UNSOLVED: Dynamically changing colors and resizing image

[techno_race]

Well, here's my problem. I have a GIF image that has black and white.
I need to be able to use $_GET['black'] and $_GET['white'] (or something like that) to get two user-submitted hex triplets (with leading #).
Then replace all black in the image with $_GET['black'] and all white with $_GET['white'].
Then I have to resize the image to predefined (larger) dimensions using a bicubic method (as to create a gradient).
Finally, I have to send the finished image to the user as a GIF.
Then I have to repeat the process for multiple users (at once?).

I know I'll probably have to install some sort of image library, like ImageMagick or GD.
I don't know how to do this. I have very little experience with PHP, let alone PHP extensions.
Is there any way to do this on a remote server? If so, how? If not, now what?

[james438]

Do you have GD or Imagemagik? What I mean is are you sure you do not have these? I have recently started learning about php's ability to process images. It is interesting and rather fun.

To see if you have GD try running this snippet of code:

<pre><?php
var_dump(gd_info());
?></pre>

Other than that all I really know how to do thus far is use php to generate a high quality thumbnail that loads really fast without creating a new image file and use php to create a file that is a thumbnail version of an image which is also in really high quality depending on whether you want to create a new image file or just view what it would like to help decide the format of the file to be created.

Are you saying that $_GET['black'] could be any color depending on what the user submits?

[techno_race]

It turns out I have GD...I think...

array(12) { ["GD Version"]=> string(27) "bundled (2.0.34 compatible)" ["FreeType Support"]=> bool(true) ["FreeType Linkage"]=> string(13) "with freetype" ["T1Lib Support"]=> bool(false) ["GIF Read Support"]=> bool(true) ["GIF Create Support"]=> bool(true) ["JPG Support"]=> bool(true) ["PNG Support"]=> bool(true) ["WBMP Support"]=> bool(true) ["XPM Support"]=> bool(true) ["XBM Support"]=> bool(true) ["JIS-mapped Japanese Font Support"]=> bool(false) }

And I think the hosting feature list mentioned ImageMagick...
:moreconfused:

Are you saying that $_GET['black'] could be any color depending on what the user submits?

Yes, any hex triplet.

So, the user goes to, say, image.php?black=#09F673&white=#9FD33E
I have a predefined image, say, image.gif
It replaces all #000000 in image.gif with #09F673
It replaces all #FFFFFF in image.gif with #9FD33E
It saves the file as, say, image0548394748.gif (PIN)
It bicubically (?) resizes image0548394748.gif to predefined dimensions, preferably using variables, as I have to do this for different images at different sizes.
It resaves image0548394748.gif
It gives image0548394748.gif to the user
After, say, 5 minutes, it deletes image0548394748.gif
It repeats this for diferent users, possibly simultaneously.

[techno_race]

I have GD 2.0.34, but not ImageMagick.

[james438]

Hi,

Still working on it. I have only very very recently started looking at the GD functions of PHP, so my skills are certainly lacking. However here are a few scripts I have discovered.

Resizes the image and outputs it directly to a web browser witout saving the file anywhere.

<?php
// The file
$filename = 'images/picture.jpg';
$percent = 0.25;

// Content type
header('Content-type: image/jpeg');

// Get new dimensions
list($width, $height) = getimagesize($filename);
$new_width = $width * $percent;
$new_height = $height * $percent;

// Resample
$image_p = imagecreatetruecolor($new_width, $new_height);
$image = imagecreatefromjpeg($filename);
imagecopyresampled($image_p, $image, 0, 0, 0, 0, $new_width, $new_height, $width, $height);

// Output
imagejpeg($image_p, null, 100);
?>

Add the following at the end of the script to save the resized image to a file on your server. The original file is not destroyed.

$dest="try1.jpg";
imagepng($image_p,$dest); 

There are a great deal of terms that I am still unfamiliar with, but the following will replace one color with another in a created image. This is not exactly what we want, but at least we are getting closer. It can be applied to an image, but I do not know how to do that yet.

<?php
header("Content-type: image/png");
$im = imagecreate(200, 200);
$red = imagecolorallocate($im, 255, 0, 0);
$offblue = imagecolorallocate($im, 90, 90, 200);
imagefill($im, 0, 0, $red);
imagefilledrectangle($im, 10, 10, 40, 40, $offblue);
// above could come from an uploaded image
// find a blue in the image
$newblue = imagecolorclosest($im, 0, 0, 255);
// change it to green
imagecolorset($im, $newblue, 0, 255, 0);
imagepng($im);
imagedestroy($im);
?php>

I got the above code from http://www.phpdig.net/ref/rn25re393.html

[james438]

frustrating, because I can't get this or anything to work on any image I try to manipulate. I have tried converting the image to grayscale and then replacing the black, I have tried a loop to replace a range of colors, I have tried imagecolorset, imagecolorallocate, and just can't get anything to work. I can resize the image, mess with the tint, and mess with the image as a whole to invert the colors using imagecolorfilter, but I can't change one color to another.

hmmm...

P.S. I did find this article to read for later: http://www.dushu.de/englishbook/sams...7lev1sec3.html

[techno_race]

So, here's what's left:
- Generating a PIN (text file containing number that updates automatically?)
- changing the colors.

[techno_race]

When resizing the image, is it bicubic, bilinear, or neighbor?

[james438]

So, here's what's left:
- Generating a PIN (text file containing number that updates automatically?)
- changing the colors.

I don't know too much about PINs. I never had the need for them, but why not store the PIN in the database using MySQL and store the time that it was generated and have it auto-update based on the time it was submitted. For example exactly 10 minutes after the PIN is generated the PIN will reset.

Yeah, changing colors is a bugger. Remember I have only started looking at GD for the first time 2 or 3 days ago. Can you restate how you want it to change the colors, because If I were to change one color in a b&w image to another color the color would indeed change, but since there are so many different shades of gray only a few pixels in the image would change.

When resizing the image, is it bicubic, bilinear, or neighbor?

Kinda hard to find the info on that one. I went to php.net and the best I could find was that it was not known which algorithm PHP's GD uses. I am not the best judge of image quality, but I found the quality to be quite good. I hear photoshop is better though.

If you can figure out the color change problem before me please post the answer here. I am eager to see how it is done! You probably already know this, but the image processing capabilities of GD is quite processor heavy.

[techno_race]

I have an extremely small image.
One pixel is black, the other one is white.
I need to change black to x and white to y.
The user submits the new colors.
What about (for the PIN) something like:
YYYYMMDDMinuteSecondMillisecond
It would be a freak coincidence if those were exactly the same.
Why don't we just do:

<?php
header("Content-type: image/png");
$im = imagecreate(200, 200);
$red = imagecolorallocate($im, 255, 0, 0);
$offblue = imagecolorallocate($im, 90, 90, 200);
imagefill($im, 0, 0, $red);
imagefilledrectangle($im, 10, 10, 40, 40, $offblue);
// above could come from an uploaded image
// find a blue in the image
$newblue = imagecolorclosest($im, 0, 0, 255);
// change it to green
imagecolorset($im, $newblue, 0, 255, 0);
imagepng($im);
imagedestroy($im);
?php>

twice, once for each color?