apparently something changed from php 5.5 to 5.6.
I used to call ImagePng($image, '');
apparently this doesn't work anymore in 5.6 as it returns: imagepng(): Filename cannot be empty
ImagePng($image, NULL);
seems to work fine though.
(PHP 4, PHP 5, PHP 7)
imagepng — 以 PNG 格式将图像输出到浏览器或文件
$image
[, string $filename
] ) : bool
imagepng() 将 GD 图像流（image）以
PNG 格式输出到标准输出（通常为浏览器），或者如果用
filename 给出了文件名则将其输出到该文件。
<?php
$im = imagecreatefrompng("test.png");
imagepng($im);
?>
apparently something changed from php 5.5 to 5.6.
I used to call ImagePng($image, '');
apparently this doesn't work anymore in 5.6 as it returns: imagepng(): Filename cannot be empty
ImagePng($image, NULL);
seems to work fine though.
I was curious about the relationship between quality, processing time and resulting image size, so I created this little benchmark to test it (The image used was originally RGB_24bits_palette_R85.png, found on wikipedia). Results are at the bottom.
<?php
$sizes = ['32', '64', '128', '256', '512', '1024', '2048'];
foreach ($sizes as $size) {
echo "\nSize: {$size}x{$size}px:\n";
$image = imagecreatefrompng("images/test{$size}.png");
for ($quality = 0; $quality < 10; $quality++) {
ob_start();
$start = microtime(true);
imagepng($image, null, $quality);
$elapsed = microtime(true) - $start;
$blob = ob_get_contents();
ob_end_clean();
$blobSize = strlen($blob);
echo "quality: $quality, size: $blobSize, elapsed: $elapsed\n";
}
imagedestroy($image);
}
// Results (some omitted for brevity):
// Size: 32x32px:
// quality: 0, size: 3172, elapsed: 0.00013399124145508
// quality: 1, size: 266, elapsed: 9.4890594482422E-5
// quality: 2, size: 264, elapsed: 7.7009201049805E-5
// quality: 3, size: 223, elapsed: 7.4863433837891E-5
// quality: 4, size: 225, elapsed: 8.5830688476562E-5
// quality: 5, size: 209, elapsed: 8.5115432739258E-5
// quality: 6, size: 208, elapsed: 9.608268737793E-5
// quality: 7, size: 205, elapsed: 0.0001060962677002
// quality: 8, size: 186, elapsed: 0.00015091896057129
// quality: 9, size: 181, elapsed: 0.00022006034851074
// Size: 128x128px:
// quality: 0, size: 49425, elapsed: 0.0010969638824463
// quality: 1, size: 976, elapsed: 0.00091886520385742
// quality: 2, size: 938, elapsed: 0.00088310241699219
// quality: 3, size: 925, elapsed: 0.00087594985961914
// quality: 4, size: 608, elapsed: 0.0009760856628418
// quality: 5, size: 607, elapsed: 0.00098395347595215
// quality: 6, size: 601, elapsed: 0.0010099411010742
// quality: 7, size: 602, elapsed: 0.001086950302124
// quality: 8, size: 521, elapsed: 0.001910924911499
// quality: 9, size: 491, elapsed: 0.0029060840606689
// Size: 512x512px:
// quality: 0, size: 788279, elapsed: 0.012928009033203
// quality: 1, size: 12467, elapsed: 0.013065099716187
// quality: 2, size: 11885, elapsed: 0.013008117675781
// quality: 3, size: 11190, elapsed: 0.013030052185059
// quality: 4, size: 7311, elapsed: 0.016619920730591
// quality: 5, size: 6994, elapsed: 0.016351222991943
// quality: 6, size: 6475, elapsed: 0.016234159469604
// quality: 7, size: 6432, elapsed: 0.016525983810425
// quality: 8, size: 6094, elapsed: 0.022937774658203
// quality: 9, size: 5649, elapsed: 0.065664052963257
// Size: 2048x2048px:
// quality: 0, size: 12605375, elapsed: 0.20983290672302
// quality: 1, size: 451735, elapsed: 0.19678711891174
// quality: 2, size: 409375, elapsed: 0.19415307044983
// quality: 3, size: 366404, elapsed: 0.20460414886475
// quality: 4, size: 312538, elapsed: 0.22785305976868
// quality: 5, size: 281671, elapsed: 0.23320484161377
// quality: 6, size: 244248, elapsed: 0.28935289382935
// quality: 7, size: 238310, elapsed: 0.33481192588806
// quality: 8, size: 217038, elapsed: 0.71698379516602
// quality: 9, size: 208881, elapsed: 1.858146905899
?>
If you are outputting a PNG directly in response to a client request it is important to check your web server configuration.
