNG  : $src_im = imageCreateFromPng($file);  break;
        case IMAGETYPE_WBMP  : $src_im = imagecreatefromwbmp($file);  break;
    }   
    if ($src_im === false) { return false; }

    $src_aspect_ratio = $src_width / $src_height;
    $thu_aspect_ratio = $THUMBNAIL_IMAGE_MAX_WIDTH / $THUMBNAIL_IMAGE_MAX_HEIGHT;

    if ($src_width <= $THUMBNAIL_IMAGE_MAX_WIDTH && $src_height <= $THUMBNAIL_IMAGE_MAX_HEIGHT) {
        $thu_width  = $src_width;
        $thu_height = $src_height;
    } elseif ($thu_aspect_ratio > $src_aspect_ratio) {
        $thu_width  = (int) ($THUMBNAIL_IMAGE_MAX_HEIGHT * $src_aspect_ratio);
        $thu_height = $THUMBNAIL_IMAGE_MAX_HEIGHT;
    } else {
        $thu_width = $THUMBNAIL_IMAGE_MAX_WIDTH;
        $thu_height = (int) ($THUMBNAIL_IMAGE_MAX_WIDTH / $src_aspect_ratio);
    }

    $thu_im = imagecreatetruecolor($thu_width, $thu_height);
    imagecopyresampled($thu_im, $src_im, 0, 0, 0, 0, $thu_width, $thu_height, $src_width, $src_height);

    $dst_im    = imagecreatetruecolor($THUMBNAIL_IMAGE_MAX_WIDTH,$THUMBNAIL_IMAGE_MAX_WIDTH);
    $backcolor = imagecolorallocate($dst_im,192,192,192);
    imagefill($dst_im,0,0,$backcolor);
    imagecopy($dst_im, $thu_im, (imagesx($dst_im)/2)-(imagesx($thu_im)/2), (imagesy($dst_im)/2)-(imagesy($thu_im)/2), 0, 0, imagesx($thu_im), imagesy($thu_im));
    imagedestroy($src_im);
    imagedestroy($thu_im);
    }

【讨论】：

【解决方案3】：

我正在考虑如何实现这一点，我提出了一个非常好的解决方案，在任何情况下都可以使用...... 假设您想调整用户上传到您网站的重图像的大小，但您需要它来保持比例。所以我想出了这个：

<?php
// File 
$filename = 'test.jpg';



// Get sizes
list($width, $height) = getimagesize($filename);
//obtain ratio
$imageratio = $width/$height;

if($imageratio >= 1){
    $newwidth = 600;
    $newheight = 600 / $imageratio; 
}
else{
     $newidth = 400;
     $newheight = 400 / $imageratio;
};




// Load
$thumb = imagecreatetruecolor($newwidth, $newheight);
$source = imagecreatefromjpeg($filename);

// Resize
imagecopyresized($thumb, $source, 0, 0, 0, 0, $newwidth, $newheight, $width, 
$height);

// Output
imagejpeg($thumb, "img/test.jpg");
imagedestroy();
?>

在这种情况下，如果宽度大于高度，我希望宽度为 600px，如果高度大于宽度，我希望宽度为 400px

【讨论】：

【解决方案4】：

我找到了完成这项工作的数学方法

Github 存储库 - https://github.com/gayanSandamal/easy-php-image-resizer

现场示例 - https://plugins.nayague.com/easy-php-image-resizer/

<?php
//path for the image
$source_url = '2018-04-01-1522613288.PNG';

//separate the file name and the extention
$source_url_parts = pathinfo($source_url);
$filename = $source_url_parts['filename'];
$extension = $source_url_parts['extension'];

//define the quality from 1 to 100
$quality = 10;

//detect the width and the height of original image
list($width, $height) = getimagesize($source_url);
$width;
$height;

//define any width that you want as the output. mine is 200px.
$after_width = 200;

//resize only when the original image is larger than expected with.
//this helps you to avoid from unwanted resizing.
if ($width > $after_width) {

