How to set the alpha blending flag to use layering effects using imaglayereffect() function in PHP?

The imagelayereffect() function is an inbuilt PHP function used to set alpha blending flags for layering effects on images. It controls how pixels are blended when drawing on an image, returning true on success or false on failure.

Syntax

bool imagelayereffect($image, $effect)

Parameters

The function accepts two parameters ?

• $image − An image resource created by image creation functions like imagecreatetruecolor().

• $effect − The blending effect constant to apply. Available constants are ?

  • IMG_EFFECT_REPLACE − Sets pixel replacement mode (similar to imagealphablending($image, true))

  • IMG_EFFECT_ALPHABLEND − Sets normal pixel blending (equivalent to imagealphablending($image, false))

  • IMG_EFFECT_NORMAL − Same as IMG_EFFECT_ALPHABLEND

  • IMG_EFFECT_OVERLAY − White pixels remain white, black pixels remain black, grey pixels take foreground color

  • IMG_EFFECT_MULTIPLY − Applies multiply blending effect

Return Value

Returns true on success or false on failure.

Example − Using IMG_EFFECT_OVERLAY

This example demonstrates the overlay effect with colored ellipses ?

<?php
   // Create an image
   $img = imagecreatetruecolor(700, 300);
   
   // Set grey background
   imagefilledrectangle($img, 0, 0, 150, 150, imagecolorallocate($img, 122, 122, 122));

   // Apply overlay blending effect
   imagelayereffect($img, IMG_EFFECT_OVERLAY);

   // Draw colored ellipses
   imagefilledellipse($img, 50, 50, 40, 40, imagecolorallocate($img, 100, 255, 100));
   imagefilledellipse($img, 50, 50, 50, 80, imagecolorallocate($img, 100, 100, 255));
   imagefilledellipse($img, 50, 50, 80, 50, imagecolorallocate($img, 255, 0, 0));

   // Output image
   header('Content-type: image/png');
   imagepng($img);
   imagedestroy($img);
?>

Example − Using IMG_EFFECT_REPLACE

This example shows pixel replacement mode with concentric circles ?

<?php
   // Create an image
   $img = imagecreatetruecolor(700, 200);

   // Set grey background
   imagefilledrectangle($img, 0, 0, 200, 200, imagecolorallocate($img, 122, 122, 122));

   // Apply replace blending effect
   imagelayereffect($img, IMG_EFFECT_REPLACE);

   // Draw concentric circles
   imagefilledellipse($img, 100, 100, 160, 160, imagecolorallocate($img, 0, 0, 0));
   imagefilledellipse($img, 100, 100, 140, 140, imagecolorallocate($img, 0, 0, 255));
   imagefilledellipse($img, 100, 100, 100, 100, imagecolorallocate($img, 255, 0, 0));

   // Output image
   header('Content-type: image/png');
   imagepng($img);
   imagedestroy($img);
?>

Note: These examples require the GD extension and output images directly to the browser. To save images to files, use imagepng($img, 'filename.png') instead.

Conclusion

The imagelayereffect() function provides powerful control over pixel blending in PHP image manipulation. Use IMG_EFFECT_OVERLAY for artistic effects and IMG_EFFECT_REPLACE for standard layering without transparency blending.