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Bildverarbeitung und -generierung




Bildbearbeitung und GD

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mac_doggie at hotmail dot com
28.05.2010 16:50
A way to read the color of a pixel:

= imagecreatefrompng("image1.png");
$w = imagesx($img);
$h = imagesy($img);
$y=0;$y<$h;$y++) {
$x=0;$x<$w;$x++) {
$rgb = imagecolorat($img, $x, $y);
$r = ($rgb >> 16) & 0xFF;
$g = ($rgb >> 8) & 0xFF;
$b = $rgb & 0xFF;        
"<br />\r\n";

[EDIT BY thiago: merged two notes from same submitter.]
rmayo100 at yahoo dot com
18.05.2010 17:05
I use GD to create graphs of data that exists in my system.  I use a link like this to place the graph image on my page:
      <img src="image.php" name="Image">

And this works just fine.  Image.php acquires the data to be graphed and creates a png image with it. (And is even able to do it very quickly.)

However, I would also like to have external access that data.  Unfortunately, it's is acquired by the graphing function from a UDP broadcast stream and I have no idea how to make it available outside that file (or how to capture it twice, perhaps).

I've had exactly no luck trying to implement a global variable, I suspect, because global variables really aren't global and their scope doesn't span multiple files.

I don't know if this is the right venue for this post, but I'm stumped so far and I had to post it somewhere.

mail at ecross dot nl
3.04.2010 17:31
hello there,
i made a function to create a gradient image.

gradient(int image_width, int image_height,
int start_red, int start_green, int start_blue,
int end_red, int end_green, int end_blue,
bool vertical)

function gradient($image_width, $image_height,$c1_r, $c1_g, $c1_b, $c2_r, $c2_g, $c2_b, $vertical=false)
// first: lets type cast;
$image_width = (integer)$image_width;
$image_height = (integer)$image_height;
$c1_r = (integer)$c1_r;
$c1_g = (integer)$c1_g;
$c1_b = (integer)$c1_b;
$c2_r = (integer)$c2_r;
$c2_g = (integer)$c2_g;
$c2_b = (integer)$c2_b;
$vertical = (bool)$vertical;

// create a image
$image  = imagecreatetruecolor($image_width, $image_height);

// make the gradient
for($i=0; $i<$image_height; $i++)
$color_r = floor($i * ($c2_r-$c1_r) / $image_height)+$c1_r;
$color_g = floor($i * ($c2_g-$c1_g) / $image_height)+$c1_g;
$color_b = floor($i * ($c2_b-$c1_b) / $image_height)+$c1_b;

$color = ImageColorAllocate($image, $color_r, $color_g, $color_b);
imageline($image, 0, $i, $image_width, $i, $color);

# Prints out all the figures and picture and frees memory
header('Content-type: image/png');

$vertical){$image = imagerotate($image, 90, 0);}
jordan at jkdesign dot org
8.09.2009 0:09
Building on Ashley's example, here's an example of some code that grabs an existing image file and outputs an html img tag with the contents. I found it useful because I needed to not broadcast the filenames.

= 'images/01.png';
$image = imagecreatefrompng($file);
imagealphablending($image, false);
imagesavealpha($image, true);

// start buffering
$contents ob_get_contents();

"<img src='data:image/png;base64,".base64_encode($contents)."' />";

scurvysquid at yahoo dot com
4.05.2009 21:08
to address Thomas' note about exif data, exif is only valid for .tiff and .jpg files.    As always, it's up to the individual to make the call but I personally would prefer to create an abstraction layer to work for all images, and relying on exif data means you need to limit your allowed image types.  I've heard some great things about the GD library and found them to all be true in my own use of it, losing the nominally useful data specific to jpegs and pngs is not a sufficient reason alone to convince me to use imagemagick instead.
10.12.2008 23:05
You know, maybe this goes without saying, but I thought I would drop a note in here.  When developing code to resize images, it is best not to use GD.  When using the current GD methodologies, you are reading content from an image and manipulating it.  By then writing that content to a brand new file, you are losing the EXIF data.

For purposes when you want to retain EXIF data, it is recommended that you compile in and use the PECL Imagick extension.  It has great resizing methods built right in and the EXIF data is retained.
code at ashleyhunt dot co dot uk
24.10.2008 3:02
I have been looking to send the output from GD to a text string without proxying via a file or to a browser.

I have come up with a solution.

This code buffers the output between the ob_start() and ob_end() functions into ob_get_contents()

See the example below

// Create a test source image for this example
$im = imagecreatetruecolor(300, 50);
$text_color = imagecolorallocate($im, 233, 14, 91);
imagestring($im, 1, 5, 5'A Simple Text String', $text_color);

// start buffering
// output jpeg (or any other chosen) format & quality
imagejpeg($im, NULL, 85);
// capture output to string
$contents = ob_get_contents();
// end capture

// be tidy; free up memory

// lastly (for the example) we are writing the string to a file
$fh = fopen("./temp/img.jpg", "a+" );
fwrite( $fh, $contents );
fclose( $fh );


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