imagealphablending

(PHP 4 >= 4.0.6, PHP 5, PHP 7, PHP 8)

imagealphablending — Set the blending mode for an image

Description

imagealphablending(GdImage $image, bool $enable): bool

imagealphablending() allows for two different modes of drawing on truecolor images. In blending mode, the alpha channel component of the color supplied to all drawing function, such as imagesetpixel() determines how much of the underlying color should be allowed to shine through. As a result, gd automatically blends the existing color at that point with the drawing color, and stores the result in the image. The resulting pixel is opaque. In non-blending mode, the drawing color is copied literally with its alpha channel information, replacing the destination pixel. Blending mode is not available when drawing on palette images.

Parameters

image: A GdImage object, returned by one of the image creation functions, such as imagecreatetruecolor().
enable: Whether to enable the blending mode or not. On true color images the default value is true otherwise the default value is false

Return Values

Returns true on success or false on failure.

Changelog

Version	Description
8.0.0	`image` expects a GdImage instance now; previously, a valid `gd` resource was expected.

Examples

Example #1 imagealphablending() usage example

<?php
// Create image
$im = imagecreatetruecolor(100, 100);

// Set alphablending to on
imagealphablending($im, true);

// Draw a square
imagefilledrectangle($im, 30, 30, 70, 70, imagecolorallocate($im, 255, 0, 0));

// Output
header('Content-Type: image/png');

imagepng($im);
imagedestroy($im);
?>

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User Contributed Notes 14 notes

down

barnabas at kendall dot NOSPAM dot net ¶

23 years ago

If you are trying to copy a transparant image on to another image, you might assume that you should apply the ImageAlphaBlending function to the image that has the transparancy, the source image. In reality, you must apply the ImageAlphaBlending function to the destination image. Basically it's saying, "make the specified image respect transparancy".



Here's a real world example. Suppose you want to put your logo on the upper left corner of a photograph. Your logo is a PNG with transparancy, and the photo is a JPEG. Here's what you would do:



<?php

$photoImage = ImageCreateFromJPEG('photo.jpg');

ImageAlphaBlending($photoImage, true);



$logoImage = ImageCreateFromPNG('logo.png');

$logoW = ImageSX($logoImage);

$logoH = ImageSY($logoImage);



ImageCopy($photoImage, $logoImage, 0, 0, 0, 0, $logoW, $logoH);



ImageJPEG($photoImage); // output to browser



ImageDestroy($photoImage);

ImageDestroy($logoImage);

?>

down

Jakub Argasi?ski ¶

19 years ago

I have been looking around for a while to find a script which does the following: generates image with text using specified font with given color, but with totally transparent background (by alpha-channnel, not via color transparency). Finally, I have created the script by myself. It's just a rough idea how to do it.

<?php
$tekst = "This is a test message\nza???? g??l? ja??!\nZA?ӣ? GʦL? JA???";

$h = 9;

$size = imageTTFBBox($h, 0, "arial.ttf", $tekst);
$image = imageCreateTrueColor(abs($size[2]) + abs($size[0]), abs($size[7]) + abs($size[1]));
imageSaveAlpha($image, true);
ImageAlphaBlending($image, false); 

$tlo = imagecolorallocatealpha($image, 220, 220, 220, 127);
imagefill($image, 0, 0, $tlo);

$napis = imagecolorallocate($image, 220, 220, 220);
imagettftext($image, $h, 0, 0, abs($size[5]), $napis, "arial.ttf", $tekst);
imagepng($image, "output.png");
imagedestroy($image);

?>
<html>
<head>
</head>
<body bgcolor="#808080">
<img src="output.png" alt="">
</body>
</html>

down

luke dot stanley at gmail dot com ¶

18 years ago

"If imagealphablending os set to true and you want to merge two images, you are left with no transparency. If it is set to false, only the transparency of the second image is respected, causing no parts of the first image to be shown. To solve this use the following function:"

dscharrer at gmail dot com offered this without a use example, so here is one:

<?

$flag = imagecreatefrompng('a.png');
$mask = imagecreatefrompng('b.png');

imagealphablending($flag, 1);
imagealphablending($mask, 1);
$i= array($flag, $mask); // here is the array of images, using the above specified $flag and $mask images

$s = imagemergealpha($i);

header("Content-type: image/png");
imagepng($s);

//Merge multiple images and keep transparency

//$i is and array of the images to be merged:
// $i[1] will be overlayed over $i[0]
// $i[2] will be overlayed over that
// ...

