(PHP 7 >= 7.2.0)
imageresolution — Get or set the resolution of the image
imageresolution() allows to set and get the resolution of
an image in DPI (dots per inch). If none of the optional parameters is given,
the current resolution is returned as indexed array. If only
res_x is given, the horizontal and vertical resolution
are set to this value. If both optional parameters are given, the horizontal
and vertical resolution are set to these values, respectively.
The resolution is only used as meta information when images are read from and written to formats supporting this kind of information (curently PNG and JPEG). It does not affect any drawing operations. The default resolution for new images is 96 DPI.
image由图象创建函数(例如imagecreatetruecolor())返回的图象资源。
res_xThe horizontal resolution in DPI.
res_yThe vertical resolution in DPI.
When used as getter (that is without the optional parameters), it returns
TRUE on success, 或者在失败时返回 FALSE.
When used as setter (that is with one or both optional parameters given),
it returns an indexed array of the horizontal and vertical resolution on
success, 或者在失败时返回 FALSE.
Example #1 Setting and getting the resolution of an image
<?php
$im = imagecreatetruecolor(100, 100);
imageresolution($im, 200);
print_r(imageresolution($im));
imageresolution($im, 300, 72);
print_r(imageresolution($im));
?>
以上例程会输出：
Array
(
[0] => 200
[1] => 200
)
Array
(
[0] => 300
[1] => 72
)