在PHP中调整图像大小会创建黑色图像

Question

I wanted to resize an image in PHP using the GD library.

I found this question, which helped me alot. It allowed me to do exactly what I wanted. I changed the default value to true instead of the false in the answer, and I also added a way to resize png as well.

This resize_image function worked splendidly for all the images, until I wanted to scale down this image to 400x128 (landscape).

This created a black image. I even removed the parts I added on, and used the plain function copied from the question, and it still rendered black. This particular image seems to have trouble with other image sizes such as 400x400 as well. It all works as expected if you disable the crop option.

Is there something wrong with the math included in the function? I tried doing the math on paper replacing variables with the numbers I wanted, but I got confused midway.

PHPfiddle for an example. Try changing the values in the second last line to something else. It partially works (not to scale, even though cropping should be to scale).

Answer 1

When I debugged it, the width was negative. So, if I changed line 9 to the following

$width = abs(ceil($width-($width*abs($r-$w/$h))));

it's not black anymore. I don't check the formula whether it is correct or not as expected, but that abs() will make your image not black anymore.