    //get the reduced width
    $reduced_width = ($width - $after_width);
    //now convert the reduced width to a percentage and round it to 2 decimal places
    $reduced_radio = round(($reduced_width / $width) * 100, 2);

    //ALL GOOD! let's reduce the same percentage from the height and round it to 2 decimal places
    $reduced_height = round(($height / 100) * $reduced_radio, 2);
    //reduce the calculated height from the original height
    $after_height = $height - $reduced_height;

    //Now detect the file extension
    //if the file extension is 'jpg', 'jpeg', 'JPG' or 'JPEG'
    if ($extension == 'jpg' || $extension == 'jpeg' || $extension == 'JPG' || $extension == 'JPEG') {
        //then return the image as a jpeg image for the next step
        $img = imagecreatefromjpeg($source_url);
    } elseif ($extension == 'png' || $extension == 'PNG') {
        //then return the image as a png image for the next step
        $img = imagecreatefrompng($source_url);
    } else {
        //show an error message if the file extension is not available
        echo 'image extension is not supporting';
    }

    //HERE YOU GO :)
    //Let's do the resize thing
    //imagescale([returned image], [width of the resized image], [height of the resized image], [quality of the resized image]);
    $imgResized = imagescale($img, $after_width, $after_height, $quality);

    //now save the resized image with a suffix called "-resized" and with its extension. 
    imagejpeg($imgResized, $filename . '-resized.'.$extension);

    //Finally frees any memory associated with image
    //**NOTE THAT THIS WONT DELETE THE IMAGE
    imagedestroy($img);
    imagedestroy($imgResized);
}
?>

【讨论】：

【解决方案5】：

我已经为我完成的另一个项目编写了一段这样的代码。我在下面复制了它，可能需要一些修补！（它确实需要 GD 库）

这些是它需要的参数：

$image_name - Name of the image which is uploaded
$new_width - Width of the resized photo (maximum)
$new_height - Height of the resized photo (maximum)
$uploadDir - Directory of the original image
$moveToDir - Directory to save the resized image

它将图像缩小或放大到最大宽度或高度

function createThumbnail($image_name,$new_width,$new_height,$uploadDir,$moveToDir)
{
    $path = $uploadDir . '/' . $image_name;

    $mime = getimagesize($path);

    if($mime['mime']=='image/png') { 
        $src_img = imagecreatefrompng($path);
    }
    if($mime['mime']=='image/jpg' || $mime['mime']=='image/jpeg' || $mime['mime']=='image/pjpeg') {
        $src_img = imagecreatefromjpeg($path);
    }   

    $old_x          =   imageSX($src_img);
    $old_y          =   imageSY($src_img);

    if($old_x > $old_y) 
    {
        $thumb_w    =   $new_width;
        $thumb_h    =   $old_y*($new_height/$old_x);
    }

    if($old_x < $old_y) 
    {
        $thumb_w    =   $old_x*($new_width/$old_y);
        $thumb_h    =   $new_height;
    }

    if($old_x == $old_y) 
    {
        $thumb_w    =   $new_width;
        $thumb_h    =   $new_height;
    }

    $dst_img        =   ImageCreateTrueColor($thumb_w,$thumb_h);

    imagecopyresampled($dst_img,$src_img,0,0,0,0,$thumb_w,$thumb_h,$old_x,$old_y); 


