imagecolortransparent

(PHP 3, 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()image 图像中的透明色设定为 colorimageimagecreatetruecolor() 返回的图像标识符,colorimagecolorallocate() 返回的颜色标识符。

注: 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。

注: 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。


add a note add a note User Contributed Notes
Blaine Ehrhart
07-Jul-2006 05:59
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 07:20
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
20-Oct-2005 12:02
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
10-Jun-2005 12:37
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
21-Apr-2005 01:02
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
01-Apr-2005 01:35
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
29-Mar-2005 12:52
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
17-Mar-2005 07:41
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
15-Jan-2005 12:17
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
12-Jan-2005 05:24
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
     $note = "Could not find anything to upload\n";
webmaster at webnetwizard dotco dotuk
11-Jan-2005 10:09
After much devious mindbending, I have found a way to test any GIF for presence of background transparency. This ability is essential for my application which uploads any of GIF, JPEG or PNG and simultaneously creates a thumbnail of identical image type and identical filename (full size and thumbnail versions being stored in different folders).
After uploading and moving the image in the usual way, a switch($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
01-Oct-2004 05:02
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
28-Sep-2004 01:02
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
05-Mar-2004 03:35
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 09:30
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 09:44
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 09:53
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 10:19
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 03:04
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
31-Dec-2002 02:35
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 10:50
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 11:18
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);