Some clients may request your images with a <a href="http://www.w3.org/Protocols/rfc2616/rfc2616-sec14.html">accept header</a> of image/*. Default configurations of Apache and possibly other servers will by default NOT allow your script to run in response to this request.
Apache is specifically discussed at http://stackoverflow.com/q/19169337 but other server have been documented to have issue too.
In other words, when testing your application don't just use the web browser, consider a phone's browser and networking libraries which could send different headers.
Be careful when using a variable for the file name.
PHP behavior with $filename differs when switching to PHP5.4 : PHP5.3 will use $filename='' the same way as $filename=NULL (e.g. no warning)
<?php
$im = imagecreatetruecolor(10,10);
imagepng($im,'',9); # Warning: imagepng(): Filename cannot be empty
imagepng($im,NULL,9); # works as expected
imagedestroy($im);
?>
The name "quality" for the compression parameter is quite misleading, as png compression is always lossless. The trade off is between speed and filesize, it cannot affect quality.
Here's something I found at stackoverflow; I haven't checked it, but if it is correct it should definitely included in the documentation:
---
from php source (gd.h):
/* 2.0.12: Compression level: 0-9 or -1, where 0 is NO COMPRESSION at all,
* 1 is FASTEST but produces larger files, 9 provides the best
* compression (smallest files) but takes a long time to compress, and
* -1 selects the default compiled into the zlib library.
*/
Conclusion: Based on the Zlib manual (http://www.zlib.net/manual.html) the default compression level is set to 6.
---
Regarding suggestions to rescale the 0-99 quality range of jpeg into the 0-9 range of png, note that for jpeg 99 is minimum compression (maximum quality) while for png 9 is maximum compression (quality doesn't change).
My script was unable to complete: Fatal error: Allowed memory size of XX bytes exhausted (tried to allocate XX+n bytes).
I found out that PHP handles images in uncompressed format: my input image was 8768x4282@32 bit => ~150 MB per single in-memory copy.
As a solution, you can either check the dimensions and reject anything too big or, as I did, use ini_set('memory_limit','1024M'); on the page start (if your server has enough on board memory).
If you care about speed, you probably already cache your generated images to a file. In that case, DON'T use "createimagefrompng" and "imagepng" to output the image. Use fpassthru instead. It is literally hundreds of times faster.
<?php
header("Content-Type: image/png");
# Generate cachefile for image, if it doesn't exist
if( !file_exists($cachefile) ) {
$im = generateimage(); # some code generates an image resource
imagepng($im, $cachefile); # store the image to cachefile
# don't output it like this:
/* imagepng($im);*/
imagedestroy($im);
}
$fp = fopen($cachefile, 'rb'); # stream the image directly from the cachefile
fpassthru($fp);
exit;
?>
I've tested it with a 5120x5120 (1.2Mb) image, that was cached on the harddisk. Using imagepng, the transfer took 12 seconds. Using fpassthru, it took only 32ms!
Creating a transparent image filled with tranparent color only
I had some hard times putting up this one:
<?php
// Set the image
$img = imagecreatetruecolor(100,100);
imagesavealpha($img, true);
// Fill the image with transparent color
$color = imagecolorallocatealpha($img,0x00,0x00,0x00,127);
imagefill($img, 0, 0, $color);
// Save the image to file.png
imagepng($img, "file.png");
// Destroy image
imagedestroy($img);
?>
If you're generating an image dynamically based on post data and don't want to save it to the server, sending it to be displayed can cause problems as when the person tries to save it, the browser will request it again from the server (causing any post data to be lost and probably a corrupted png).