    // New save location
    $new_thumb_loc = $moveToDir . $image_name;

    if($mime['mime']=='image/png') {
        $result = imagepng($dst_img,$new_thumb_loc,8);
    }
    if($mime['mime']=='image/jpg' || $mime['mime']=='image/jpeg' || $mime['mime']=='image/pjpeg') {
        $result = imagejpeg($dst_img,$new_thumb_loc,80);
    }

    imagedestroy($dst_img); 
    imagedestroy($src_img);

    return $result;
}

【讨论】：

很好 - 非常感谢，这将很有用。我正在与主机交谈以尝试对 Imagick 进行排序...目前遇到一个致命错误，它说它没有找到该类...
如果您使用<?php phpinfo(); ?> 并搜索GD，如果启用，即使没有imagick，上述功能也应该可以工作:)，但是，如果您遇到任何错误，请随时让我知道。
不知道为什么这会引起投票，我几年前写的，最近在尝试（再次）解决相同问题时偶然发现它，但它没有保持纵横比！
当源图像不是正方形时，您肯定是指$thumb_h = $old_y*($new_width/$old_x); 和$thumb_w = $old_x*($new_height/$old_y);，这将始终调整为最大可能的缩略图，$new_height 作为最大高度，$new width 作为最大宽度
它几乎可以工作，但第二部分应该改为 if($old_x

【解决方案6】：

我知道您正在寻找可以按比例调整图像大小的除数。检查这个demo

如何在数学上得到除数

假设我们的原始图像具有宽度 x 和高度 y； x=300 和 y = 700

最大高度和最大宽度为200；

首先，我们将检查图像的哪个维度大于另一个。我们的高度（y）大于宽度（x）

其次，我们检查我们的高度是否大于我们的最大高度。对于我们的例子，我们的高度大于最大高度。在小于最大高度的情况下，我们将新高度设置为原始高度。

最后，我们寻找我们的除数，如下所示

if y is set to maximum height 200 and max-y=200;
y=max-y, that is 
if y=max-y
what about 
x=?
that is, 
if 700 is resized to 200
what about 300?
700=200
300=?
new width = (200 (new height) * 300(width)) / 700 (height)
so our divisor is
divisor= new height (300) / height(700) 
new width = divisor * width or width / (1/divisor)

如果宽度大于高度，反之亦然

if ($width > $height) {
    if($width < $max_width)
        $newwidth = $width;

    else

    $newwidth = $max_width; 


    $divisor = $width / $newwidth;
    $newheight = floor( $height / $divisor);
}
else {

     if($height < $max_height)
         $newheight = $height;
     else
         $newheight =  $max_height;

    $divisor = $height / $newheight;
    $newwidth = floor( $width / $divisor );
}

查看完整示例并使用working demo 进行尝试。

【讨论】：

我使用你的代码它可以工作，，，但是由于纵横比，这不提供 100*100 的图像，，这提供 100*50 的图像。如何添加背景颜色等图像的填充（25 up 和 25 btm）？

【解决方案7】：

这是一个综合性的应用程序，我努力开发它，包括最常见的操作，如放大和缩小、缩略图、保留纵横比、转换文件类型、更改质量/文件大小等等......

<?php
//##// Resize (and convert) image (Scale up & scale down, thumbnail, preserve aspect ratio) //##//
///////////////////////////////////////////////
///////////////// Begin.Setup /////////////////
// Source File:
$src_file = "/your/server/path/to/file.png";// png or jpg files only

// Resize Dimensions:
// leave blank for no size change (convert only)
// if you specify one dimension, the other dimension will be calculated according to the aspect ratio
// if you specify both dimensions system will take care of it depending on the actual image size 
// $newWidth = 2000;
// $newHeight = 1500;

// Destination Path: (optional, if none: download image)
$dst_path = "/your/server/path/new/";

// Destination File Name: (Leave blank for same file name)
// $dst_name = 'image_name_only_no_extension';

// Destination File Type: (Leave blank for same file extension)
// $dst_type = 'png';
$dst_type = 'jpg';

// Reduce to 8bit - 256 colors (Very low quality but very small file & transparent PNG. Only for thumbnails!)
// $palette_8bit = true;

///////////////// End.Setup /////////////////
///////////////////////////////////////////////
if (!$dst_name){$dst_name = strtolower(pathinfo($src_file, PATHINFO_FILENAME));}
if (!$dst_type){$dst_type = strtolower(pathinfo($src_file, PATHINFO_EXTENSION));}
if ($palette_8bit){$dst_type = 'png';}
if ($dst_path){$dst_file = $dst_path . $dst_name . '.' . $dst_type;}

