使用php gd库将彩色图像转换成黑白图像

Question

im having a page in which users upload their images to convert into black and white image..

i tried some of the code from internet but it works only for jpeg image when i upload some gif

or png images it shows an full black image or the same image with the same color scale...

any codes appreciated.

Answer 1

i cant tell because you didnt show us the code but it sounds like you need to test for the image type you got from the user before you init the image in GD.

i bet you have a problem with this function

$image = imagecreatefromjpeg ($filename);

you need to test for image type and optionally call one of these function

imagecreatefrompng ($filename)

imagecreatefromgif ($filename)

try this

if ($img = imagecreatefrompng($file))
else if ($img = imagecreatefromjpeg($file))

...

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Answer 2

Use the imagecolorallocatealpha() function to allocate color while keeping track of the background color.

Example:

 $color = imagecolorallocatealpha($image, 0, 0, 0,127); // transparent color