core-bundle/src/Resources/contao/library/Contao/GdImage.php
public function isSemitransparent()
	{
		if (!imageistruecolor($this->gdResource))
		{
			return false;
		}

		$width = imagesx($this->gdResource);
		$height = imagesy($this->gdResource);

		for ($x = 0; $x < $width; $x++)
		{
			for ($y = 0; $y < $height; $y++)
			{
				// Check if the pixel is semitransparent
				$alpha = (imagecolorat($this->gdResource, $x, $y) >> 24) & 0x7F;

				if ($alpha > 0 && $alpha < 127)
				{
					return true;
				}
			}
		}

		return false;
	}
public function isSemitransparent()
	{
		if (!imageistruecolor($this->gdResource))
		{
			return false;
		}

		$width = imagesx($this->gdResource);
		$height = imagesy($this->gdResource);

		for ($x = 0; $x < $width; $x++)
		{
			for ($y = 0; $y < $height; $y++)
			{
				// Check if the pixel is semitransparent
				$alpha = (imagecolorat($this->gdResource, $x, $y) >> 24) & 0x7F;

				if ($alpha > 0 && $alpha < 127)
				{
					return true;
				}
			}
		}

		return false;
	}
Detect if the image contains semitransparent pixels

@return boolean True if the image contains semitransparent pixels