imagecolorallocatealpha - PHP code example

The php Function Imagecolorallocatealpha

The php function imagecolorallocatealpha is an inbuilt PHP function that allocates the color for an image. It accepts five parameters and returns the identifier of the new color on successful execution of the program. The alpha parameter of the image can be between 0 and 127 where 0 represents completely opaque while 127 indicates fully transparent.

The function must be called for each individual color that is to be used in a palette-based image. It can also be used to fill the background color in true-color images that are created from imagecreatetruecolor. It is also the first function to be called when converting a true-color image to a pallette image for PNG-8 compression.

Functions in PHP have a clear "define-and-call" pattern: they are defined by describing what they do, then they are called when it is time to do them. To call a function, you simply reference the function name and pass in any arguments that are required by the function. Arguments are data that you want to send to the function and can be passed in as either a string or an array. You must include them in parenthesis, and you can add as many arguments as you want.

The imagecolorallocatealpha function is part of the GD Library which is a collection of functions for working with images and other graphics types. This is the most common library that is included with most PHP installations and allows you to create, edit and manipulate images and other graphics files.

imagecolorallocatealpha example

// Validate or set background color argument.     if (!empty($arguments['background'])) {
      // Validate the background color: Color::hexToRgb does so for us.       $background = Color::hexToRgb($arguments['background']) + ['alpha' => 0];
    }
    else {
      // Background color is not specified: use transparent white as background.       $background = ['red' => 255, 'green' => 255, 'blue' => 255, 'alpha' => 127];
    }
    // Store the color index for the background as that is what GD uses.     $arguments['background_idx'] = imagecolorallocatealpha($this->getToolkit()->getResource(), $background['red'], $background['green'], $background['blue'], $background['alpha']);

    if ($this->getToolkit()->getType() === IMAGETYPE_GIF) {
      // GIF does not work with a transparency channel, but can define 1 color       // in its palette to act as transparent.
      // Get the current transparent color, if any.       $gif_transparent_id = imagecolortransparent($this->getToolkit()->getResource());
      if ($gif_transparent_id !== -1) {
        // The gif already has a transparent color set: remember it to set it on         // the rotated image as well.         $arguments['gif_transparent_color'] = imagecolorsforindex($this->getToolkit()->getResource(), $gif_transparent_id);

// Create the resource.     if (!$res = imagecreatetruecolor($arguments['width'], $arguments['height'])) {
      return FALSE;
    }

    // Fill the resource with transparency as possible.     switch ($type) {
      case IMAGETYPE_PNG:
      case IMAGETYPE_WEBP:
        imagealphablending($res, FALSE);
        $transparency = imagecolorallocatealpha($res, 0, 0, 0, 127);
        imagefill($res, 0, 0, $transparency);
        imagealphablending($res, TRUE);
        imagesavealpha($res, TRUE);
        break;

      case IMAGETYPE_GIF:
        if (empty($arguments['transparent_color'])) {
          // No transparency color specified, fill white transparent.           $fill_color = imagecolorallocatealpha($res, 255, 255, 255, 127);
        }
        else {

/** * Rotates current image counter-clockwise by $angle. * Ported from image-edit.php * * @since 3.5.0 * * @param float $angle * @return true|WP_Error */
    public function rotate( $angle ) {
        if ( function_exists( 'imagerotate' ) ) {
            $transparency = imagecolorallocatealpha( $this->image, 255, 255, 255, 127 );
            $rotated      = imagerotate( $this->image, $angle, $transparency );

            if ( is_gd_image( $rotated ) ) {
                imagealphablending( $rotated, true );
                imagesavealpha( $rotated, true );
                imagedestroy( $this->image );
                $this->image = $rotated;
                $this->update_size();
                return true;
            }
        }