//the function returns the resulting image ready for saving

function imagemergealpha($i) {

 //create a new image
 $s = imagecreatetruecolor(imagesx($i[0]),imagesy($i[1]));
 
 //merge all images
 imagealphablending($s,true);
 $z = $i;
 while($d = each($z)) {
  imagecopy($s,$d[1],0,0,0,0,imagesx($d[1]),imagesy($d[1]));
 }
 
 //restore the transparency
 imagealphablending($s,false);
 $w = imagesx($s);
 $h = imagesy($s);
 for($x=0;$x<$w;$x++) {
  for($y=0;$y<$h;$y++) {
   $c = imagecolorat($s,$x,$y);
   $c = imagecolorsforindex($s,$c);
   $z = $i;
   $t = 0;
   while($d = each($z)) {
   $ta = imagecolorat($d[1],$x,$y);
   $ta = imagecolorsforindex($d[1],$ta);
   $t += 127-$ta['alpha'];
   }
   $t = ($t > 127) ? 127 : $t;
   $t = 127-$t;
   $c = imagecolorallocatealpha($s,$c['red'],$c['green'],$c['blue'],$t);
   imagesetpixel($s,$x,$y,$c);
  }
 }
 imagesavealpha($s,true);
 return $s;
}

?>

down

www.deebster.com ¶

21 years ago

Your target image resource not must be paletted if you want to use blending.

This means using ImageCreateTrueColor() rather than ImageCreate().

(If your source is e.g. a jpeg and you've used ImageCreateFromJPEG(), the above is irrelevant.)

down

jeppe dot dyrby at gmail dot com ¶

17 years ago

I have create a little function for putting a watermark on any picture.

Watermark can be png, with transparency, and the watermark can be placed anywhere on the image, using simple strings such as 'bottom-left', or 'center'.



<?

function imagelogo (&$dst_image, $src_image, $dst_w, $dst_h, $src_w, $src_h, $position='bottom-left') {

    imagealphablending($dst_image,true);

    imagealphablending($src_image,true);

    if ($position == 'random') {

        $position = rand(1,8);

    }

    switch ($position) {

        case 'top-right':

        case 'right-top':

        case 1:

            imagecopy($dst_image, $src_image, ($dst_w-$src_w), 0, 0, 0, $src_w, $src_h);

        break;

        case 'top-left':

        case 'left-top':

        case 2:

            imagecopy($dst_image, $src_image, 0, 0, 0, 0, $src_w, $src_h);

        break;

        case 'bottom-right':

        case 'right-bottom':

        case 3:

            imagecopy($dst_image, $src_image, ($dst_w-$src_w), ($dst_h-$src_h), 0, 0, $src_w, $src_h);

        break;

        case 'bottom-left':

        case 'left-bottom':

        case 4:

            imagecopy($dst_image, $src_image, 0 , ($dst_h-$src_h), 0, 0, $src_w, $src_h);

        break;

        case 'center':

        case 5:

            imagecopy($dst_image, $src_image, (($dst_w/2)-($src_w/2)), (($dst_h/2)-($src_h/2)), 0, 0, $src_w, $src_h);

        break;

        case 'top':

        case 6:

            imagecopy($dst_image, $src_image, (($dst_w/2)-($src_w/2)), 0, 0, 0, $src_w, $src_h);

        break;

        case 'bottom':

        case 7:

            imagecopy($dst_image, $src_image, (($dst_w/2)-($src_w/2)), ($dst_h-$src_h), 0, 0, $src_w, $src_h);

        break;

        case 'left':

        case 8:

            imagecopy($dst_image, $src_image, 0, (($dst_h/2)-($src_h/2)), 0, 0, $src_w, $src_h);

        break;

        case 'right':

        case 9:

            imagecopy($dst_image, $src_image, ($dst_w-$src_w), (($dst_h/2)-($src_h/2)), 0, 0, $src_w, $src_h);

        break;

    }

}



// example:



imagelogo($image, $watermark, imagesx($image), imagesy($image), imagesx($watermark), imagesy($watermark), 'random');

?>

down

JAYPEEsorenATgeeMail ¶

18 years ago

I rewrote the code given below to skip calculations and pixel setting when not needed (full opaque or full transparent pixels), as the content of my overlays is generally mostly transparent. Reduced processing time from ~0.17s to ~0.06s on 216x145px images.

function alphaOverlay($destImg, $overlayImg, $imgW, $imgH)
{
    for($y=0;$y<$imgH;$y++)
    {
        for($x=0;$x<$imgW;$x++)
        {
            $ovrARGB = imagecolorat($overlayImg, $x, $y);
            $ovrA = ($ovrARGB >> 24) << 1;
            $ovrR = $ovrARGB >> 16 & 0xFF;
            $ovrG = $ovrARGB >> 8 & 0xFF;
            $ovrB = $ovrARGB & 0xFF;
            
