GD and Image 函数
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imagecolortransparent

(PHP 4, PHP 5)

imagecolortransparent — 将某个颜色定义为透明色

说明

int imagecolortransparent ( resource $image [, int $color ] )

imagecolortransparent() 将 image 图像中的透明色设定为 color。image 是 imagecreatetruecolor() 返回的图像标识符，color 是 imagecolorallocate() 返回的颜色标识符。

Note:

透明色是图像的一种属性，透明度不是颜色的属性。一旦设定了某个颜色为透明色，图像中之前画为该色的任何区域都成为透明的。

返回新透明色的标识符，如果省略 color 则返回当前透明色的标识符。

Note:

透明度仅能通过 imagecopymerge() 和真彩色图像拷贝，不能用 imagecopy() 或调色板图像。

GD and Image 函数
在线手册：中文 英文
PHP手册
PHP手册 - N: 将某个颜色定义为透明色

用户评论:

Jalpa Bhavsar (07-Mar-2012 02:27)

Thanks john, this really help me.

While creating a Text Image by setting a color  - "Image shows black background marks behind the TEXT ". After using your method,
 It gave me a proper Image with Proper Color.

/*********************************************/
A transparent background with text doesn't seem to work very well because of the antialiasing . But I tried the following kluge and it turned out very well:

   $im = imagecreatetruecolor(100,20);
   $almostblack = imagecolorallocate($im,254,254,254);
   imagefill($im,0,0,$almostblack);
   $black = imagecolorallocate($im,0,0,0);
   imagecolortransparent($im,$almostblack);
   ... set x and y..
   imagettftext($im,8,0,$x,$y,$black,"calibri.ttf",$txt);
/*********************************************/

john at jbwalker dot com (24-Jan-2012 04:42)

A transparent background with text doesn't seem to work very well because of the antialiasing . But I tried the following kluge and it turned out very well:

   $im = imagecreatetruecolor(100,20);
   $almostblack = imagecolorallocate($im,254,254,254);
   imagefill($im,0,0,$almostblack);
   $black = imagecolorallocate($im,0,0,0);
   imagecolortransparent($im,$almostblack);
   ... set x and y..
   imagettftext($im,8,0,$x,$y,$black,"calibri.ttf",$txt);

email at vladislav dot net (22-Jun-2011 10:42)

Pay attention, that some GIF images may not include a transparent color. A good example of forced transparency in resized GIF image was given by markglibres at yahoo dot com 29-Mar-2009 02:48. But sometimes the transparent color in GIF images can be not set. The problem is, that the color you force to be transparent can be used in the original GIF as opaque and you will loose that color in resized image. The solution is not to use some default transparent color and to leave the resized image without transparent color (the same as original GIF). I used (nearly) the following code to make resized GIF images trnsparent  only when the transparency is needed:

<?php
/* ... */

$img = ImageCreateFromGIF($f); /* create image from existing GIF: original image file name $f you may take from where you need */
$transparent_index = ImageColorTransparent($img); /* gives the index of current transparent color or -1 */
if($transparent_index!=(-1)) $transparent_color = ImageColorsForIndex($img,$transparent_index);

/* ... */

$img_resized = ImageCreateTrueColor( $nw, $nh ); /* (the new width $nw and height $nh must be defined before) */
if(!empty($transparent_color)) /* simple check to find wether transparent color was set or not */
{
    $transparent_new = ImageColorAllocate( $img_resized, $transparent_color['red'], $transparent_color['green'], $transparent_color['blue'] );
    $transparent_new_index = ImageColorTransparent( $img_resized, $transparent_new );
    ImageFill( $img_resized, 0,0, $transparent_new_index ); /* don't forget to fill the new image with the transparent color */
}
list($w,$h) = GetImageSize($f); /* defines the original width $w and height $h */
if( ImageCopyResized( $img_resized, $img, 0,0, 0,0, $nw,$nh, $w,$h ) ) /* resized copying and replacing the original image */
{
    ImageDestroy($img);
    $img = $img_resized;
}

/* ... */

header('Content-Type: image/gif');
ImageGIF($img);
ImageDestroy($img);
?>

P.S.
If there some errors, I hope you could understood the idea.

admin at fastproxyservers dot org (30-Sep-2010 05:00)

I would like to share with others how to make PNG image transparent. I have tried almost all examples described on that page but none of them work for me. Finally I found the solution, but there is a bit cheating :) but who cares if it works?

So when I tried to allocate white (as an example) color as a transparent, it worked randomly (lets say 1 in 10 examples). That in turn pushed me to the idea that the problem is that white color is already exist in color palette. So if I try to add another white color with DIFFERENT index as a transparent, that will cause error.

So I found the solution, instead of adding new index, I searched for the white color’s index in the color palette and made it defined as transparent :) The best idea is to use not a white but left bottom corner as transparent color (I guess that s standard for some other software languages).

<?php
$index = imagecolorexact($this->image, 255, 255, 255);
imagecolortransparent($this->image, $index);
?>

All you need is to add that two lines before outputting your result.

ajamal (22-May-2009 02:06)

This might be of importance to newbies...If you are trying to create GIF's with transparencies, stick to the 216 colour pallet for all colours on the image... or transparencies wont work...at the very least yo will get dithering...

markglibres at yahoo dot com (29-Mar-2009 02:48)

I've made a very simple script that will retain transparency of images especially when resizing.

NOTE: Transparency is only supported on GIF and PNG files.