The easiest way to get around this is to force it to download using the content disposition header, for example:
<?php
header('Content-Disposition: Attachment;filename=image.png');
header('Content-type: image/png');
?>
If you need to call imagepng() multiple times (for example, when you want to send it to the browser, but also to a disk cache), write your image to a file first, THEN call readfile() on it.
PHP internally works with a temporary file when sending the image to the browser, so you'll gain nothing by calling imagepng() twice.
When you allow multiple output formats, (jpg/png) but want to use the 1-100 quality scale (like jpg), you will have to format the number:
<?php
$pngQuality = ($quality - 100) / 11.111111;
$pngQuality = round(abs($pngQuality));
imagepng($resource, $path, $pngQuality);
?>
I just lost about 4 hours on a really stupid problem. My images on the local server were somehow broken and therefore did not display in the browsers. After much looking around and testing, including re-installing apache on my computer a couple of times, I traced the problem to an included file.
No the problem was not a whitespace, but the UTF BOM encoding character at the begining of one of my inluded files...
So beware of your included files!
Make sure they are not encoded in UTF or otherwise in UTF without BOM.
Hope it save someone's time.
I ran across the following WRT sessions and image creation.
In main.php:
<?php
(...session in progress...)
$_SESSION['text']='some text...';
$imgSrc='http://foo.com/createImage.php?sid='.session_id();
echo('<img src="'.$imgSrc.'"/>');
unset($_SESSION['text']);
...
?>
In createImage.php:
<?php
header('image/png');
session_id($_REQUEST['sid']);
session_start();
$img=imagecreatetruecolor(200, 30);
$text_color=imagecolorallocate($img, 200, 200, 200);
imagestring($img, 5, 5, 5, $_SESSION['text'], $text_color);
imagepng($img);
imagedestroy($img);
?>
Problem: main.php execution ends before createImage.php writing the text to image, thus the unset($_SESSION['text']) destroys the text and you end up with empty image.
Solution: move call to unset() as last statement of createImage.php
To change the background of a 24-bit PNG for graceful degradation in IE6, the PNG file needs a bKGD chunk:
<?php
// insert a BKGD chunk into the PNG file for graceful image degradation in IE6
$bgColor = array(250, 250, 250);
$pngData = bin2hex(file_get_contents($filename));
$idatMarker = '200049444154';
$bkgdMarker = '624b4744';
$bkgdChunk = '0006' . $bkgdMarker;
foreach ($bgColor as $bit)
{
$bkgdChunkData .= '00' . dechex($bit);
}
$bkgdChunk .= $bkgdChunkData;
$bkgdChunk .= dechex(crc32(pack('H*', $bkgdMarker . $bkgdChunkData))) . '0000';
$parsed = explode($idatMarker, $pngData, 2); // split file by first 'IDAT' chunk
$pngData = pack('H*', $parsed[0] . $bkgdChunk . $idatMarker . $parsed[1]);
file_put_contents($cachedFilename, $pngData);
?>
<?php
// aid of the highlighted Alliance
$marked_aid = 2403;
// Preferences
$mysqlhost = 'localhost';
$mysqluser = 'user';
$mysqlpass = 'password';
$mysqldb = 'database';
// Create database connection and select database
$db = @mysql_connect($mysqlhost, $mysqluser, $mysqlpass) OR die('Can not connect to DB-Server!');
$db_select = @mysql_select_db($mysqldb) OR die('Can not select DB!');
// Create image: Map goes from -400 to 400
// -> sums up tp 2*400+1 (+1 due to the 0 in the center)
$image = imagecreate(801, 801);
// Choose the colors of background, normal village and highlighted alliance
$color_background = imagecolorallocate($image, 255, 255, 255);
$color_normal = imagecolorallocate($image, 200, 200, 200);
$color_marked = imagecolorallocate($image, 255, 0, 0);
// Fill images background with chosen color
imagefill($image, 0, 0, $color_background);
// Select ALL villages from the DB and order by ascending ID
// (Fields are numbered from top left to bottom right)
$query = 'SELECT x, y, aid FROM x_world ORDER BY id ASC';
$result = @mysql_query($query) OR die('Can not select villages from table x_world!');
// Check whether there any villages at all
if (mysql_num_rows($result)) {
// Select first village
$row = @mysql_fetch_assoc($result);
// These variables save the location on which we are currently drawing
