在另一个图像中隐藏图像php gd

Question

我想在另一个图像（png）中隐藏/加密图像（png）并在PHP GD中获取加密图像。我试图添加每个RGB像素值并获取新图像。但是它仍然无法隐藏原始图像。

<?php

ini_set('memory_limit','-1');
header("Content-type: image/png");

$im     = imagecreatefrompng("sar.png");
$cipher = imagecreatefrompng("sar_cipher.png");

for($x = 0 ; $x<1024; $x++){
    for($y =0; $y<768; $y++){

        $rgb = imagecolorat($im, $x, $y);
        $r   = ($rgb >> 16) & 0xFF;
        $g   = ($rgb >> 8) & 0xFF;
        $b   = $rgb & 0xFF;

        $ciRgb = imagecolorat($cipher, $x, $y);
        $Cr    = ($ciRgb >> 16) & 0xFF;
        $Cg    = ($ciRgb >> 8) & 0xFF;
        $Cb    = $ciRgb & 0xFF;

        $newRed   = $r+$Cr;
        $newGreen = $g+$Cg;
        $newBlue  = $b+$Cb;

        if($newRed > 255 ) {
            //echo "Red is ".$newRed;
            $newRed = $newRed - 255;
        }

        if($newGreen > 255 )
            $newGreen = $newGreen - 255;

        if($newBlue > 255 )
            $newBlue = $newBlue - 255;

        // initialize new color
        $newColor = $a | $newRed  << 16 | $newGreen << 8 |$newBlue ;

        // set color at x , y on image
        imagesetpixel($im, $x, $y, $newColor);

    }

}

imagepng($im,"encrypted_image.png");
imagepng($im);
imagedestroy($im);

?>

如何将原始图像完全隐藏在另一个图像中？