Parameters:

$new_image = image resource identifier such as returned by imagecreatetruecolor(). must be passed by reference
$image_source = image resource identifier returned by imagecreatefromjpeg, imagecreatefromgif and imagecreatefrompng. must be passed by reference

<?php
function setTransparency($new_image,$image_source)
    {
       
            $transparencyIndex = imagecolortransparent($image_source);
            $transparencyColor = array('red' => 255, 'green' => 255, 'blue' => 255);
            
            if ($transparencyIndex >= 0) {
                $transparencyColor    = imagecolorsforindex($image_source, $transparencyIndex);   
            }
           
            $transparencyIndex    = imagecolorallocate($new_image, $transparencyColor['red'], $transparencyColor['green'], $transparencyColor['blue']);
            imagefill($new_image, 0, 0, $transparencyIndex);
             imagecolortransparent($new_image, $transparencyIndex);
       
    }
?>


Sample Usage: (resizing)

<?php
$image_source = imagecreatefrompng('test.png');
$new_image = imagecreatetruecolor($width, $height);
setTransparency($new_image,$image_source);
imagecopyresampled($new_image, $image_source, 0, 0, 0, 0, $new_width, $new_height, $old_width, $old_height);
?>

designovermatter at gmail dot com (14-Jan-2009 12:03)

I was searching for a PHP code that makes transparent rounded corners and found none. So had to write my own:

<?php

$image = "v.png";
$corner = 40;

file_exists($image) or die("No such file: ".$image); //check if image exists before processing

$dim = getimagesize($image);

//create from type handle
if($dim[2] == 1) $new = imagecreatefromjpeg($image);
elseif($dim[2] == 2) $new = imagecreatefromgif($image);
elseif($dim[2] == 3) $new = imagecreatefrompng($image);
else die("Unsupported format: ".$dim[2]);

//find colorcode
$palette = imagecreatetruecolor($dim[0], $dim[1]);
$found = false;
while($found == false) {
   
    $r = rand(0, 255);
    $g = rand(0, 255);
    $b = rand(0, 255);
   
    if(imagecolorexact($new, $r, $g, $b) != (-1)) {
       
        $colorcode = imagecolorallocate($palette, $r, $g, $b);
        $found = true;
           
    }
   
}

//draw corners
imagearc($new, $corner-1, $corner-1, $corner*2, $corner*2, 180, 270, $colorcode);
imagefilltoborder($new, 0, 0, $colorcode, $colorcode);

imagearc($new, $dim[0]-$corner, $corner-1, $corner*2, $corner*2, 270, 0, $colorcode);
imagefilltoborder($new, $dim[0], 0, $colorcode, $colorcode);

imagearc($new, $corner-1, $dim[1]-$corner, $corner*2, $corner*2, 90, 180, $colorcode);
imagefilltoborder($new, 0, $dim[1], $colorcode, $colorcode);

imagearc($new, $dim[0]-$corner, $dim[1]-$corner, $corner*2, $corner*2, 0, 90, $colorcode);
imagefilltoborder($new, $dim[1], $dim[1], $colorcode, $colorcode);

imagecolortransparent($new, $colorcode); //make corners transparent

//display rounded image
header("Content: image/png");
imagepng($new);
imagedestroy($new);

?>

It draws an arc and fills to border with a colorcode - a color that doesnot exist in current image, to make it transparent in the end.

steved at HaHaHa dot com dot au (25-Oct-2008 06:28)

How to center your text both vertically and horizontally in a GD image:

<?php
//get box size
$box = imagettfbbox($titlesize, 0, $titlefont, $title);
       
//Find out the width and height of the text box
$textW = $box[2] - $box[0];
$textH = $box[5] - $box[3];
       
// Calculate the positions
$positionLeft = ($width - $textW)/2;
$positionTop = (($height - $textH)/2);
       
// Add some text
if($align=="center"){   
imagettftext($pic, size, angle, $positionLeft, $positionTop, colour, font, message);
?>

cca220v (11-Sep-2008 10:47)

I found out the hard way that for two png's with alpha transparency to correctly stack you need to explicitly re-enable alpha blending.

$img=imagecreatetruecolor($dx,$dy);
$img1=imagecreatefrompng($png1); //first layer
$img2=imagecreatefrompng($png2); //second layer (smaller image)

imagealphablending($img, false);
$transparent = imagecolorallocatealpha($img, 0, 0, 0, 127);
imagefill($img, 0, 0, $transparent);
imagesavealpha($img,true);
imagealphablending($img, true); //removing this causes the second layer's transparency to go trough the 1st layer erasing it (the image >is< transparent there ... as is the 2nd layer ... but not the 1st so it should not be transparent)

imagecopyresampled($img,$img1,
imagecopyresampled($img,$img2,

yousuf at philipz dot com (01-Apr-2008 07:45)

Well 8-bit gif and png files can have multiple transparent colors, so detecting the transparent color by manually looking into the file or using imagecolortransparent and using the detected rgb color as the background color when imagecopy'ing (or other image copying functions) on a true color image will not work. The only means of getting the transparent pixels to appear is to copy the pixel colors one by one to a new true color image. Here's some code i wrote to do this.

$original_image = @imagecreatefromgif( $original_image_file );

$original_image_width = imagesx( $original_image );
$original_image_height = imagesy( $original_image );

if ( !imageistruecolor($original_image) ) {
   # detects if its non-true color image
   if ( imagecolortransparent($original_image) >= 0 ) {
      # detects if any of the color palette has been set to transparent
      $truecolor = imagecreatetruecolor( $original_image_width, $original_image_height );
      for ($x = 0; $x < $original_image_width; $x++) {
         for ($y = 0; $y < $original_image_height; $y++) {
            $color_index = ImageColorAt($original_image, $x, $y);
            if ( !$color_palette[$color_index] ) {
               $rgb = imagecolorsforindex($original_image, $color_index);
               $color_to_set = imagecolorallocate($truecolor, $rgb['red'], $rgb['green'], $rgb['blue']);
               $color_palette[$color_index] = $color_to_set;
            } else {
               $color_to_set = $color_palette[$color_index];
            }
            imagesetpixel($truecolor, $x, $y, $color_to_set);
         }
      }
      imagedestroy($original_image);
      $original_image = $truecolor;
   }
}

kroccamen, gmail (27-Mar-2008 01:56)

