Mike42\Escpos\EscposImage::toRasterFormat PHP Method

    public function toRasterFormat()
    {
        // Just wraps implementations for caching & lazy loading
        if ($this->imgRasterData !== null) {
            /* Return cached value */
            return $this->imgRasterData;
        }
        if ($this->allowOptimisations) {
            /* Use optimised code if allowed */
            $this->imgRasterData = $this->getRasterFormatFromFile($this->filename);
        }
        if ($this->imgRasterData === null) {
            /* Load in full image and render the slow way if no faster implementation
               is available, or if we've been asked not to use it */
            if ($this->imgData === null) {
                $this->loadImageData($this->filename);
            }
            $this->imgRasterData = $this->getRasterFormat();
        }
        return $this->imgRasterData;
    }

 /**
  * Print an image to the printer.
  * 
  * Size modifiers are:
  * - IMG_DEFAULT (leave image at original size)
  * - IMG_DOUBLE_WIDTH
  * - IMG_DOUBLE_HEIGHT
  * 
  * See the example/ folder for detailed examples.
  * 
  * The function bitImage() takes the same parameters, and can be used if
  * your printer doesn't support the newer graphics commands.
  * 
  * @param EscposImage $img The image to print.
  * @param int $size Output size modifier for the image.
  */
 function graphics(EscposImage $img, $size = self::IMG_DEFAULT)
 {
     self::validateInteger($size, 0, 3, __FUNCTION__);
     $imgHeader = self::dataHeader(array($img->getWidth(), $img->getHeight()), true);
     $tone = '0';
     $colors = '1';
     $xm = ($size & self::IMG_DOUBLE_WIDTH) == self::IMG_DOUBLE_WIDTH ? chr(2) : chr(1);
     $ym = ($size & self::IMG_DOUBLE_HEIGHT) == self::IMG_DOUBLE_HEIGHT ? chr(2) : chr(1);
     $header = $tone . $xm . $ym . $colors . $imgHeader;
     $this->wrapperSendGraphicsData('0', 'p', $header . $img->toRasterFormat());
     $this->wrapperSendGraphicsData('0', '2');
 }