一、什么是GD库？
GD库是一组用于创建和处理各种图像格式的库函数，是PHP中最为常用的图像处理库之一。
二、安装GD库
在CentOS/RedHat下安装GD库
1.安装PHP的GD扩展库
2.重启web服务器
3.查看PHP支持的GD库版本
在Ubuntu/Debian下安装GD库
1.安装php5-gd模块
2.重启web服务器
3.查看PHP支持的GD库版本
三、GD库的基本操作
1.创建图像
1）创建一个200X200像素的黑色图像
$image = imagecreate(200,200);
$black = imagecolorallocate($image,0,0,0);
imagefill($image,0,0,$black);
2）在图像中添加文本
$white = imagecolorallocate($image,255,255,255);
$text = 'Hello, GD!';
imagettftext($image,20,0,70,100,$white,'arial.ttf',$text);
3）保存图像到文件
imagepng($image,'test.png');
4）释放内存
imagedestroy($image);
2.图像处理
1）缩放图像
$src_image = imagecreatefrompng('test.png');
$src_width = imagesx($src_image);
$src_height = imagesy($src_image);
$new_width = $src_width * 0.5;
$new_height = $src_height * 0.5;
$new_image = imagecreatetruecolor($new_width,$new_height);
imagecopyresampled($new_image,$src_image,0,0,0,0,$new_width,$new_height,$src_width,$src_height);
imagepng($new_image,'test-resized.png');
2）添加边框
$border_color = imagecolorallocate($new_image,128,128,128);
imagerectangle($new_image,0,0,$new_width-1,$new_height-1,$border_color);
imagepng($new_image,'test-bordered.png');
3）裁剪图像
$cropped_image = imagecrop($new_image,['x'=>40,'y'=>40,'width'=>100,'height'=>100]);
imagepng($cropped_image,'test-cropped.png');
4）模糊图像
$blurred_image = imagefilter($new_image,IMG_FILTER_GAUSSIAN_BLUR);
imagepng($blurred_image,'test-blurred.png');
3.操作图像元素
1）获取像素RGB值
$pixel = imagecolorat($new_image,50,50);
$red = ($pixel >> 16) & 0xFF;
$green = ($pixel >> 8) & 0xFF;
$blue = $pixel & 0xFF;
2）修改像素RGB值
$new_color = imagecolorallocate($new_image,255,0,0);
imagesetpixel($new_image,50,50,$new_color);
imagepng($new_image,'test-pixel.png');
3）填充图像
$fill_color = imagecolorallocate($new_image,0,255,0);
imagefill($new_image,0,0,$fill_color);
imagepng($new_image,'test-filled.png');
四、GD库的高级操作
1.水印处理
1）添加文字水印
$watermark_text = 'COPYRIGHT';
$font_size = 20;
$font_color = imagecolorallocate($new_image,0,0,0);
imagettftext($new_image,$font_size,0,10,20,$font_color,'arial.ttf',$watermark_text);
imagepng($new_image,'test-watermark.png');
2）添加图片水印
$watermark_image = imagecreatefrompng('watermark.png');
$watermark_width = imagesx($watermark_image);
$watermark_height = imagesy($watermark_image);
$pos_x = ($new_width - $watermark_width) / 2;
$pos_y = ($new_height - $watermark_height) / 2;
imagecopy($new_image,$watermark_image,$pos_x,$pos_y,0,0,$watermark_width,$watermark_height);
imagepng($new_image,'test-watermark.png');
2.画图操作
1）画直线
$line_color = imagecolorallocate($new_image,0,0,255);
imageline($new_image,0,0,$new_width,$new_height,$line_color);
imagepng($new_image,'test-line.png');
2）画矩形
$rect_color = imagecolorallocate($new_image,0,255,0);
imagerectangle($new_image,20,20,$new_width-20,$new_height-20,$rect_color);
imagepng($new_image,'test-rectangle.png');
3）画圆形
$circle_color = imagecolorallocate($new_image,255,0,0);
$circle_center_x = $new_width/2;
$circle_center_y = $new_height/2;
$circle_diameter = $new_height * 0.8;
$circle_radius = $circle_diameter / 2;
imageellipse($new_image,$circle_center_x,$circle_center_y,$circle_diameter,$circle_diameter,$circle_color);
imagepng($new_image,'test-circle.png');
五、总结
本文介绍了GD库的基本操作和高级操作，包括图像创建、图像处理、操作图像元素、水印处理、画图操作等内容。GD库是PHP开发中非常实用的图像处理工具之一，可以用于制作图片验证码、生成二维码、图表、海报等。掌握GD库的使用技能可以帮助PHP开发者更加高效地完成业务需求。
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