Sorry, below should be:

<?php
$is_alpha = ord (file_get_contents ($file_path, false, null, 25, 1)) & 4;
?>

much better :)
Both types 4 (greyscale transparent png), and 6 (colour transparent png) have bit 4 set, so there's no need to bitwise twice and there's no need for == as the return value will be 4 or 0, which is easily interpreted as true or false elsewhere in your code.

note: file_get_contents isn't reading the whole file in this instance, just 1 byte on its own and that's it, so you can be assured this is fast and safe.

kroccamen, gmail (25-Mar-2008 12:44)

@wesley gunn:
Thank you very, very much for the code to determine if a PNG is 24 or 32-bit :)
Here's an improved version in one line without using a file-handle

<?php
$is_alpha = ((ord (
    file_get_contents ($filename, false, null, 25, 1)
) & 6) & 4) == 4;
?>

Gives true for a PNG with alpha, false otherwise.
This cannot detect 8-bit PNGs with transparency, but you could do that by searching the file contents for the presence of "PLTE" *AND* "tRNS".

tomas at cimax dot com (10-Mar-2008 08:19)

On some versions you must set the index number of that color in color pallete rather than the color! So if you allocate color with imagecolorallocate, that this color gets 0 index on color pallete so than you must call: imagecolortransparent ( resource $image , 0 ) to make the image transparent!

Anonymous (28-Feb-2008 10:52)

I came across some images that have transparent color allocated even if they don't have any transparent pixels (transparent color is unused).

fmkaiba at optonline dot net (07-Feb-2008 04:05)

This is my 'perfect' (i use that word lightly) thumbnail generation script, switch '$transparency' to true to have it do its best to handle transparency in gifs and pngs. this code is built off of comments and advice of everyone else here, and i do not deserve full credit. So far this handles every error i can throw at it.
<?php
function createthumb($name, $newname, $new_w, $new_h, $border=false, $transparency=true, $base64=false) {
    if(file_exists($newname))
        @unlink($newname);
    if(!file_exists($name))
        return false;
    $arr = split("\.",$name);
    $ext = $arr[count($arr)-1];

    if($ext=="jpeg" || $ext=="jpg"){
        $img = @imagecreatefromjpeg($name);
    } elseif($ext=="png"){
        $img = @imagecreatefrompng($name);
    } elseif($ext=="gif") {
        $img = @imagecreatefromgif($name);
    }
    if(!$img)
        return false;
    $old_x = imageSX($img);
    $old_y = imageSY($img);
    if($old_x < $new_w && $old_y < $new_h) {
        $thumb_w = $old_x;
        $thumb_h = $old_y;
    } elseif ($old_x > $old_y) {
        $thumb_w = $new_w;
        $thumb_h = floor(($old_y*($new_h/$old_x)));
    } elseif ($old_x < $old_y) {
        $thumb_w = floor($old_x*($new_w/$old_y));
        $thumb_h = $new_h;
    } elseif ($old_x == $old_y) {
        $thumb_w = $new_w;
        $thumb_h = $new_h;
    }
    $thumb_w = ($thumb_w<1) ? 1 : $thumb_w;
    $thumb_h = ($thumb_h<1) ? 1 : $thumb_h;
    $new_img = ImageCreateTrueColor($thumb_w, $thumb_h);
   
    if($transparency) {
        if($ext=="png") {
            imagealphablending($new_img, false);
            $colorTransparent = imagecolorallocatealpha($new_img, 0, 0, 0, 127);
            imagefill($new_img, 0, 0, $colorTransparent);
            imagesavealpha($new_img, true);
        } elseif($ext=="gif") {
            $trnprt_indx = imagecolortransparent($img);
            if ($trnprt_indx >= 0) {
                //its transparent
                $trnprt_color = imagecolorsforindex($img, $trnprt_indx);
                $trnprt_indx = imagecolorallocate($new_img, $trnprt_color['red'], $trnprt_color['green'], $trnprt_color['blue']);
                imagefill($new_img, 0, 0, $trnprt_indx);
                imagecolortransparent($new_img, $trnprt_indx);
            }
        }
    } else {
        Imagefill($new_img, 0, 0, imagecolorallocate($new_img, 255, 255, 255));
    }
   
    imagecopyresampled($new_img, $img, 0,0,0,0, $thumb_w, $thumb_h, $old_x, $old_y);
    if($border) {
        $black = imagecolorallocate($new_img, 0, 0, 0);
        imagerectangle($new_img,0,0, $thumb_w, $thumb_h, $black);
    }
    if($base64) {
        ob_start();
        imagepng($new_img);
        $img = ob_get_contents();
        ob_end_clean();
        $return = base64_encode($img);
    } else {
        if($ext=="jpeg" || $ext=="jpg"){
            imagejpeg($new_img, $newname);
            $return = true;
        } elseif($ext=="png"){
            imagepng($new_img, $newname);
            $return = true;
        } elseif($ext=="gif") {
            imagegif($new_img, $newname);
            $return = true;
        }
    }
    imagedestroy($new_img);
    imagedestroy($img);
    return $return;
}
//example useage
createthumb("img.gif", "tn_img.gif", 64,64,true, true, false);
?>

wesley dot gunn at email dot it (13-Nov-2007 05:27)

a simple way to check png with alpha channel reading IHDR PNG HEADER

$readPng =    fopen    ($argSourceImagePath, "rb");
$readAlp =    fread    ($readPng, 52);
            fclose    ($readPng);

if(substr(bin2hex($readAlp),50,2) == "04" || substr(bin2hex($readAlp),50,2) == "06")
echo("Png has alpha");

Rob (09-Oct-2007 03:55)

This block of code should preserve transparency when resizing an image using the GD library.