            $change = false;
            if($ovrA == 0)
            {
                $dstR = $ovrR;
                $dstG = $ovrG;
                $dstB = $ovrB;
                $change = true;
            }
            elseif($ovrA < 254)
            {
                $dstARGB = imagecolorat($destImg, $x, $y);
                $dstR = $dstARGB >> 16 & 0xFF;
                $dstG = $dstARGB >> 8 & 0xFF;
                $dstB = $dstARGB & 0xFF;
                
                $dstR = (($ovrR * (0xFF-$ovrA)) >> 8) + (($dstR * $ovrA) >> 8);
                $dstG = (($ovrG * (0xFF-$ovrA)) >> 8) + (($dstG * $ovrA) >> 8);
                $dstB = (($ovrB * (0xFF-$ovrA)) >> 8) + (($dstB * $ovrA) >> 8);
                $change = true;
            }
            if($change)
            {
                $dstRGB = imagecolorallocatealpha($destImg, $dstR, $dstG, $dstB, 0);
                imagesetpixel($destImg, $x, $y, $dstRGB);
            }
                
        }
    }
    return $destImg;
}

down

joe AT cerberon DOT net ¶

20 years ago

Note that alpha blending must be enabled to render antialiased text in true color mode.

For OLDER versions of PHP and/or GD (e.g. which comes with Debian woody) alpha blending is DISABLED by default and it is ENABLED for NEWER versions.

down

roONLYycoLOWERCAneSEjo at gmail dot com ¶

18 years ago

Roy Conejo says:

I' had to "per-pixel alpha blend" an image into a solid background, as seen on the very concise example from "barnabas at kendall dot NOSPAM dot net": an alpha blended .png logo on a .jpg photograph. The problem was... it doesn't worked out at all here (why? T_T).

Note that I'm using just the source alpha to determine how much colour from source and destination will be present on the final pixel... and that I've to multiply the alpha value (0 - 127) by 2 because I need it to be 8 bits for the calculations.

I think the code is pretty fast, no decimals, no rounding, no unnecesary coding. Bound checking or clipping could be implemented if you really need to.

I hope it helps someone on my same situation ^.^

<?php

    ## BEGIN of function alpha_blending -------------------------------------------
    function
    alpha_blending ($dest, $source, $dest_x, $dest_y) {
    
        ## lets blend source pixels with source alpha into destination =)
        for ($y = 0; $y < imagesy($source); $y++) {
            for ($x = 0; $x < imagesx($source); $x++) {
                            
                $argb_s = imagecolorat ($source    ,$x            ,$y);
                $argb_d = imagecolorat ($dest    ,$x+$dest_x    ,$y+$dest_y);
                            
                $a_s    = ($argb_s >> 24) << 1; ## 7 to 8 bits.
                $r_s    =  $argb_s >> 16     & 0xFF;
                $g_s    =  $argb_s >>  8    & 0xFF;
                $b_s    =  $argb_s            & 0xFF;
                                
                $r_d    =  $argb_d >> 16    & 0xFF;
                $g_d    =  $argb_d >>  8    & 0xFF;
                $b_d    =  $argb_d            & 0xFF;
                                
                ## source pixel 100% opaque (alpha == 0)
                if ($a_s == 0) { 
                    $r_d = $r_s; $g_d = $g_s; $b_d = $b_s;
                } 
                ## source pixel 100% transparent (alpha == 255)
                else if ($a_s > 253) {
                ## using source alpha only, we have to mix (100-"some") percent 
                ## of source with "some" percent of destination.
                } else {
                    $r_d = (($r_s * (0xFF-$a_s)) >> 8) + (($r_d * $a_s) >> 8);
                    $g_d = (($g_s * (0xFF-$a_s)) >> 8) + (($g_d * $a_s) >> 8);
                    $b_d = (($b_s * (0xFF-$a_s)) >> 8) + (($b_d * $a_s) >> 8);
                }
                                
                $rgb_d = imagecolorallocatealpha ($dest, $r_d, $g_d, $b_d, 0);
                imagesetpixel ($dest, $x, $y, $rgb_d);
            }
        }
    }
    ## END of function alpha_blending -------------------------------------------
    
    
    
    ## let's start loading images as usual...
    $source = imagecreatefrompng ('logo.png');
    $dest    = imagecreatefromjpg ('photo.jpg');

    ## alpha blend $source into $dest starting at 10, 5.
    alpha_blending ($dest, $source, 10, 5);    
    
    ## here you'll have to save "$dest" or send it to the browser...
    ## 
    
    imagedestroy ($source);
    imagedestroy ($dest);
    
?>

eof =p

down

boo at php dot net ¶

21 years ago

Notice that AlphaBlending is ON by default.
So, only use this function if you don't want to use AlphaBlending.

down

-2

klaproth at creative-mindworks dot de ¶

16 years ago

I have written a function that takes an image as parameter and returns the same image with a reflection effect (often seen in WEB 2.0 sites). I have not performance-tested this with large image files, for thumbnails it works fine (requires PHP 4.3.2 or above, or PHP5).

