<?php$im = imagecreate(255, 255);$bg = imagecolorallocate($im, 0, 0, 0);for ($i = 255; $i >= 0; $i--) {$color = imagecolorallocate($im, $i, $i, $i);imagefilledrectangle($im, 0, $i, 255, 1, $color);}header("Content-type: image/png");imagepng($im);imagedestroy($im);?>效果图如下: