PHP GD2：如何保持alpha通道透明度和正确的gamma
我对图像缩放的讨论很感兴趣，后来发现我用来从上传的图像创建缩略图的PHP代码遇到了同样的问题。我决定尝试在底部附近发布的PHP修补程序（将伽玛值从2.2转换为1.0，调整图像大小，将伽玛值从1.0转换回2.2）。这有助于解决文章中提到的问题，但是对代码的这种修改具有淘汰PNG alpha通道透明度的不幸副作用。
这是我对伽马校正的代码。
<?php
$image = imagecreatefrompng($source_file);
$resized_image = imagecreatetruecolor($new_width, $new_height);
imagealphablending($resized_image, false);
imagesavealpha($resized_image, true);
imagegammacorrect($image, 2.2, 1.0);
imagecopyresampled($resized_image, $image, 0, 0, 0, 0, $new_width, $new_height, $image_width, $image_height);
imagegammacorrect($resized_image, 1.0, 2.2);
imagepng($resized_image, $dest_file);
?>
没有找到相关结果
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癸痊醒
<?php // Load image $image = imagecreatefrompng('test-image.png'); // Create destination $resized_image = imagecreatetruecolor(100, 100); imagealphablending($resized_image, false); // Overwrite alpha imagesavealpha($resized_image, true); // Create a separate alpha channel $alpha_image = imagecreatetruecolor(200, 200); imagealphablending($alpha_image, false); // Overwrite alpha imagesavealpha($alpha_image, true); for ($x = 0; $x < 200; $x++) { for ($y = 0; $y < 200; $y++) { $alpha = (imagecolorat($image, $x, $y) >> 24) & 0xFF; $color = imagecolorallocatealpha($alpha_image, 0, 0, 0, $alpha); imagesetpixel($alpha_image, $x, $y, $color); } } // Resize image to destination, using gamma correction imagegammacorrect($image, 2.2, 1.0); imagecopyresampled($resized_image, $image, 0, 0, 0, 0, 100, 100, 200, 200); imagegammacorrect($resized_image, 1.0, 2.2); // Resize alpha channel $alpha_resized_image = imagecreatetruecolor(200, 200); imagealphablending($alpha_resized_image, false); imagesavealpha($alpha_resized_image, true); imagecopyresampled($alpha_resized_image, $alpha_image, 0, 0, 0, 0, 100, 100, 200, 200); // Copy alpha channel back to resized image for ($x = 0; $x < 100; $x++) { for ($y = 0; $y < 100; $y++) { $alpha = (imagecolorat($alpha_resized_image, $x, $y) >> 24) & 0xFF; $rgb = imagecolorat($resized_image, $x, $y); $r = ($rgb >> 16 ) & 0xFF; $g = ($rgb >> 8 ) & 0xFF; $b = $rgb & 0xFF; $color = imagecolorallocatealpha($resized_image, $r, $g, $b, $alpha); imagesetpixel($resized_image, $x, $y, $color); } } imagepng($resized_image, 'test-image-scaled.png'); ?>烷刨画颠离