PHP GD library instance 4= Turn the image to black and white

This technique, we know the basic practice of GD library, uses fewer scenarios, but if you can do it, it will always make you stand out in more situations; Lay the foundation for our technology

/ / black and white
$image_path = "1.jpg";
// $image_path="2.png";
$im = imagecreatefromjpeg($image_path);
// ImagecreateFromgIf for Gif, imagecreatefrompng for PNG...
if (imageistruecolor($im)) {
    imagetruecolortopalette($im.false.256);
    // If it is a true color image, convert the true color image to a palette image
}
for ($i = 0; $i < imagecolorstotal($im);/* Get the number of colors in the palette */ $i{+ +)$rgb = imagecolorsforindex($im.$i);// Get the color value of the color I point
    $gray = round(0.229 * $rgb['red'] + 0.587 * $rgb['green'] + 0.114 * $rgb['blue']);
    // Get the gray value of the color
    if ($gray< =128) $gray = 0; else $gray = 255;
    imagecolorset($im.$i.$gray.$gray.$gray);// Set the I point color value
}
header('Content-Type: image/jpeg');
// Set the image type. Also, if you want to generate a GIF or PNG image, replace it with the corresponding header
imagejpeg($im);
// Use imagegIf for GIF and imagepng for PNG.
imagedestroy($im);
// Destroy images to release resources
 

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