[rrd-users] alpha channel on rrdtool PNG vs. TCPDF (Solved)

Valter Douglas Lisbôa Jr. douglas at trenix.com.br
Sun Jun 29 18:21:15 CEST 2008

I solved it! So, I'm posting the solution for others with a similar problem 
(Some versions of IE appear can't be capable to handle a PNG with 

It's a snip of my PHP OO code.

---------------------- snip ----------------------
// Creates a PDF with the graphs requireds.
public function getPDF() {
  try {
    $pdf = new TCPDF();

    ... // A lot of boring PDF preparation code

    // Temporary file
    $png = tempnam("../tmp/", "graph");

    // Calls the rrdtool command to generate the PNG
    $this->getCPU($png, ... other parameters ...); // 

    // Load, Remove all alpha and save in a new file
    $img =  ImageCreateFromPNG($png);
    imageAlphaBlending($img, false); 
    imageSaveAlpha($img, false);
    imagePNG($img, "$png.png");

    // Load to PDF
    $pdf->Image("$png.png", 30, 50);

    // Remove all temporaries

    // Put PDF on screen

  } catch(Exception $err) {
    throw new Exception('Graph Exception: ' . $err->getMessage());
---------------------- snip ----------------------

The tip is using imageAlphaBlending + imageSaveAlpha. The file size drops from 
32KB to 21KB (better for me, I botter for PDF size ;-) ) and loads normally 
on TCPDF. 

Three hours of research before a I send the first post, more some minutes 
to "google" the solution after that! Never Give up! :-D

If someone has another solution, it will be welcome. 

On Sunday 29 June 2008 12:39:09 Valter Douglas Lisbôa Jr. wrote:
> Hello All!
> I'm new on this list, and this is my first post.
> Creating a System to load the graph generated in PNG format from rrdtool
> with PHP 5, I was very sucefull. However, when I try to put it on a PDF
> utilizing TCPDF 3.1.001 PHP class, I got a error.
> TCPDF error: Alpha channel not supported: file.png
> This class has a limitation from loading PNG with transparent colors, it's
> a known bug not corrected yet, and this is the only format in common with
> rrdtool. So, I try to remove the PNG's alpha channel by rrdtool, definning
> every color with -c or in LINE/AREA/etc with the solid attribute (FF) on
> the end of color. It wasn't exactly a success :-( the error continues.
> Then I "googling" for PHP functions to find a way to remove the alpha
> channel, I already try to detect if exists a color with
> imagecolortransparent(), with another failure (it returns -1).
> Going to the point! How can I generate with rrdtool 1.2.x a PNG without a
> alpha channel? Or does anyone can point me the way to do this with another
> software on-the-fly?
> Thanks in advance

Valter Douglas Lisbôa Jr.
Trenix - IT Solutions
"Nossas Idéias, suas Soluções!"
contato at trenix.com.br
Tel. +55 19 3402.2957
Cel. +55 19 9183.4244

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