$mime = getimagesize($src_file);// Get image dimensions and type

// Destination File Parameters:
if ($dst_type == 'png'){
    $dst_content = 'image/png';
    $quality = 9;// All same quality! 0 too big file // 0(no comp.)-9 (php default: 6)
} elseif ($dst_type == 'jpg'){
    $dst_content = 'image/jpg';
    $quality = 85;// 30 Min. 60 Mid. 85 Cool. 90 Max. (100 Full) // 0-100 (php default: 75)
} else {
    exit('Unknown Destination File Type');
}

// Source File Parameters:
if ($mime['mime']=='image/png'){$src_img = imagecreatefrompng($src_file);}
elseif ($mime['mime']=='image/jpg'){$src_img = imagecreatefromjpeg($src_file);}
elseif ($mime['mime']=='image/jpeg'){$src_img = imagecreatefromjpeg($src_file);}
elseif ($mime['mime']=='image/pjpeg'){$src_img = imagecreatefromjpeg($src_file);}
else {exit('Unknown Source File Type');}

// Define Dimensions:
$old_x = imageSX($src_img);
$old_y = imageSY($src_img);

if ($newWidth AND $newHeight){
    if($old_x > $old_y){
        $new_x    =   $newWidth;
        $new_y    =   $old_y / $old_x * $newWidth;
    } elseif($old_x < $old_y){
        $new_y    =   $newHeight;
        $new_x    =   $old_x / $old_y * $newHeight;
    } elseif($old_x == $old_y){
        $new_x    =   $newWidth;
        $new_y    =   $newHeight;
    }
} elseif ($newWidth){
    $new_x    =   $newWidth;
    $new_y    =   $old_y / $old_x * $newWidth;
} elseif ($newHeight){
    $new_y    =   $newHeight;
    $new_x    =   $old_x / $old_y * $newHeight;
} else {
    $new_x    =   $old_x;
    $new_y    =   $old_y;
}

$dst_img = ImageCreateTrueColor($new_x, $new_y);

if ($palette_8bit){//////// Reduce to 8bit - 256 colors ////////
    $transparent = imagecolorallocatealpha($dst_img, 255, 255, 255, 127); 
    imagecolortransparent($dst_img, $transparent);
    imagefill($dst_img, 0, 0, $transparent);
    imagecopyresampled($dst_img,$src_img,0,0,0,0,$new_x,$new_y,$old_x,$old_y);// Great quality resize.
    imagetruecolortopalette($dst_img, false, 255);
    imagesavealpha($dst_img, true);
} else {
    // Check image and set transparent for png or white background for jpg
    if ($dst_type == 'png'){
        imagealphablending($dst_img, false);
        imagesavealpha($dst_img, true);
        $transparent = imagecolorallocatealpha($dst_img, 255, 255, 255, 127);
        imagefilledrectangle($dst_img, 0, 0, $new_x, $new_y, $transparent);
    } elseif ($dst_type == 'jpg'){
        $white = imagecolorallocate($dst_img, 255, 255, 255);
        imagefilledrectangle($dst_img, 0, 0, $new_x, $new_y, $white);
    }

    imagecopyresampled($dst_img,$src_img,0,0,0,0,$new_x,$new_y,$old_x,$old_y);// Great quality resize.
}

// Skip the save to parameter using NULL, then set the quality; imagejpeg($dst_img);=> Default quality
if ($dst_file){
    if ($dst_type == 'png'){
        imagepng($dst_img, $dst_file, $quality);
    } elseif ($dst_type == 'jpg'){
        imagejpeg($dst_img, $dst_file, $quality);
    }
} else {
    header('Content-Disposition: Attachment;filename=' . $dst_name . '.' . $dst_type);// comment this line to show image in browser instead of download
    header('Content-type: ' . $dst_content);
    if ($dst_type == 'png'){
        imagepng($dst_img, NULL, $quality);
    } elseif ($dst_type == 'jpg'){
        imagejpeg($dst_img, NULL, $quality);
    }
}
imagedestroy($src_img);
imagedestroy($dst_img);
//##// END : Resize image (Scale Up & Down) (thumbnail, bigger image, preserve aspect ratio) END //##//

