need help preserving transparancy when resampling images in GD

[zeb]

I'm trying to resize an image on the fly, but if the image contains transparency, it isn't preserved. I'm a bit confused by all the various alpha related GD functions. Here's what I have. I'm sure I need to add something around the imageCopyResampled part.

$info = getimagesize( $file );

//-----------------
// create the image
//-----------------
switch ( $info[2] )
	{
	case 1: $im_org = imageCreateFromGIF( $file );	break;
	case 2: $im_org = imageCreateFromJPEG( $file );	break;
	case 3: $im_org = imageCreateFromPNG( $file );	break;
	}

//--------------------------------
// do we have to resize the image?
//--------------------------------
if ( $info[0] > $maxWidth )
	{
	$width = $maxWidth;
	$height = round( ( $width / $info[0] ) * $info[1] );
	$im_new = imageCreateTrueColor( $width, $height );
	imageCopyResampled( $im_new, $im_org, 0, 0, 0, 0, $width, $height, $info[0], $info[1]);
	}
else
	{
	$im_new = $im_org;
	}

//------------------------------
// send the image to the browser
//------------------------------
switch ( $info[2] )
	{
	case 1: 
		{
		@header("Content-type: image/gif");
		imageTrueColorToPalette( $im_new, TRUE, 256 );
		imageGIF( $im_new );
		break;
		}
	case 2:
		{
		@header("Content-type: image/jpeg");
		imageJPEG( $im_new );
		break;
		}
	case 3:
		{
		@header("Content-type: image/png");
		imagePNG( $im_new );
		break;
		}
	}

imageDestroy( $im_org );
imageDestroy( $im_new );

[zeb]

I think I solved the transparency for PNG images by adding the following before the imageCopyResampled function:

if ( $info[2] == 3 ) // if type is PNG
	{
	imagealphablending( $im_new, FALSE );
	imagesavealpha( $im_new, TRUE );
	}

But I still don't have transparency for GIFs.

Any ideas?

[zeb]

I think I figured it out, and since I couldn't find a solution anywhere else, I figured I'd post what I found out here for anyone else who needs help with this.

Basically, for GIF images, in order to preserve the transparency in the new resized image, you can't use a true color image as a destination. You need to create a regular palette image as the destination image and designate the first color as transparent.

$info = getimagesize( $file ); 

//----------------- 
// create the image 
//----------------- 
switch ( $info[2] ) // which type of image is it?
    { 
    case 1: $im_org = imageCreateFromGIF( $file );    break; 
    case 2: $im_org = imageCreateFromJPEG( $file );    break; 
    case 3: $im_org = imageCreateFromPNG( $file );    break; 
    } 

//-----------------
// resize the image
//-----------------
if ( $info[2] == 1 ) // create a palette image for GIFs
	{
	$im_new = imageCreate( $newWidth, $newHeight );
	$transparent = imagecolorallocatealpha( $im_new, 255, 255, 255, 127 );
	imagecolortransparent( $im_new, $transparent );
	}
else // create a true color image for PNGs and JPEGs
	{
	$im_new = imageCreateTrueColor( $newWidth, $newHeight );
	}
if ( $info[2] == 3 ) // alphablending OFF and savealpha ON for PNGs
	{
	imagealphablending( $im_new, FALSE );
	imagesavealpha( $im_new, TRUE );
	}
imageCopyResampled( $im_new, $im_org, 0, 0, 0, 0, $newWidth, $newHeight, $info[0], $info[1]);

//------------------------------ 
// send the image to the browser 
//------------------------------ 
switch ( $info[2] ) 
    { 
    case 1: 
        { 
        @header("Content-type: image/gif"); 
        imageGIF( $im_new ); 
        break; 
        } 
    case 2: 
        { 
        @header("Content-type: image/jpeg"); 
        imageJPEG( $im_new ); 
        break; 
        } 
    case 3: 
        { 
        @header("Content-type: image/png"); 
        imagePNG( $im_new ); 
        break; 
        } 
    } 

imageDestroy( $im_org ); 
imageDestroy( $im_new );