一副1024*768大小的图片，裁剪到240*240大小，裁剪后不失真，尽可能保留图片主题含义。
我使用到的方法：
1. 先将图片等比例缩略到可以裁剪的大小；
如果是宽幅图片，则按高度等比例缩放到高度 = 240px，窄幅图片（高度大于宽度）则按宽度等比例缩放；
2. 按长宽格式居中裁剪；
保留缩略后的图片中间部分；
代码如下:
$this->load->library('image_lib');
list($width,$height) = getimagesize("upload/123.jpg");
$config['image_library'] = 'gd2';
$config['source_image'] = 'upload/123.jpg';
$config['maintain_ratio'] = TRUE;
if($width >= $height)
{
$config['master_dim'] = 'height';
}else{
$config['master_dim'] = 'width';
}
$config['width'] = 240;
$config['height'] = 240;
$this->image_lib->initialize($config);
$this->image_lib->resize(); $config['maintain_ratio'] = FALSE;
if($width >= $height)
{
$config['x_axis'] = floor(($width * 240 / $height - 240)/2);
}else{
$config['y_axis'] = floor(($height * 240 / $width - 240)/2);
}
$this->image_lib->initialize($config);
$this->image_lib->crop();
list($width,$height) = getimagesize("upload/123.jpg");
$config['image_library'] = 'gd2';
$config['source_image'] = 'upload/123.jpg';
$config['maintain_ratio'] = TRUE;
if($width >= $height)
{
$config['master_dim'] = 'height';
}else{
$config['master_dim'] = 'width';
}
$config['width'] = 240;
$config['height'] = 240;
$this->image_lib->initialize($config);
$this->image_lib->resize(); $config['maintain_ratio'] = FALSE;
if($width >= $height)
{
$config['x_axis'] = floor(($width * 240 / $height - 240)/2);
}else{
$config['y_axis'] = floor(($height * 240 / $width - 240)/2);
}
$this->image_lib->initialize($config);
$this->image_lib->crop();