<?php
/**
 * Try to preserve transparency info
 * $orig_type - Original Image Type
 * $orig_img  - GD Image Resource for original image
 * $new_img   - GD Image Resource for resized image
 */

// Transparency only available for GIFs & PNGs
if ( ($orig_type == IMAGETYPE_GIF) || ($orig_type == IMAGETYPE_PNG) ) {
    $trnprt_indx = imagecolortransparent($orig_img);

    // If we have a specific transparent color
    if ($trnprt_indx >= 0) {

        // Get the original image's transparent color's RGB values
        $trnprt_color    = imagecolorsforindex($orig_img, $trnprt_indx);

        // Allocate the same color in the new image resource
        $trnprt_indx    = imagecolorallocate($new_img, $trnprt_color['red'], $trnprt_color['green'], $trnprt_color['blue']);

        // Completely fill the background of the new image with allocated color.
        imagefill($new_img, 0, 0, $trnprt_indx);

        // Set the background color for new image to transparent
        imagecolortransparent($new_img, $trnprt_indx);

    // Always make a transparent background color for PNGs that don't have one allocated already
    } elseif ($orig_type == IMAGETYPE_PNG) {

        // Turn off transparency blending (temporarily)
        imagealphablending($new_img, false);

        // Create a new transparent color for image
        $color = imagecolorallocatealpha($new_img, 0, 0, 0, 127);

        // Completely fill the background of the new image with allocated color.
        imagefill($this->new_img, 0, 0, $color);

        // Restore transparency blending
        imagesavealpha($this->new_img, true);
    }
}
?>

kevinoe at gmail (11-Sep-2007 09:39)

To resize a transparent image into a thumbnail while keeping its transparency. The quality of the thumbnail is pretty bad though.. but it is transparent.

$image = ImageCreateFromGIF('transparentimage.gif');
$img_width = ImagesX($image);
$img_height = ImagesY($image);

$new_width = '100';
$new_height = ($new_width * $img_height) / $img_width;

$resized = imagecreatetruecolor($new_width, $new_height);

$colorTransparent = imagecolortransparent($image);
imagepalettecopy($image, $resized);
imagefill($resized, 0, 0, $colorTransparent);
imagecolortransparent($resized, $colorTransparent);

imagetruecolortopalette($resized, true, 256);

imagecopyresized($resized, $image, 0, 0, 0, 0, $new_width, $new_height, $img_width, $img_height);

Mikasto (15-Aug-2007 12:53)

To resize transparent PNG (if image is transparent & ImageColorTransparent() returns -1):
1) create a new image with the new sizes
2) make the new image all transparent
3) turn off the alpha blending for the new image (to keep the alpha channel when copy data)
4) do copyresampled or copyresized into new image

PHP code:
// 1
$im2 = ImageCreateTrueColor($w, $h);
// 2
ImageColorTransparent($im2, ImageColorAllocate($im2, 0, 0, 0));
// 3
ImageAlphaBlending($im2, false);
// 4
ImageCopyResampled($im2, $im, 0, 0, 0, 0, $w, $h, ImageSX($im), ImageSY($im));

erik at vectorsector dot net (13-Jul-2007 05:20)

This script creates transparency for a unspecific RBG color for an already created PNG image.  It also includes script of overlay text that does not get ruined in the process.

<?php

header("Content-type: image/png");
$image = imagecreatetruecolor(250, 250);
$string = $_GET['text'];
$im     = imagecreatefrompng("dynIcon.png");
$img = imagecreatetruecolor(16,16);
$orange = imagecolorallocate($im, 220, 210, 60);
$bg_color = imagecolorat($im,1,1);
$px     = (imagesx($im) - 3 * strlen($string)) / 2;
imagecolortransparent($im, $bg_color);
imagestring($im, 3, $px, 5, $string, $orange);
imagepng($im);
imagedestroy($im);

?>

Use $bg_color = imagecolorat($im,1,1); for instance, if you made the transparent color in photoshop by clearing out all the color leaving you with the checkered background showing you it's empty.

cinymini (14-Dec-2006 07:17)

When you use palette images (created with imagecreate()), the first color allocated is the background color. This color cannot be used for transparency. So if you want to make the background transparent, first allocate a dummy background color, then allocate the real background color and declare this is as transparent.

glenn at bengeweb dot co dot nz (18-Nov-2006 04:03)

in reference to webmaster at webnetwizard dotco dotuk who had a rather complicated method of determining if a GIF had any transparency set ...

imagecolortransparent will return -1 if no transparency is found.

eg:

$transColorIndexMain = imageColorTransparent($mainImgObj);
if ($transColorIndexMain >= 0 ) {
       # GIF has transparency ... ;
}

Current PHP Version: 4.4.4
[GD Version] => bundled (2.0.28 compatible)

Blaine Ehrhart (07-Jul-2006 10:59)

This script creates transparency for a specific RBG color for an already created GIF image.
<?php
    $im = imagecreatefromgif('trans.gif');
    $img = imagecreatetruecolor(16,16);
    $trans = imagecolorallocate($img,255,99,140);
    imagecolortransparent($img,$trans);
    imagecopy($img,$im,0,0,0,0,16,16);
    imagetruecolortopalette($img, true, 256);
    imageinterlace($img);
    imagegif($img,'trans.gif');
    imagedestroy($img);
?>

Joachim Kruyswijk (20-Oct-2005 12:20)

A negative color number will turn antialiasing off, but even a positive number chosen for transparency may affect antialiasing. If the text (created with imagettftext) in your image looks horrible, try using a higher color number.

contact at wdschools dot com (19-Oct-2005 05:02)

Transparent GIF w/ text from TTF Font
-------------------------------------
$image = imagecreatetruecolor(192, 36);
$trans_color = imagecolorallocate($image, 255, 0, 0);
$color = imagecolorallocate($image, 255, 255, 255);
imagecolortransparent($image, $trans_color);
imagettftext($image, 10, 0, 10, 23, $color, "impact.ttf", " MENU ITEM");
imagegif($image, "output.gif");
imagedestroy($image);

ingrid (09-Jun-2005 05:37)

This script should take an animated GIF whit a white background transparancy, put some white=transparant text on it, and can be used in any page using the filename and the normal image tags.