<?php
function imagereflection($src_img) {
  $src_height = imagesy($src_img);
  $src_width = imagesx($src_img);
  $dest_height = $src_height + ($src_height / 2);
  $dest_width = $src_width;
  
  $reflected = imagecreatetruecolor($dest_width, $dest_height);
  imagealphablending($reflected, false);
  imagesavealpha($reflected, true);
  
  imagecopy($reflected, $src_img, 0, 0, 0, 0, $src_width, $src_height);
  $reflection_height = $src_height / 2;
  $alpha_step = 80 / $reflection_height;
  for ($y = 1; $y <= $reflection_height; $y++) {
    for ($x = 0; $x < $dest_width; $x++) {
      // copy pixel from x / $src_height - y to x / $src_height + y
      $rgba = imagecolorat($src_img, $x, $src_height - $y);
      $alpha = ($rgba & 0x7F000000) >> 24;
      $alpha =  max($alpha, 47 + ($y * $alpha_step));
      $rgba = imagecolorsforindex($src_img, $rgba);
      $rgba = imagecolorallocatealpha($reflected, $rgba['red'], $rgba['green'], $rgba['blue'], $alpha);
      imagesetpixel($reflected, $x, $src_height + $y - 1, $rgba);
    }
  }
  
  return $reflected;
}
?>

This is rather hot-coded. You could go on and extract some of the values as parameters (80 is the transparency start value, $height / 2 is the reflection area...).

Cheers,
Christian

down

-1

Raisul Kabir Ruman ¶

18 years ago

In the previous message, I found it is working perfect. But, it can be done a lot easily, as is described by the first message by "barnabas at kendall dot NOSPAM dot net". Though, it don't work totally, instead of using imageAlphaBlending, you have to use imageSaveAlpha

So, I found the corrected and smalled code would be

<?php
$im_a = @imagecreatefrompng("a.png");
$im_c = @imagecreatefrompng("c.png");
imageSaveAlpha($im_c, true);

imagecopy($im_c,$im_a,0,0,0,0,200,200);
header("Content-type: image/png");
imagepng($im_c);
?>

down

-1

dscharrer at gmail dot com ¶

19 years ago

If imagealphablending os set to true and you want to merge two images, you are left with no transparency. If it is set to false, only the transparency of the second image is respected, causing no parts of the first image to be shown. To solve this use the following function:

<?
//Merge multiple images and keep transparency

//$i is and array of the images to be merged:
// $i[1] will be overlayed over $i[0]
// $i[2] will be overlayed over that
// ...

//the function returns the resulting image ready for saving

function imagemergealpha($i) {

 //create a new image
 $s = imagecreatetruecolor(imagesx($i[0]),imagesy($i[1]));
 
 //merge all images
 imagealphablending($s,true);
 $z = $i;
 while($d = each($z)) {
  imagecopy($s,$d[1],0,0,0,0,imagesx($d[1]),imagesy($d[1]));
 }
 
 //restore the transparency
 imagealphablending($s,false);
 $w = imagesx($s);
 $h = imagesy($s);
 for($x=0;$x<$w;$x++) {
  for($y=0;$y<$h;$y++) {
   $c = imagecolorat($s,$x,$y);
   $c = imagecolorsforindex($s,$c);
   $z = $i;
   $t = 0;
   while($d = each($z)) {
    $ta = imagecolorat($d[1],$x,$y);
    $ta = imagecolorsforindex($d[1],$ta);
    $t += 127-$ta['alpha'];
   }
   $t = ($t > 127) ? 127 : $t;
   $t = 127-$t;
   $c = imagecolorallocatealpha($s,$c['red'],$c['green'],$c['blue'],$t);
   imagesetpixel($s,$x,$y,$c);
  }
 }
 imagesavealpha($s,true);
 return $s;
}
?>

down

-2

webmaster at nweurosport dot com ¶

19 years ago

When saving images for use in transparent overlays like the logo addition mentioned above I've found that it is not succesful with PNG-24, only GIF and PNG-8.  I've had great success with PNG-8's.

down

-4

tcarter at roundcorners dot com ¶

22 years ago

If you are saving an image as PNG with transparency then saving it as a PNG-8 will give it transparency in the same way GIF has, but that won't work with this function. 

For this function to work the image needs to have an alpha channel (obviously really when you think about it), so make sure you save as PNG-24

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