如何在 PHP 中调整透明的 png 大小？

How do I resize pngs with transparency in PHP?

提问by Ryan Doherty

I'm attempting to resize pngs with transparent backgrounds in PHP and the code samples I've found online don't work for me. Here's the code I'm using, advice will be much appreciated!

我正在尝试在 PHP 中调整具有透明背景的 png 的大小，而我在网上找到的代码示例对我不起作用。这是我正在使用的代码，非常感谢您的建议！

$this->image = imagecreatefrompng($filename);

imagesavealpha($this->image, true);
$newImage = imagecreatetruecolor($width, $height);

// Make a new transparent image and turn off alpha blending to keep the alpha channel
$background = imagecolorallocatealpha($newImage, 255, 255, 255, 127);
imagecolortransparent($newImage, $background);
imagealphablending($newImage, false);
imagesavealpha($newImage, true);

imagecopyresampled($newImage, $this->image, 0, 0, 0, 0, $width, $height,  $this->getWidth(), $this->getHeight());
$this->image = $newImage;  
imagepng($this->image,$filename);

UpdateBy 'not working' I meant to say the background color changes to black when I resize pngs.

更新'不工作' 我的意思是说当我调整 png 大小时背景颜色变为黑色。

回答by Dycey

From what I can tell, you need to set the blending mode to false, and the save alpha channel flag to truebeforeyou do the imagecolorallocatealpha()

据我所知，在执行 imagecolorallocatealpha()之前，您需要将混合模式设置为false，并将保存 alpha 通道标志设置为true

<?php
/**
 * https://stackoverflow.com/a/279310/470749
 * 
 * @param resource $image
 * @param int $newWidth
 * @param int $newHeight
 * @return resource
 */
public function getImageResized($image, int $newWidth, int $newHeight) {
    $newImg = imagecreatetruecolor($newWidth, $newHeight);
    imagealphablending($newImg, false);
    imagesavealpha($newImg, true);
    $transparent = imagecolorallocatealpha($newImg, 255, 255, 255, 127);
    imagefilledrectangle($newImg, 0, 0, $newWidth, $newHeight, $transparent);
    $src_w = imagesx($image);
    $src_h = imagesy($image);
    imagecopyresampled($newImg, $image, 0, 0, 0, 0, $newWidth, $newHeight, $src_w, $src_h);
    return $newImg;
}
?>

UPDATE: This code is working only on background transparent with opacity = 0. If your image have 0 < opacity < 100 it'll be black background.

更新：此代码仅适用于不透明度 = 0 的背景透明。如果您的图像具有 0 < 不透明度 < 100，它将是黑色背景。

回答by Michael

Here is a final solution that is working fine for me.

这是一个对我来说很好的最终解决方案。

function resizePng($im, $dst_width, $dst_height) {
    $width = imagesx($im);
    $height = imagesy($im);

    $newImg = imagecreatetruecolor($dst_width, $dst_height);

    imagealphablending($newImg, false);
    imagesavealpha($newImg, true);
    $transparent = imagecolorallocatealpha($newImg, 255, 255, 255, 127);
    imagefilledrectangle($newImg, 0, 0, $width, $height, $transparent);
    imagecopyresampled($newImg, $im, 0, 0, 0, 0, $dst_width, $dst_height, $width, $height);

    return $newImg;
}

回答by jTresidder

The filling of the new image with a transparent colour is also required (as Dycey coded but I'm guessing forgot to mention :)), not just the 'strategic' saving by itself.

还需要用透明颜色填充新图像（如 Dycey 编码，但我猜忘了提及:)），而不仅仅是“战略”保存本身。

IIRC, you also need to be sure PNGs are 24bit, ie truecolor, and not 8bit to avoid buggy behaviour.

IIRC，您还需要确保 PNG 是 24 位，即真彩色，而不是 8 位以避免错误行为。

回答by sbeam

old thread, but just in case - Dycey's example should work, if you name things correctly. Here is a modified version used in my image resizing class. Notice the check to make sure imagecolorallocatealpha() is defined, which it won't be if you are using GD <2.0.8

旧线程，但以防万一 - 如果您正确命名，Dycey 的示例应该可以工作。这是我的图像大小调整类中使用的修改版本。请注意检查以确保定义了 imagecolorallocatealpha()，如果您使用 GD <2.0.8，则不会

  /**
     * usually when people use PNGs, it's because they need alpha channel 
     * support (that means transparency kids). So here we jump through some 
     * hoops to create a big transparent rectangle which the resampled image 
     * will be copied on top of. This will prevent GD from using its default 
     * background, which is black, and almost never correct. Why GD doesn't do 
     * this automatically, is a good question.
     *
     * @param $w int width of target image
     * @param $h int height of target image
     * @return void
     * @private
     */
    function _preallocate_transparency($w, $h) {
        if (!empty($this->filetype) && !empty($this->new_img) && $this->filetype == 'image/png')) {
            if (function_exists('imagecolorallocatealpha')) {
                imagealphablending($this->new_img, false);
                imagesavealpha($this->new_img, true);
                $transparent = imagecolorallocatealpha($this->new_img, 255, 255, 255, 127);
                imagefilledrectangle($this->new_img, 0, 0, $tw, $th, $transparent);
            }
        }
    }