Everything works well, exept the animation. The GIF animation stands still. Don't know how to keep the animation  animated. Is it possible in PHP?

<?php

$TextFile = "teller.txt";
$Count = trim(file_get_contents($TextFile));
$FP = fopen($TextFile, "r");
$Count=fgets($FP, 4096);
fclose ($FP);
settype($Count, "integer");
$Count++;
if ($FP = fopen ($TextFile, "w")){
fwrite ($FP, $Count);
fclose ($FP);
}

$image = "blad.gif";
$im    = imagecreatefromgif($image);
$white = imageColorAllocate ($im, 255, 255, 255);
$trans = imagecolortransparent($im,$white);
$hit = "$Count";
$ip = $_SERVER["REMOTE_ADDR"];

ImageString($im, 2, 30, 60,  " je bent bezoeker ", $white);
ImageString($im, 3, 20, 80, " $ip.$hit", $trans);

header("Content-Type: image/gif");
Imagegif($im,'',100);
ImageDestroy ($im);

?>

thomas at nindel dot net (20-Apr-2005 06:02)

I wanted to have non-rectangular images being displayed on various website-backgrounds. piece of cake with png-24 and sane browsers, but not with IE. GIF-files are useless since they tend to have ugly edges.

So that's what i came up with, a script to merge a given PNG-24 against a background-image. The script only merges areas of partial transparency (think anti-aliased edges) of the PNG onto the background-image, leaving 100% transparent areas as they are. output is a 256-color gif with transparency.

<?PHP
  function alphaishMerge(&$img_unten, &$img_oben, &$transCol) {
    $sx = imagesx($img_unten);
    $sy = imagesy($img_oben);
   
    // just be sure
    imagealphablending($img_unten, TRUE);
    imagealphablending($img_oben, TRUE);
   
    // imagecopy respects alpha channels
    imagecopy($img_unten, $img_oben, 0, 0, 0, 0, $sx, $sy);
   
    for ($x = 0; $x < $sx; $x++) {
      for ($y = 0; $y < $sy; $y++) {
       
        // get RGBA of upper image
        $pxloben = imagecolorat($img_oben, $x, $y);
        $pxloben = imagecolorsforindex($img_oben, $pxloben);
       
        if ($pxloben['alpha'] == 127) {
          // if this pixel is fully transparent...
          // ...set it to the transparent color
          imagesetpixel($img_unten,$x,$y,$transCol);
        }
      }
    }
  }
 
  // images have to be the same size
  $bg_file = "background.jpg";
  $png_file ="kauscha.png";

  // background-image (jpg)
  $img_bg = imagecreatefromjpeg($bg_file);
 
  // image which is supposed to be put on the background (PNG-24)
  $img_png = imagecreatefrompng($png_file);
 
  // This color is the one getting transparent in the gif-file
  $transCol = imagecolorallocate($img_bg, 0, 0, 0);

  // magic
  alphaishMerge($img_bg, $img_png, $transCol);
 
  // reduce color depth
  imagetruecolortopalette($img_bg, FALSE, 255);
 
  // make it transparent
  $transCol = imagecolortransparent($img_bg, $transCol);
 
  header("Content-type: image/gif");
  imagegif($img_bg);
?>

i hope thats useful for anyone.

partyheld at HATESPAMgmail dot com (31-Mar-2005 05:35)

Fred wrote:
<?php
$file['signatur']=      substr($result,0,3);
             $file['version']=        substr($result,3,3);
             $file['width']=          ord(substr($result,6,1))+ord(substr($result,7,1))*256;
             $file['height']=        ord(substr($result,8,1))+ord(substr($rsult,9,1))*256;
             $file['flag']=          ord(substr($result,10,1))>>7;
             $file['trans_red']=      ord(substr($result,ord(substr($result,11))*3,1));
             $file['trans_green']=    ord(substr($result,ord(substr($result,11))*3+1,1));
             $file['trans_blue']=    ord(substr($result,ord(substr($result,11))*3+2,1)) ;
?>

You should write such code like this:

<?php
   $file = array(
      "signatur"           => substr ($result, 0, 3),
      "version"            => substr ($result, 3, 3),
      "width"              => ord (substr ($result, 6, 1)) + ord (substr ($result, 7, 1)) * 256,
      "height"             => ord (substr ($result, 8, 1)) + ord(substr ($result, 9, 1)) * 256,
      "flag"               => ord (substr ($result, 10, 1)) >> 7,
      "trans_red"          => ord (substr ($result, ord (substr ($result, 11)) * 3,1)),
      "trans_green"        => ord (substr ($result, ord (substr($result, 11)) * 3 + 1, 1)),
      "trans_blue"         => ord (substr ($result, ord (substr($result, 11)) * 3 + 2, 1))
      );
?>

And there's a typo in line 4, sayin "rsult" instead of "result". I've got no time for checking your code any further, sorry.

raiserle (28-Mar-2005 04:52)

it goes also more simply
i rather work with arrays
<?php
if(!function_exists('gif_info'))
{
    function gif_info($filename)
    {
             $fp=                     fopen($filename,'rb');
             $result=                 fread($fp,13);
             $file['signatur']=       substr($result,0,3);
             $file['version']=        substr($result,3,3);
             $file['width']=          ord(substr($result,6,1))+ord(substr($result,7,1))*256;
             $file['height']=         ord(substr($result,8,1))+ord(substr($rsult,9,1))*256;
             $file['flag']=           ord(substr($result,10,1))>>7;
             $file['trans_red']=      ord(substr($result,ord(substr($result,11))*3,1));
             $file['trans_green']=    ord(substr($result,ord(substr($result,11))*3+1,1));
             $file['trans_blue']=     ord(substr($result,ord(substr($result,11))*3+2,1)) ;
             fclose($fp);
             return $file;
    }
}
print_r(gif_info($_FILES['files']['temp_name']));
?>

talkback at codesponge dot com (16-Mar-2005 11:41)

Only one color may be transparent in one image.  The last call to imagecolortransparent will be the color that is set to transparent.

I am processing button images that have a slightly different fill color than the background color outside the border of the button. I was hoping that I could just make both of those colors transparent and solve the problem.

Hope this tidbit of info will save you some time.

fred at webblake dot net (14-Jan-2005 04:17)

Wow! I am actually surprized there are no functions to retrieve transparency information from the image. I assume I'm not missing anything since there are all kinds of notes about how to get around this limitation. At any rate, here is some code to read the gif file and retrieve the missing information. The code will speak volumes.

<?php

    class GifInfo
    {
        var $m_transparentRed;
        var $m_transparentGreen;
        var $m_transparentBlue;
        var $m_signature;
        var $m_version;
        var $m_width;
        var $m_height;
        var $m_width;
        var $m_height;
        var $m_colorFlag;
        var $m_backgroundIndex;
       
       
        function GifInfo($filename)
        {

            $fp                         = fopen($filename,"rb");
            $result                     = fread($fp,13);
            $this->m_signature     = substr($result,0,3);
            $this->m_version         = substr($result,3,3);
            $this->m_width         = ord(substr($result,6,1)) + ord(substr($result,7,1)) * 256;
            $this->m_height         = ord(substr($result,8,1)) + ord(substr($result,9,1)) * 256;
            $this->m_colorFlag    = ord(substr($result,10,1)) >> 7;
            $this->m_background     = ord(substr($result,11));
   
            if($this->m_colorFlag)
            {
                $tableSizeNeeded = ($this->m_background + 1) * 3;
                $result = fread($fp,$tableSizeNeeded);
                $this->m_transparentRed     = ord(substr($result,$this->m_background * 3,1));
                $this->m_transparentGreen     = ord(substr($result,$this->m_background * 3 + 1,1));       
                $this->m_transparentBlue     = ord(substr($result,$this->m_background * 3 + 2,1));           
            }
            fclose($fp);
        }
    }
?>

And to use this class....

<?php
   $size = getimagesize($userfile);

   $img2 = ImageCreate($w,$h);           
   $gi = new GifInfo($userfile);

   if($gi->m_version == '89a' && $gi->m_colorFlag == 1)
   {
      $transparent = imagecolorallocate($img2,
      $gi->m_transparentRed,
      $gi->m_transparentGreen,
      $gi->m_transparentBlue);           

      imagecolortransparent ($img2,$transparent);
   }
?>

webmaster at webnetwizard dotco dotuk (11-Jan-2005 09:24)

I'm feeling particularly altruistic today, so here is the code to accompany the text I submitted about a script that 'intelligently' detects if an uploaded GIF has transparency or not, and creates a thumbnail accordingly:

    if (move_uploaded_file($_FILES['userfile']['tmp_name'], $uploadfile))
    {
      $note = "Image was successfully uploaded.\n";
      // Now create thumbnail version of the uploaded image and save it to
      // folder "$fixPath/images/thumbs". First, we need to create a
      // resource "handle" for a copy of the uploaded image
      $img_error = false;
      list($width, $height, $type) = getimagesize($uploadfile);
      switch($type) // Allowed types: image/gif,image/jpeg,image/x-png
      {
        case 1: // GIF
          $src = @imagecreatefromgif($uploadfile);
          if (!$src)
            $img_error = true;
          break;
        case 2: // JPEG
         .
         .
         .
      case 3: // PNG
        .
        .
        .
       default:
          $img_error = true;
      }
      // resource handle for source image now in $src
      // Now calculate scaling factor and put in $sf
      if(!$img_error)
      {
        if($width >= $height && $width > 100)
          $sf = $width / 100;
        elseif($height > 100)
          $sf = $height / 100;
        else
          $sf = 1;
        $newwidth = intval($width / $sf);
        $newheight = intval($height / $sf);
 
