GD: imagerotate produces inaccurate results #17982
Description
Description
The following code:
<?php
$gd = imagecreatetruecolor(5000,5000);
imagefill($gd, 0, 0, imagecolorallocate($gd, 255, 255, 255));
$rot = deg2rad(-1);
$a = cos($rot);
$b = sin($rot);
$gdAffine = imageaffine($gd, [$a ,$b, -$b, $a, 0, 0]);
ob_start();
imagejpeg($gdAffine);
$jpg = ob_get_clean();
echo '<img src="data:image/jpg;base64,'.base64_encode($jpg).'">';
$gdRotate = imagerotate($gd, rad2deg(-$rot), 0);
ob_start();
imagejpeg($gdRotate);
$jpg = ob_get_clean();
echo '<img src="data:image/jpg;base64,'.base64_encode($jpg).'">';Resulted in this output:
- This rotates a 5000x5000 canvas by 1 degree using both
imageaffineandimagerotate - This should result in a black triangle at the top of the canvas with a height of
5000*sin(1deg) = 87 pixels - Both methods produce a final canvas of
5087x5087which is the expected size imageaffineproduces a triangle of 87px high ✔imagerotateproduces a triangle of 73px high ❌ (this implies an actual rotation of ~0.83 degrees)- Looking to the right hand side of the top of
imagerotateshows substantial clipping, suggesting the image has been scaled up in some way and the edge pixels lost.
The image:
Top left of imageaffine followed by top left of imagerotate:
Top right of imageaffine showing pixels correctly go into edge
Top right of imagerotate showing substantial cropping of pixels along edge.
GD Version: 2.3.3
PHP Version
PHP 8.3.8
Operating System
No response