回答by Capsule

It's probably related to the newer versions of PHP (I tested with PHP 5.6) but this now works without the need to fill the image with a transparent background:

它可能与较新版本的 PHP（我用 PHP 5.6 测试过）有关，但现在无需使用透明背景填充图像即可工作：

$image_p = imagecreatetruecolor(480, 270);
imageAlphaBlending($image_p, false);
imageSaveAlpha($image_p, true);
$image = imagecreatefrompng('image_with_some_transaprency.png');
imagecopyresampled($image_p, $image, 0, 0, 0, 0, 480, 270, 1920, 1080);
imagepng($image_p, 'resized.png', 0);

回答by Alexandr

this is also not working for me :( thisis my solution.. but i also get a black background and the image is not transparent

这对我也不起作用:(这是我的解决方案..但我也得到了黑色背景并且图像不透明

    <?php
$img_id = 153;

$source = "images/".$img_id.".png";
$source = imagecreatefrompng($source);
$o_w = imagesx($source);
$o_h = imagesy($source);

$w = 200;
$h = 200;

$newImg = imagecreatetruecolor($w, $h);
imagealphablending($newImg, false);
imagesavealpha($newImg,true);
$transparent = imagecolorallocatealpha($newImg, 255, 255, 255, 127);
imagefilledrectangle($newImg, 0, 0, $w, $h, $transparent);
imagecopyresampled($newImg, $source, 0, 0, 0, 0, $w, $h, $o_w, $o_h);

imagepng($newImg, $img_id.".png");

?>
<img src="<?php echo $img_id.".png" ?>" />

回答by Don Vaidoso

Full example. Notice that for some png images found on internet it works incorrect, but for my own created with photoshop it works fine.

完整的例子。请注意，对于在 Internet 上找到的某些 png 图像，它无法正常工作，但对于我自己使用 photoshop 创建的图像，它可以正常工作。

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

$filename = "url to some image";

$newWidth = 300;
$newHeight = 300;

$imageInfo = getimagesize($filename);

$image = imagecreatefrompng($filename); //create source image resource
imagesavealpha($image, true); //saving transparency

$newImg = imagecreatetruecolor($newWidth, $newHeight); //creating conteiner for new image
imagealphablending($newImg, false);
imagesavealpha($newImg,true);
$transparent = imagecolorallocatealpha($newImg, 255, 255, 255, 127); //seting transparent background
imagefilledrectangle($newImg, 0, 0, $newWidth, $newHeight, $transparent);
imagecopyresampled($newImg, $image, 0, 0, 0, 0, $newWidth, $newHeight,  $imageInfo[0], $imageInfo[1]);

imagepng($newImg); //printout image string

回答by Kaushal Sachan

Here is full code working for png files with preserving their images transparency..

这是适用于 png 文件并保留其图像透明度的完整代码..

list($width, $height) = getimagesize($filepath);
$new_width = "300";
$new_height = "100";

if($width>$new_width && $height>$new_height)
{
    $image_p = imagecreatetruecolor($new_width, $new_height);
    imagealphablending($image_p, false);
    imagesavealpha($image_p, true);
    $image = imagecreatefrompng($filepath);
    imagecopyresampled($image_p, $image, 0, 0, 0, 0, $new_width, $new_height, $width, $height);
    imagepng($image_p,$filepath,5);
}

回答by arc_shiva

Nor the above solution worked for me. This is the way what i found out to solve the issue.

上述解决方案也不适合我。这是我发现解决问题的方法。

// upload directory
$upload_dir = "../uploads/";
// valid image formats
$valid_formats = array("jpg", "jpeg", "png");
// maximum image size 1 mb
$max_size = 1048576;
// crop image width, height
$nw = $nh = 800;
$nw1 = $nh1 = 400;
$nw3 = $nh3 = 200;
$nw2 = $nh2 = 100;
// checks that if upload_dir a directory/not
if (is_dir($upload_dir) && is_writeable($upload_dir)) {
    // not empty file
    if (!empty($_FILES['image'])) {
        // assign file name 
        $name = $_FILES['image']['name'];
        // $_FILES to execute all files within a loop
        if ($_FILES['image']['error'] == 4) {
            $message = "Empty FIle";
        }
        if ($_FILES['image']['error'] == 0) {
            if ($_FILES['image']['size'] > $max_size) {
                echo "E-Image is too large!<br>";
                $_SESSION['alert'] = "Image is too large!!";
            } else if (!in_array(pathinfo($name, PATHINFO_EXTENSION), $valid_formats)) {
                $_SESSION['alert'] = "This image is not a valid image format!!";
                echo "E-This image is not a valid image format<br>";
            } else if (file_exists($upload_dir . $name)) {
                $_SESSION['alert'] = "Image already exists!!";
                echo "E-Image already exists<br>";
            } else { // No error found! Move uploaded files 
                $size = getimagesize($_FILES['image']['tmp_name']);
                $x = (int) $_POST['x'];
                $y = (int) $_POST['y'];
                $w = (int) $_POST['w'] ? $_POST['w'] : $size[0];
                $h = (int) $_POST['h'] ? $_POST['h'] : $size[1];
                // path for big image
                $big_image_path = $upload_dir . "big/" . $name;
                // medium image path
                $medium_image_path = $upload_dir . "medium/" . $name;
                // small image path
                $small_image_path = $upload_dir . "small/" . $name;
                // check permission
                if (!is_dir($upload_dir . "big/") && !is_writeable($upload_dir . "big/")) {
                    mkdir($upload_dir . "big/", 0777, false);
                }
                if (!is_dir($upload_dir . "medium/") && !is_writeable($upload_dir . "medium/")) {
                    mkdir($upload_dir . "medium/", 0777, false);
                }
                if (!is_dir($upload_dir . "small/") && !is_writeable($upload_dir . "small/")) {
                    mkdir($upload_dir . "small/", 0777, false);
                }
                // image raw data from form
                $data = file_get_contents($_FILES["image"]["tmp_name"]);
                // create image
                $vImg = imagecreatefromstring($data);
                //create big image
                $dstImg = imagecreatetruecolor($nw, $nh);
                imagealphablending($dstImg, false);
                $trans_colour = imagecolorallocatealpha($dstImg, 0, 0, 0, 127);
                imagefilledrectangle($dstImg, 0, 0, $w, $h, $trans_colour);
                imagesavealpha($dstImg, true);
                imagecopyresampled($dstImg, $vImg, 0, 0, $x, $y, $nw, $nh, $w, $h);
                imagepng($dstImg, $big_image_path);
                //create medium thumb
                $dstImg1 = imagecreatetruecolor($nw1, $nh1);
                imagealphablending($dstImg1, false);
                $trans_colour1 = imagecolorallocatealpha($dstImg1, 0, 0, 0, 127);
                imagefilledrectangle($dstImg1, 0, 0, $w, $h, $trans_colour1);
                imagesavealpha($dstImg1, true);
                imagecopyresampled($dstImg1, $vImg, 0, 0, $x, $y, $nw1, $nh1, $w, $h);
                imagepng($dstImg1, $medium_image_path);
                // create smallest thumb
                $dstImg2 = imagecreatetruecolor($nw2, $nh2);
                imagealphablending($dstImg2, false);
                $trans_colour2 = imagecolorallocatealpha($dstImg2, 0, 0, 0, 127);
                imagefilledrectangle($dstImg2, 0, 0, $w, $h, $trans_colour2);
                imagesavealpha($dstImg2, true);
                imagecopyresampled($dstImg2, $vImg, 0, 0, $x, $y, $nw2, $nh2, $w, $h);
                imagepng($dstImg2, $small_image_path);
                /*
                 * Database insertion
                 */
                $sql = "INSERT INTO tbl_inksand_product_gallery ("
                        . "Product_Id,Gallery_Image_Big,Gallery_Image_Medium,Gallery_Image_Thumb,"
                        . "Gallery_Status,Created_By,Created_Datetime"
                        . ") VALUES ("
                        . "'{$Product_Id}','{$big_image_path}','{$medium_image_path}','{$small_image_path}',"
                        . "'A','$Created_By','{$time}'"
                        . ")";
                db_query($sql);
                if (db_affected_rows() == 1) {
                    if (imagedestroy($dstImg)) {
                        $_SESSION['success'] = "Image uploaded successfully.";
                        echo "S-Image uploaded successfully<br>";
                    } else {
                        $_SESSION['alert'] = "Image not uploaded!!";
                        echo "S-Image not uploaded";
                    }
                } else {
                    $_SESSION['alert'] = "Error in uploading image!!";
                    echo "E-Error in uploading image!!";
                }
            }
        }
    }
} else {
    mkdir($upload_dir, 0777);
}

回答by hkiame

using imagescale is better compared to imagecopyresampled. No empty image resource required for the resized image, requires only two arguments compared to the ten required by imagecopyresampled. Also produces better quality with smaller sizes. If using PHP 5.5.18 or earlier, or PHP 5.6.2 or earlier, you should provide the height which is the 3rd argument as the aspect ratio calculation was incorrect.

与 imagecopyresampled 相比，使用 imagescale 更好。调整大小的图像不需要空图像资源，与 imagecopyresampled 所需的十个参数相比，只需要两个参数。还可以用更小的尺寸生产更好的质量。如果使用 PHP 5.5.18 或更早版本，或者 PHP 5.6.2 或更早版本，您应该提供作为第三个参数的高度，因为纵横比计算不正确。

$this->image =   imagecreatefrompng($filename);
$scaled = imagescale($this->image, $width);
imagealphablending($scaled, false);
imagesavealpha($scaled, true);
imagepng($scaled, $filename);