一、GD库简介
GD库是PHP的一个扩展库，用于生成和编辑图像。它支持多种图像格式，包括GIF、JPEG、PNG等。要使用GD库，首先需要确保PHP安装了GD扩展。
1. 检测GD库支持类型
$gd_info = gd_info();
echo "<pre>";
print_r($gd_info);
echo "</pre>";
2. GD库版本信息
$gd_info['GD Version']将返回GD库的版本信息。
二、图片生成
1. 创建空白图片
$im = imagecreatetruecolor(100, 50);
2. 设置背景颜色
$background_color = imagecolorallocate($im, 255, 255, 255);
imagefill($im, 0, 0, $background_color);
3. 输出图片
header('Content-Type: image/png');
imagepng($im);
imagedestroy($im);
三、图片处理
1. 图片裁剪
$source_image = imagecreatefromjpeg('source.jpg');
$destination_image = imagecreatetruecolor(100, 100);
imagecopyresampled($destination_image, $source_image, 0, 0, 50, 50, 100, 100, 200, 200);
imagepng($destination_image, 'destination.jpg');
imagedestroy($destination_image);
2. 图片压缩
$source_image = imagecreatefromjpeg('source.jpg');
imagejpeg($source_image, 'destination.jpg', 50); // 质量参数为50
imagedestroy($source_image);
3. 图片添加水印
$source_image = imagecreatefromjpeg('source.jpg');
$watermark_image = imagecreatefrompng('watermark.png');
imagealphablending($source_image, true);
imagecopy($source_image, $watermark_image, 10, 10, 0, 0, imagesx($watermark_image), imagesy($watermark_image));
imagepng($source_image, 'source_with_watermark.jpg');
imagedestroy($source_image);
四、图片信息获取
$source_image = imagecreatefromjpeg('source.jpg');
$image_info = getimagesize($source_image);
echo "Width: " . $image_info[0] . "<br>";
echo "Height: " . $image_info[1] . "<br>";
echo "Type: " . $image_info[2] . "<br>";
echo "Size: " . $image_info[3] . "<br>";
imagedestroy($source_image);