$x_pointer = 0;
$y_pointer = 0;
// Outer loop for the Y-coordinates
for($y=400; $y >= -400; $y--) {
// Inner loop for the X-coordinates
for ($x=-400; $x <= 400; $x++) {
// Once we reached the coordinates matching the current record selected from the DB:
if ($row['x'] == $x AND $row['y'] == $y) {
// Selecting the village color depending on the aid
if ($row['aid'] == $marked_aid) {
$color = $color_marked;
} else {
$color = $color_normal;
}
// Drawing the village with the selected color
imagefilledrectangle($image, $x_pointer, $y_pointer, ($x_pointer + 1), ($y_pointer + 1), $color);
// Select next record
$row = @mysql_fetch_assoc($result);
}
// Increase pointer for X-coordinate
$x_pointer++;
}
// Increase pointer for Y-coordinate
$y_pointer++;
// We reached the end of a line and have to set the X-pointer to 0 again
$x_pointer = 0;
}
}
// Select the HTTP-Header for the selected filetype
header("Content-Type: image/png");
// Generate image and print it
imagepng($image);
?>
If you want to open a png image with alpha blending, you need to do something like this:
<?php
$file = 'semitransparent.png'; // path to png image
$img = imagecreatefrompng($file); // open image
imagealphablending($img, true); // setting alpha blending on
imagesavealpha($img, true); // save alphablending setting (important)
?>
I spent almost a day to find out why alpha blending doesn't work. I hope this is usefull to others too :)
@ phpman at texmedia dot de:
The compression range in PNG is in range 0-9, i think if you specified a compression level higher than 9, it'll be completely "compressed", or suppressed in the other words.
The compression level is originally for JPEG, which is in range 0 - 100, I think it'll work fine if you divide it by ten before passing to imagepng(). ;)
My webserver, running 5.14 didn't like the header that was generated using imagepng(). It works find on my local test server and on 4.x from another host.
The generated image displays in the browser (IE, firefox) but when saved to a file or inserted into an RTF file, the image was corrupted. As a test, when attempting to right-click to save as, the image format was not recognized.
The only work-around appears to be adding the additional paramaters.
So instead of just
imagepng($image); //DIDNT WORK--CORUPT IMAGE
This worked
imagepng($image,NULL,0,NULL);
and saving to disk, this worked:
imagepng($image,$file_location,0,NULL);
Jeff
When changeing the PHP version from 4 to 5 I found out, that PHP5 handles imagepng() more restrictive than in PHP4. I'd used
imagepng($image,'',90);
to reduce the image quality whithout saving the image as a file. The quality parameter is not supported at all, I used imagejpg before and simply changed the function to imagepng whithout taking care of the existing parameters. It did not matter and there was no error in PHP4. But in PHP5, the image will not be shown anymore. So you have to remove it to have the standard:
imagepng($image);
barts code below does not work at least with gd 2
Only returns a blank image with alpha not the source resized
$im = ImageCreateFromPNG($sourcefile);
$im_dest = imagecreatetruecolor ($forcedwidth, $forcedheight);
imagealphablending($im_dest, false);
imagecopyresampled($im_dest, $im, 0, 0, 0, 0, $wm_width, $wm_height, $forcedwidth, $forcedheight);
imagesavealpha($im_dest, true);
imagepng($im_dest, $destfile);
imagedestroy($img_dest);
ps you also forgot image destroy and you had a random var in imagepng undefined in your post
If you want to resize a png-24 image and preserve the alpha channel you need to set imagealphablending($im_dest, false) on the destination image just after creating it with imagecreatetruecolor() and do a imagesavealpha($im_dest, true) on it before saving it:
<?php
$im = ImageCreateFromPNG('redfade.png');
$im_dest = imagecreatetruecolor (500, 300);
imagealphablending($im_dest, false);
imagecopyresampled($im_dest, $im, 0, 0, 0, 0, 300, 300, 500, 300);
imagesavealpha($im_dest, true);
imagepng($im_re, 'small_redfade.png');
?>
Trying to resize a png 256 colors image and save it in 256 colors with a correct color palette ? (if you'll save a 256 color image in truecolor palette the result image will have a big size).