【讨论】：

这是一个非常高级的脚本，我努力涵盖最多并完善它。我注意到一个downvote，你真的尝试过吗？让我知道它是否有问题......
几年后，我用你的公式来保持纵横比和它的工作，赞成。关于整个 sn-p，我看不出有人投反对票的原因。谢谢。

【解决方案8】：

<?php
Class ResizedImage
{
    public $imgfile;
    public $string      = '';
    public $new_width   = 0;
    public $new_height  = 0;
    public $angle       = 0;
    public $max_font_size = 1000;
    public $cropped = false;//whether crop the original image if h or w > new h or w
    public $font = 'fonts/arialbd.ttf';

    private $img;
    private $trans_colour;
    private $orange;
    private $white; 
    private $whitetr;
    private $blacktr;

    public function PrintAsBase64()
    {
        $this->SetImage();
        ob_start();
        imagepng($this->img);
        $b64img = ob_get_contents();
        ob_clean();
        imagedestroy($this->img);
        $b64img = base64_encode($b64img);
        echo($b64img);
    }
    public function PrintAsImage()
    {
        $this->SetImage();

        header('Content-type: image/png');

        imagepng($this->img);
        imagedestroy($this->img);
    }

    private function SetImage()
    {
        if ($this->imgfile == '') {$this->imgfile='NoImageAvailable.jpg';}
        $this->img          = imagecreatefromstring(file_get_contents($this->imgfile));
        $this->trans_colour = imagecolorallocatealpha($this->img, 0, 0, 0, 127);
        $this->orange       = imagecolorallocate($this->img, 220, 210, 60);
        $this->white        = imagecolorallocate($this->img, 255,255, 255);
        $this->whitetr      = imagecolorallocatealpha($this->img, 255,255, 255, 95);
        $this->blacktr      = imagecolorallocatealpha($this->img, 0, 0, 0, 95);

        if ((!$this->cropped) && ($this->string !=''))
        {$this->watermarkimage();}

        if (($this->new_height > 0) && ($this->new_width > 0)) {$this->ResizeImage();};

        if (($this->cropped) && ($this->string !=''))
        {$this->watermarkimage();}

        imageAlphaBlending($this->img, true);
        imageSaveAlpha($this->img, true);
    }
    ////
    private function ResizeImage()
    {
        # v_fact and h_fact are the factor by which the original vertical / horizontal
        # image sizes should be multiplied to get the image to your target size.
        $v_fact = $this->new_height / imagesy($this->img);//target_height / im_height; 
        $h_fact = $this->new_width / imagesx($this->img);//target_width / im_width;
        # you want to resize the image by the same factor in both vertical 
        # and horizontal direction, so you need to pick the correct factor from
        # v_fact / h_fact so that the largest (relative to target) of the new height/width
        # equals the target height/width and the smallest is lower than the target.
        # this is the lowest of the two factors
        if($this->cropped) 
        {   $im_fact = max($v_fact, $h_fact);   }
        else
        {   $im_fact = min($v_fact, $h_fact);   }

        $new_height = round(imagesy($this->img) * $im_fact);
        $new_width  = round(imagesx($this->img) * $im_fact);

        $img2 = $this->img;     
        $this->img = imagecreatetruecolor($new_width, $new_height);     
        imagecopyresampled($this->img, $img2, 0, 0, 0, 0, $new_width, $new_height, imagesx($img2), imagesy($img2));

        $img2 = $this->img;     
        $this->img = imagecreatetruecolor($this->new_width, $this->new_height);
        imagefill($this->img, 0, 0, $this->trans_colour);

