Transparent PNGs: Merging

Hi All,

I apologise if this is a newbie post; i'm new to transparent graphics
(PNGs in my case).

I have a transparent PNG on disk, which I want PHP to load into memory
and add some text to ("watermarking", I guess). This seems to be what
is achieved @ http://php.ca/manual/en/image.examples.merged-watermark.php

I have taken the following code almost entirely from the manual, but
can not understand what I have done wrong:


//Create the image
$img = @imagecreatetruecolor($width, $height)
or die("Cannot Initialize new GD image stream");

//Make it transparent
imagesavealpha($img, true);
$trans_colour = imagecolorallocatealpha($img, 0, 0, 0, 127);
imagefill($img, 0, 0, $trans_colour);

//Get the text color
$text_color = imagecolorallocate($img, 255, 0, 0);

//Draw the string
imagestring($img, $font_size, 0, 0, $string, $text_color);

// Load background image, find position, print
$img2 = imagecreatefrompng('xxx.png');
$yoffset = (imagesx($img2)/2) - (imagesx($img)/2);
imagecopymerge($img2, $img, $yoffset, 5, 0, 0, imagesx($img),
imagesy($img), 100);

// Output the merged images
header ("Content-type: image/png");
imagepng($img2);


This code prints the background image with transparancy removed with a
light grey, and the text image in red on a black background in the
correct position.
If I change it to imagepng($img), the text image is printed correctly
(transparency and all)

Suggestions appreciated, i'm lost!

Many thanks,

Alex

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Re: Transparent PNGs: Merging

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Content-Type: text/plain
Content-Transfer-Encoding: 7bit

On Sat, 2009-12-12 at 05:02 +0000, Alex Davies wrote:

> Hi All,
>
> I apologise if this is a newbie post; i'm new to transparent graphics
> (PNGs in my case).
>
> I have a transparent PNG on disk, which I want PHP to load into memory
> and add some text to ("watermarking", I guess). This seems to be what
> is achieved @ http://php.ca/manual/en/image.examples.merged-watermark.php
>
> I have taken the following code almost entirely from the manual, but
> can not understand what I have done wrong:
>
>
> //Create the image
> $img = @imagecreatetruecolor($width, $height)
> or die("Cannot Initialize new GD image stream");
>
> //Make it transparent
> imagesavealpha($img, true);
> $trans_colour = imagecolorallocatealpha($img, 0, 0, 0, 127);
> imagefill($img, 0, 0, $trans_colour);
>
> //Get the text color
> $text_color = imagecolorallocate($img, 255, 0, 0);
>
> //Draw the string
> imagestring($img, $font_size, 0, 0, $string, $text_color);
>
> // Load background image, find position, print
> $img2 = imagecreatefrompng('xxx.png');
> $yoffset = (imagesx($img2)/2) - (imagesx($img)/2);
> imagecopymerge($img2, $img, $yoffset, 5, 0, 0, imagesx($img),
> imagesy($img), 100);
>
> // Output the merged images
> header ("Content-type: image/png");
> imagepng($img2);
>
>
> This code prints the background image with transparancy removed with a
> light grey, and the text image in red on a black background in the
> correct position.
> If I change it to imagepng($img), the text image is printed correctly
> (transparency and all)
>
> Suggestions appreciated, i'm lost!
>
> Many thanks,
>
> Alex
>


The only thing I can obviously see is that you've told it to ignore
transparency on $img2 by not asking it to preserve it (the default is to
ignore). PNG doesn't handle transparency in the same way a GIF does,
each pixel can have a varying degree of opacity, which allows whatever
is beneath it to show through. Add the imagesavealpha($img, true); line
for $img2 and see what that does for you.

Thanks,
Ash
http://www.ashleysheridan.co.uk



--=-BtM7qijR0/JXHF22mZQm--

Re: Transparent PNGs: Merging

--000e0cd1b12edb57a6047a888143
Content-Type: text/plain; charset=ISO-8859-1

Hi Ash,

Thanks for your suggestion. Unfortunately,that did not help but i've found a
post via Google which gave a simple (and slightly counter-intuitive)
solution - replace

imagecopymerge($img2, $img, $yoffset, 5, 0, 0, imagesx($img), imagesy($img),
100);
with
imagecopy($img2, $img, $yoffset, 5, 0, 0, imagesx($img), imagesy($img));

And it works :)

It seems imagecopymerge does not work well with PNGs and Alpha Channels.

Many thanks for your help,

Alex

On Sat, Dec 12, 2009 at 11:20 AM, Ashley Sheridan
wrote:

> On Sat, 2009-12-12 at 05:02 +0000, Alex Davies wrote:
>
> Hi All,
>
> I apologise if this is a newbie post; i'm new to transparent graphics
> (PNGs in my case).
>
> I have a transparent PNG on disk, which I want PHP to load into memory
> and add some text to ("watermarking", I guess). This seems to be what
> is achieved @ http://php.ca/manual/en/image.examples.merged-watermark.php
>
> I have taken the following code almost entirely from the manual, but
> can not understand what I have done wrong:
>
>
> //Create the image
> $img = @imagecreatetruecolor($width, $height)
> or die("Cannot Initialize new GD image stream");
>
> //Make it transparent
> imagesavealpha($img, true);
> $trans_colour = imagecolorallocatealpha($img, 0, 0, 0, 127);
> imagefill($img, 0, 0, $trans_colour);
>
> //Get the text color
> $text_color = imagecolorallocate($img, 255, 0, 0);
>
> //Draw the string
> imagestring($img, $font_size, 0, 0, $string, $text_color);
>
> // Load background image, find position, print
> $img2 = imagecreatefrompng('xxx.png');
> $yoffset = (imagesx($img2)/2) - (imagesx($img)/2);
> imagecopymerge($img2, $img, $yoffset, 5, 0, 0, imagesx($img),
> imagesy($img), 100);
>
> // Output the merged images
> header ("Content-type: image/png");
> imagepng($img2);
>
>
> This code prints the background image with transparancy removed with a
> light grey, and the text image in red on a black background in the
> correct position.
> If I change it to imagepng($img), the text image is printed correctly
> (transparency and all)
>
> Suggestions appreciated, i'm lost!
>
> Many thanks,
>
> Alex
>
>
>
> The only thing I can obviously see is that you've told it to ignore
> transparency on $img2 by not asking it to preserve it (the default is to
> ignore). PNG doesn't handle transparency in the same way a GIF does, each
> pixel can have a varying degree of opacity, which allows whatever is beneath
> it to show through. Add the imagesavealpha($img, true); line for $img2 and
> see what that does for you.
>
>
> Thanks,
> Ash
> http://www.ashleysheridan.co.uk
>
>
>


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Alex Davies

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Re: Transparent PNGs: Merging

At 5:02 AM +0000 12/12/09, Alex Davies wrote:
>-snip-
>
>Suggestions appreciated, i'm lost!
>
>Many thanks,
>
>Alex

Watermark?

Try this:

http://webbytedd.com/b/watermark/

The code is there and the dog is actual size.

Cheers,

tedd
--
-------
http://sperling.com http://ancientstones.com http://earthstones.com

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