I spent some hours trying various function to get a good quality 256 color png image, but because of color palette the result image quality was awful.
But thank to the comment of zmorris at zsculpt dot com from imagetruecolortopalette function page, i figured out how to get a properly image!
<?php
function resize_png($src,$dst,$dstw,$dsth) {
list($width, $height, $type, $attr) = getimagesize($src);
$im = imagecreatefrompng($src);
$tim = imagecreatetruecolor($dstw,$dsth);
imagecopyresampled($tim,$im,0,0,0,0,$dstw,$dsth,$width,$height);
$tim = ImageTrueColorToPalette2($tim,false,255);
imagepng($tim,$dst);
}
//zmorris at zsculpt dot com function, a bit completed
function ImageTrueColorToPalette2($image, $dither, $ncolors) {
$width = imagesx( $image );
$height = imagesy( $image );
$colors_handle = ImageCreateTrueColor( $width, $height );
ImageCopyMerge( $colors_handle, $image, 0, 0, 0, 0, $width, $height, 100 );
ImageTrueColorToPalette( $image, $dither, $ncolors );
ImageColorMatch( $colors_handle, $image );
ImageDestroy($colors_handle);
return $image;
}
?>
Good luck,
Namolovan Nicolae, Moldova
PNG images (as any image) can be stored in a MySQL blob field, but if you want to do this, you'll want to serialize the image stream into a better form. I would recommend base64_encode() and base64_decode(). (Just fopen() the file, fread() the contents in, base64_encode() the string, and fire off your SQL query (use addslashes()/stripslashes() to be more secure)).
This has been posted an innumerable amount of times throughout the site, but it's still terrible that a lot of users simply don't understand this and use it to its full potential.
I would also recommend that if you are doing images this way, to keep an image cache folder somewhere that PHP can access (possibly even somewhere off your webroot?). That way if your website is swamped with traffic it won't kill the SQL server.
To send 'Content-Length' header (like in static pictures case) i use "Output handler" like this...
<?php
// Output handler
function output_handler($img) {
header('Content-type: image/png');
header('Content-Length: ' . strlen($img));
return $img;
}
// Image output
ob_start("output_handler");
imagepng($im);
ob_end_flush();
?>
This is my way to store PNG-images in a MySQL database... You cannot directly store the PNG-image in a variable, and then parse it in the database, cos if you try to define it to a variable, it'll still just output it...
In my method i use three functions
to "capture" the output and store it in a variable; ob_start (to start the output buffering), ob_get_contents (to capture the output), and ob_end_clean (to erase the cache, and end the output buffering)
<?php
$imagefile = "changethistogourimage.gif";
$image = imagecreatefromgif($imagefile);
ob_start();
imagepng($image);
$imagevariable = ob_get_contents();
ob_end_clean();
/*
HERE YOU CAN MESS WITH THE $imagevariable AS YOU LIKE
*/
?>
You could use the function imagecreatefrompng
(I assume that you already know how to get the text from the url.)
The only thing left to do is put that text on the image using the correct colors for you.
<?php
$im = @imagecreatefrompng($imgname);
$text_color = imagecolorallocate ($im, $Red,$Green,$Blue);
imagestring ($im, 3, 5, 15, $SomeTextFromURL, $text_color);
?>
Regards,
Peter Berkhout.
Presumably it returns true on success and false on failure, although the documentation doesn't actually say so.
in reply to: cbrasho at yahoo dot com
if you use Apache as a webserver, you could do the following:
You could set up a 'img' directory in your webspace.
In that directory there will be two files: a .htaccess file and a img.php file
the .htaccess file contains the following code:
ErrorDocument 404 /img/img.php
the img.php file looks something like this:
<?php
$file = $_SERVER['REDIRECT_URL'];
$result = mysql_query('select img_blob from images where filename=\\'' . $file . '\\');
list($blob) = mysql_fetch_row($result);
header('HTTP/1.0 200 Ok');
header("Content-type: image/jpeg");
print $blob; # or whatever works, I don't use this
?>
if you use a url for your image like http://test.com/img/image1.jpeg, which doesn't exist, normally you would get a 404-page. in this case, the 404 is being handled by img.php, which brings up the required image...
