Drawing on image with the GD library in PHP

问题

I have created a code to generate a random pattern image. it creates an image with given width and height and fills it with small 40x40 pixel rectangles. this is my code:

<?php 

$width = 1000; 
$height = 600;

$image_p = imagecreate($width, $height); 
$baseR = 255 - rand(0, 100);
$baseG = 255 - rand(0, 100);
$baseB = 255 - rand(0, 100);

for ($i = 0; $i <= floor($width / 40); $i++){
for ($j = 0; $j <= floor($height / 40); $j++){
  $val = floor(100 * (rand(0, 100) / 100));
  $r = $baseR - $val;
  $g = $baseG - $val;
  $b = $baseB - $val;
  $color = imagecolorallocate($image_p, $r, $g, $b); 
  imagefilledrectangle($image_p, $i * 40, $j * 40, (($i + 1) * 40), (($j + 1) * 40), $color);

}
}

imagejpeg($image_p, 'my_dir/test.jpg'); 

?>

there's no problem when i set the width to a value like 640 and the height to 400. but if i set the width to 1000 and the height to 800, there will be a blank area on the right side of the image which is not covered by rectangles. I implemented the same code in delphi and it worked perfectly, but in PHP...!

回答1:

Change imagecreate to imagecreatetruecolor

You're creating a palette based image with 255 colors max. You're running out of colors to allocate at the end and it's recycling the last color on the palette for the remainder of the blocks.

来源：https://stackoverflow.com/questions/24395843/drawing-on-image-with-the-gd-library-in-php