        $dstx = 0;
        $dsty = 0;
        if ($this->cropped)
        {
            if (imagesx($this->img) < imagesx($img2))
            {   $dstx = round((imagesx($this->img)-imagesx($img2))/2); }

            if (imagesy($this->img) < imagesy($img2))
            {   $dsty = round((imagesy($this->img)-imagesy($img2))/2); }
        }
        else
        {
            if (imagesx($this->img) > imagesx($img2))
            {   $dstx = round((imagesx($this->img)-imagesx($img2))/2); }

            if (imagesy($this->img) > imagesy($img2))
            {   $dsty = round((imagesy($this->img)-imagesy($img2))/2); }
        }

        imagecopy ( $this->img, $img2, $dstx, $dsty, 0, 0, imagesx($img2) , imagesy($img2));
        imagedestroy($img2);        
    }   

    ////

    private function calculateTextBox($text,$fontFile,$fontSize,$fontAngle) 
    { 
        /************ 
        simple function that calculates the *exact* bounding box (single pixel precision). 
        The function returns an associative array with these keys: 
        left, top:  coordinates you will pass to imagettftext 
        width, height: dimension of the image you have to create 
        *************/ 
        $rect = imagettfbbox($fontSize,$fontAngle,$fontFile,$text); 
        $minX = min(array($rect[0],$rect[2],$rect[4],$rect[6])); 
        $maxX = max(array($rect[0],$rect[2],$rect[4],$rect[6])); 
        $minY = min(array($rect[1],$rect[3],$rect[5],$rect[7])); 
        $maxY = max(array($rect[1],$rect[3],$rect[5],$rect[7])); 

        return array( 
        "left"   => abs($minX) - 1, 
        "top"    => abs($minY) - 1, 
        "width"  => $maxX - $minX, 
        "height" => $maxY - $minY,
        "box"    => $rect ); 
    }

    private function watermarkimage($font_size=0)
    {
        if ($this->string == '')
        {die('Watermark function call width empty string!');}

        $box = $this->calculateTextBox($this->string, $this->font, $font_size, $this->angle);
        while ( ($box['width'] < imagesx($this->img)) && ($box['height'] < imagesy($this->img)) && ($font_size <= $this->max_font_size) )
        {
            $font_size++;
            $box = $this->calculateTextBox($this->string, $this->font, $font_size, $this->angle);   
        }

        $font_size--;
        $box = $this->calculateTextBox($this->string, $this->font, $font_size, $this->angle);

        $vcenter = round((imagesy($this->img) / 2) + ($box['height'] / 2));  
        $hcenter = round((imagesx($this->img) - $box['width']) / 2 );

        imagettftext($this->img, $font_size, $this->angle, $hcenter, $vcenter, $this->blacktr, $this->font, $this->string);     
        imagettftext($this->img, $font_size, $this->angle, $hcenter+1, $vcenter-2, $this->whitetr, $this->font, $this->string);
    }
}
?>

我也一直在使用公认的答案，但在某些情况下它并没有保持这个比例。我在论坛上找到了一些很好的答案并将它们放在一起，最后创建了一个调整图像大小的类。作为额外功能，您可以添加水印文本。

你可以看到选择是否裁剪时会发生什么，如果没有，透明区域将添加到新调整大小的图像中。

这个例子比问的多，但我认为这是一个很好的例子。

【讨论】：

这似乎是一个很好的功能并且可以按预期工作，但是如果我想总是裁剪怎么办..例如我的目标图像是 500 400 那么：//W400 H300 = stretchW |拉伸H //W400 H500 = 首先拉伸W+H 然后裁剪H //W500 H300 = 首先拉伸W+H 然后裁剪W //W500 H500 = cropW |作物H
我没有清楚地理解您的意思，但是该功能有效。你可以选择裁剪或不裁剪。当您在页面上使用该功能时，将默认值设置为“true”。如果您可以通过一些更改使其更好地工作，欢迎您。顺便说一句，我不是 php/web master，只是一个业余爱好者。

【解决方案9】：

实际上被接受的解决方案不是正确的解决方案。原因很简单：会出现源图像和目标图像的比例不同的情况。任何计算都应反映这种差异。

请注意 PHP.net 网站上给出的示例中的相关行：

$ratio_orig = $width_orig/$height_orig;

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

完整的例子可以在这里找到： http://php.net/manual/en/function.imagecopyresampled.php

在 stackoverflow 上还有其他答案（带有示例），用于解决相同问题的类似问题（以不同方式表述的相同问题）。

例子：

假设我们有一个 1630 x 2400 像素的图像，我们希望自动调整其大小，同时保持纵横比为 160 x 240。让我们用公认的解决方案做一些数学运算：

if($old_x < $old_y) 
    {
        $thumb_w    =   $old_x*($new_width/$old_y);
        $thumb_h    =   $new_height;
    }

身高 = 240 宽度 = 1630 * ( 160/2400 ) = 1630 * 0.0666666666666667 = 108.6666666666667 108.6 x 240 这不是正确的解决方案。

提出的下一个解决方案如下：

if($old_x < $old_y)
    {
        $thumb_w    =   $old_x/$old_y*$newHeight;
        $thumb_h    =   $newHeight;
    }

高度 = 240; 宽度 = 1630 / 2400 * 240 = 163 它更好（因为它保持纵横比），但它超过了可接受的最大宽度。

都失败了。

我们根据 PHP.net 提出的解决方案进行数学计算：宽度 = 160 高度 = 160/(1630 / 2400) = 160/0.6791666666666667 = 235.5828220858896（else 子句）。 160 x 236（四舍五入）是正确答案。

【讨论】：

【解决方案10】：

公式在保持纵横比方面是错误的。应该是：原始高度/原始宽度x新宽度=新高度

function createThumbnail($imageName,$newWidth,$newHeight,$uploadDir,$moveToDir)
{
    $path = $uploadDir . '/' . $imageName;

    $mime = getimagesize($path);

    if($mime['mime']=='image/png'){ $src_img = imagecreatefrompng($path); }
    if($mime['mime']=='image/jpg'){ $src_img = imagecreatefromjpeg($path); }
    if($mime['mime']=='image/jpeg'){ $src_img = imagecreatefromjpeg($path); }
    if($mime['mime']=='image/pjpeg'){ $src_img = imagecreatefromjpeg($path); }

    $old_x = imageSX($src_img);
    $old_y = imageSY($src_img);

    if($old_x > $old_y)
    {
        $thumb_w    =   $newWidth;
        $thumb_h    =   $old_y/$old_x*$newWidth;
    }

    if($old_x < $old_y)
    {
        $thumb_w    =   $old_x/$old_y*$newHeight;
        $thumb_h    =   $newHeight;
    }

    if($old_x == $old_y)
    {
        $thumb_w    =   $newWidth;
        $thumb_h    =   $newHeight;
    }

    $dst_img        =   ImageCreateTrueColor($thumb_w,$thumb_h);

    imagecopyresampled($dst_img,$src_img,0,0,0,0,$thumb_w,$thumb_h,$old_x,$old_y);


    // New save location
    $new_thumb_loc = $moveToDir . $imageName;

    if($mime['mime']=='image/png'){ $result = imagepng($dst_img,$new_thumb_loc,8); }
    if($mime['mime']=='image/jpg'){ $result = imagejpeg($dst_img,$new_thumb_loc,80); }
    if($mime['mime']=='image/jpeg'){ $result = imagejpeg($dst_img,$new_thumb_loc,80); }
    if($mime['mime']=='image/pjpeg'){ $result = imagejpeg($dst_img,$new_thumb_loc,80); }

    imagedestroy($dst_img);
    imagedestroy($src_img);
    return $result;
}

【讨论】：

只是，它不保持纵横比。如果我想将 300x300 的图像调整为 500x200，它将创建一个 500x200。