        switch($type) // Allowed types: image/gif,image/jpeg,image/x-png
        {
          case 1: // GIF
            $tpcolor = imagecolorat($src, 0, 0);
            // in the real world, you'd better test all four corners, not just one!
            $dest = imagecreate($newwidth, $newheight);
            // $dest automatically has a black fill...
            imagepalettecopy($dest, $src);
            imagecopyresized($dest, $src, 0, 0, 0, 0, $newwidth, $newheight,
              $width, $height);
            $pixel_over_black = imagecolorat($dest, 0, 0);
            // ...but now make the fill white...
            $bg = imagecolorallocate($dest, 255, 255, 255);
            imagefilledrectangle($dest, 0, 0, $newwidth, $newheight,
              $bg);
            imagecopyresized($dest, $src, 0, 0, 0, 0, $newwidth, $newheight,
              $width, $height);
            $pixel_over_white = imagecolorat($dest, 0, 0);
            // ...to test if transparency causes the fill color to show through:
            if($pixel_over_black != $pixel_over_white)
            {
              // Background IS transparent
              imagefilledrectangle($dest, 0, 0, $newwidth, $newheight,
                $tpcolor);
              imagecopyresized($dest, $src, 0, 0, 0, 0, $newwidth,
                $newheight, $width, $height);
              imagecolortransparent($dest, $tpcolor);
              imagegif($dest, "$fixPath/images/thumbs/$userfile");
            }
            else // Background (most probably) NOT transparent
              imagegif($dest, "$fixPath/images/thumbs/$userfile");
            break;
          case 2: // JPEG
          .
          .
          .
          case 3: // PNG
          .
          .
          .
            break;
        }
        imagedestroy($src);
        imagedestroy($dest);
      }
      else
        $note = "Error: Uploaded image but could not create thumbnail";
      header("location: $fixPath/index.php?next=$next&nb=$nb&userfile=$userfile");
    }
    else
      $note = "Could not find anything to upload\n";

webmaster at webnetwizard dotco dotuk (11-Jan-2005 02:09)

After much devious mindbending, I have found a way to test any GIF for presence of background transparency. This ability is essential for my application which uploads any of GIF, JPEG or PNG and simultaneously creates a thumbnail of identical image type and identical filename (full size and thumbnail versions being stored in different folders).
After uploading and moving the image in the usual way, a switch($image_type) statement ensures that the optimum code is used to generate the thumbnail; regardless of image type.
The problem with the GIF type is that those with transparent backgrounds need to be treated differently to those without. When I don't detect GIF transparency, I either end up with all transparent GIF's having black backgrounds, or all GIF's get converted to transparent background - even if they weren't transparent in the original.
But how to detect transparency in the original? It finally occurred to me that I could test for transparency programmatically by overlaying a copy of the original image over an all-black image, record the color value at particular pixel locations and then repeat the process by overlaying a copy of the original image over an all-white image, recording the color values at identical pixel locations and comparing these with the first set of values.
If the two sets of values correlate exactly, and if sensible sampling points are used, the image can be treated as non-transparent. If the two sets of values show differences, the image should be treated as having a transparent background.

emilus at galeria-m dot art dot pl (30-Sep-2004 10:02)

To resize or copy image (gif [with gd>=2.0.28] or png) with transparency.
-Take current transparency color
-create a new image with palette like old one and fill new image with transparent color
-set transparent color
-copy resized image

$colorTransparent = imagecolortransparent($im);
$im2 = imagecreate($new_w,$new_h);
imagepalettecopy($im2,$im);
imagefill($im2,0,0,$colorTransparent);
imagecolortransparent($im2, $colorTransparent);
imagecopyresized($im2,$im,0,0,0,0,$new_w,$new_h,$imsx,$imsy);

php_comment et 5mm de (27-Sep-2004 06:02)

In fact this function can be used for two purposes:

A.) to work with transparency while dealing with images in php (see watermark example)

B.) to create a partially transparent picture

For A.) one can work with truecolor images with some regulations, but B.) can only be used with palette-based images (= indexed = created with imagecreate not imagecreatetruecolor) and formats that support transparency (png, gif).

For instance if you want to cut out a color out of a give picture that is in truecolor, use the following method to first convert it to palette-based image, assign the transparency and give it to the browser as png:

<?
$img = imagecreatefromjpeg('test.jpg');
imagetruecolortopalette($img, false, 256); // convert

$white = imagecolorresolve($img, 255, 255, 255); // resolve given palette entry
imagecolortransparent($img, $white);

header("Content-type: image/png");
imagepng($img);
?>

shelley_hina at yahoo dot com (04-Mar-2004 07:35)

It took me a while to figure this out. I added visual web thumbnail preview graphic from http://www.thumbshots.org and http://www.thumbshots.com to my customer sites to visualize web pages. Then I needed to create a small blank transparent PNG image if the thumbshot is not available. You can do this easily using imagecolortransparent function. It came out really nice and fast. It's very cool stuff and highly recommended library for all your web site needs!

// Use GD library to create transparent color PNG image of the pixel size
$ImgGD = imagecreate(120, 90);
$ImgWhite = imagecolorallocate($ImgGD, 255, 255, 255);
imagefill($ImgGD, 0, 0, $ImgWhite);
imagecolortransparent($ImgGD, $ImgWhite);

// Capture STDOUT to buffer
ob_start();
imagepng($ImgGD);
$Image = ob_get_contents();
ob_end_clean();

// Remember to free your memory
imagedestroy($ImgGD);

// Print image to web browser.
print $Image

php at kybert dot com (14-Nov-2003 01:30)

i had problems with the example by sandhawk at spies dot com because my png overlay, and the jpeg canvas were using different color depths, so, this function corrects this:

[code]
function WatermarkImage($CanvasImage, $WatermarkImage /* MUST BE PHG */, $Opacity=10, $Quality=75)
{
    // create true color canvas image:
    $canvas_src = imagecreatefromjpeg($CanvasImage);
    $canvas_w = ImageSX($canvas_src);
    $canvas_h = ImageSY($canvas_src);
    $canvas_img = imagecreatetruecolor($canvas_w, $canvas_h);
    imagecopy($canvas_img, $canvas_src, 0,0,0,0, $canvas_w, $canvas_h);
    imagedestroy($canvas_src);    // no longer needed

    // create true color overlay image:
    $overlay_src = imagecreatefrompng($WatermarkImage);
    $overlay_w = ImageSX($overlay_src);
    $overlay_h = ImageSY($overlay_src);
    $overlay_img = imagecreatetruecolor($overlay_w, $overlay_h);
    imagecopy($overlay_img, $overlay_src, 0,0,0,0, $overlay_w, $overlay_h);
    imagedestroy($overlay_src);    // no longer needed

