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

yum install php-gd

2.重启web服务器

service httpd restart

3.查看PHP支持的GD库版本

php -i | grep -i gd

在Ubuntu/Debian下安装GD库

1.安装php5-gd模块

apt-get ｕｐｄａｔｅ && apt-get install php5-gd

2.重启web服务器

service apache2 restart

3.查看PHP支持的GD库版本

php -i | grep -i gd

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,$white,'',$text);

3）保存图像到文件
imagepng($image,'');

4）释放内存
imagedestroy($image);

2.图像处理

1）缩放图像
$src_image = imagecreatefrompng('');
$src_width = imagesx($src_image);
$src_height = imagesy($src_image);
$new_width = $src_width * ;
$new_height = $src_height * ;
$new_image = imagecreatetruecolor($new_width,$new_height);
imagecopyresampled($new_image,$src_image,0,0,0,0,$new_width,$new_height,$src_width,$src_height);
imagepng($new_image,'');

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,'');

3）裁剪图像
$cropped_image = imagecrop($new_image,['x'=>40,'y'=>40,'width'=>100,'height'=>100]);
imagepng($cropped_image,'');

4）模糊图像
$blurred_image = imagefilter($new_image,IMG_FILTER_GAUSSIAN_BLUR);
imagepng($blurred_image,'');

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,'');

3）填充图像
$fill_color = imagecolorallocate($new_image,0,255,0);
imagefill($new_image,0,0,$fill_color);
imagepng($new_image,'');

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,$font_color,'',$watermark_text);
imagepng($new_image,'');

2）添加图片水印
$watermark_image = imagecreatefrompng('');
$watermark_width = imagesx($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,'');

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,'');

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,'');

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 * ;
$circle_radius = $circle_diameter / 2;
imageellipse($new_image,$circle_center_x,$circle_center_y,$circle_diameter,$circle_diameter,$circle_color);
imagepng($new_image,'');