    // setup transparent color (pick one):
    $black   = imagecolorallocate($overlay_img, 0x00, 0x00, 0x00);
    $white   = imagecolorallocate($overlay_img, 0xFF, 0xFF, 0xFF);
    $magenta = imagecolorallocate($overlay_img, 0xFF, 0x00, 0xFF);   
    // and use it here:
    imagecolortransparent($overlay_img, $white);

    // copy and merge the overlay image and the canvas image:
    imagecopymerge($canvas_img, $overlay_img, 0,0,0,0, $overlay_w, $overlay_h, $Opacity);

    // output:
    header("Content-type: image/jpeg");
    imagejpeg($canvas_img, '', $Quality);

    imagedestroy($overlay_img);
    imagedestroy($canvas_img);
}

// call function with opcity set to 50% and 95% quality
WatermarkImage("canvas.jpg", "overlay.png", 50, 95);

[/code]

creator79>>web>>de (09-Oct-2003 02:44)

Hi!
I'm using GDLib 1.6.3 so far I know.
You can have transparency on any defined color on any image type when using the imagecolorclosest($im, $R, $G, $B) function instead of imagecolorallocate() or imagecolorexact().

calar at gamigo dot de (02-Aug-2003 02:53)

ok some works...

i had a test-sytem with GDLib, phpinfo shows me this version:
"GD Version  2.0 or higher" so far no porblems with: imageColorTransparent

Then we had to copy ouer codes to another sever on this server phpinfo shots me version:
"GD Version  bundled (2.0.12 compatible)"

The jpg was wrong and nothing was transparent.
The point is, you have to use: imagecopymerge

Don't if its true on any system just work on
SUSE 8.2
PHP 4.3.2

cladiniz at zipmail dot com dot br (18-Mar-2003 02:19)

If you have a transparent PNG , in PHP 4.3.1 , GD 2.0 , you don't need to set the transparency anymore , it's automatic ...

sandhawk at spies dot com (06-Mar-2003 07:04)

here's a little snippet of code that i got for getting images to overlay with transparency(based off text overlay above).

$olay_img = imagecreatefromPNG("overlay.png); //NOTE I recomment you use png for this, artifacts from jpeg images can look bad when you overlay them
$src_img = ImageCreateFromJPEG("image.jpg");
$src_w = ImageSX($src_img);
$src_h = ImageSY($src_img);

$can_img = imagecreatetruecolor($src_w, $src_h);

$black = ImageColorAllocate ($olay_img, 0, 0, 0);

ImageColorTransparent($olay_img, $black);

imagecopy($can_img, $src_img, 0,0,0,0, $src_w, $src_h);
imagecopymerge($can_img, $olay_img, 0,0,0,0, ImageSX($olay_img), ImageSY($olay_img),100); //Imagecopy won't work, you must used imagecopymerge

ImageJPEG($can_img,'',100);

imagedestroy($src_img);
imagedestroy($olay_img);
imagedestroy($can_img);

Jonatan (30-Dec-2002 06:35)

I have found that ImageColorTransparent() works on true color images if and only if the transparent color is black.
(PHP 4.2.3/GD 2.0)

marshall.AT.byterage.net (05-May-2002 03:50)

In response to the note above...

ImageColorTransparent() does work on TrueColor images.  I have it working myself but I do remember having to add an extra step somewhere.  Anyways, here is how I overlay text on a jpeg.  Don't forget, you need GD 2.x for true color to work.  This example requires TTF support also.

//
// get src image and dimensions
$src_img = ImageCreateFromJPEG("foo.jpg");
$src_w = ImageSX($src_img);
$src_h = ImageSY($src_img);
//
// create empty true color canvas, def bg is black
$txt_img = ImageCreateTrueColor($src_w,$src_h);
//
// define colors
$white = ImageColorAllocate ($txt_img, 255, 255, 255);
$black = ImageColorAllocate ($txt_img, 0, 0, 0);
//
// add your white text
ImageTTFText ($txt_img, 80, 25, 65, 350, $white, "impact.ttf", "Kung Fu");
//
// make black bg transparent
ImageColorTransparent($txt_img, $black);
//
// merge text image onto src image
ImageCopyMerge($src_img,$txt_img,0,0,0,0,$src_w,$src_h,30); // 30% opacity

'Now' you can do resizing or whatever and output it.  You need to create yet another blank image to resample.  (Actually you can resize the image before the text overlay step with some small mods, but its REALLY messy if you want the output size to be dynamic)

//
// create empty true color canvas for resizing.
$dst_img = ImageCreateTrueColor(100,100);
//
// resize
ImageCopyResampled($dst_img,$src_img,0,0,0,0,100,100,$src_w,$src_h);
//
// output to browser.
ImageJPEG($dst_img,'',70);   // quality 70

If someone could tell me a shorter way to do this, that would be sweet.  The way it is now, it just feels like there is one too many steps to get this done.  But I am glad it works at all!

(07-Dec-2001 03:18)

when a color is defined as transparent, anytime that color is used in another function (before or after transparency definition) will be transparent

ex:
$red = ImageColorAllocate ($im, 233, 14, 91);
$blue = ImageColorAllocate ($im, 0x20, 0x60, 0xaa);
imagefilledarc ($im, 100, 100, 80, 80, 0, 60, $blue, IMG_ARC_PIE);//arc is transparent even though is not defined yet
$trans=imagecolortransparent($im,$blue);//affects all occurances of blue, before and after this line

ALSO:
ImageString ($im, 10, 5, 5,  "Transparent Text String", $blue);
---is equivalent to----
ImageString ($im, 10, 5, 5,  "Transparent Text String", $trans);