Having your pictures stored in a database sounds great but brings you a lot of trouble.
Storing images in a DB you will have a script show.php that will appear in <img> tags: <img src='show.php?img_id=$some_id'>
But if you want to have REGISTER GLOBALS = OFF, you are in trouble and there is no way (at leas as far as i know) to solve the problem but to put te img from the DB in a file and put the coresponding file name in the <img> tag. But this brings another problem: simultaneous accesses to the page. So you will have to find a way to give unique names to the picture files for each simultaneous access to the page. The solution might be using sessions. This is how you end up having a very compleh PHP script for a very simple problem. So, the basic ideea is " do not store your pictures in a blob unless you know exactly what you are doing".
to all the ones, who like having their users fill their profil with an image without destroying a fixed design the following should be a great way to handle this problem.
this file opens a picture from $imagepath and returns it as a valid picture to embed in: <img src="file.php?image=123.jpg[?maxX=200&maxY=150]"> (in [] = optional)
but this file does more than this. it also adds black borders to files that are smaller than the max. size, so adding borders to the left and right where a image is too high :-)
if there is a need for a copyright note this script will also help you. you can put in a various text to $copyright. the text length should be in relationship to $maxX and $maxY.
Well there are other features of the script, just try'em out and have fun with it :-)
bye
<?php
# standard height & weight if not given
if(!isset($maxX)) $maxX = 100;
if(!isset($maxY)) $maxY = 75;
# colour- & textvalues
$picBG = "0,0,0"; # RGB-value !
$picFG = "104,104,104"; # RGB-value !
$copyright = "stefan bechtold";
$font = 1;
# minimal & maximum zoom
$minZoom = 1; # per cent related on orginal (!=0)
$maxZoom = 200; # per cent related on orginal (!=0)
# paths
$imgpath = "userimages/"; # ending with "/" !
$nopicurl = "../images/nopic.jpg"; # starting in $imagepath!!!
$nofileurl = "../images/nofile.jpg"; # starting in $imagepath!!!
if(!isset($image) || empty($image))
$imageurl = $imgpath . $nopicurl;
elseif(! file_exists($imgpath . trim($image)))
$imageurl = $imgpath . $nofileurl;
else
$imageurl = $imgpath . trim($image);
# reading image
$image = getImageSize($imageurl, $info); # $info, only to handle problems with earlier php versions...
switch($image[2]) {
case 1:
# GIF image
$timg = imageCreateFromGIF($imageurl);
break;
case 2:
# JPEG image
$timg = imageCreateFromJPEG($imageurl);
break;
case 3:
# PNG image
$timg = imageCreateFromPNG($imageurl);
break;
}
# reading image sizes
$imgX = $image[0];
$imgY = $image[1];
# calculation zoom factor
$_X = $imgX/$maxX * 100;
$_Y = $imgY/$maxY * 100;
# selecting correct zoom factor, so that the image always keeps in the given format
# no matter if it is more higher than wider or the other way around
if((100-$_X) < (100-$_Y)) $_K = $_X;
else $_K = $_Y;
# zoom check to the original
if($_K > 10000/$minZoom) $_K = 10000/$minZoom;
if($_K < 10000/$maxZoom) $_K = 10000/$maxZoom;
# calculate new image sizes
$newX = $imgX/$_K * 100;
$newY = $imgY/$_K * 100;
# set start positoin of the image
# always centered
$posX = ($maxX-$newX) / 2;
$posY = ($maxY-$newY) / 2;
# creating new image with given sizes
$imgh = imageCreateTrueColor($maxX, $maxY);
# setting colours
$cols = explode(",", $picBG);
$bgcol = imageColorallocate($imgh, trim($cols[0]), trim($cols[1]), trim($cols[2]));
$cols = explode(",", $picFG);
$fgcol = imageColorallocate($imgh, trim($cols[0]), trim($cols[1]), trim($cols[2]));
# fill background
imageFill($imgh, 0, 0, $bgcol);
# create small copy of the image
imageCopyResampled($imgh, $timg, $posX, $posY, 0, 0, $newX, $newY, $image[0], $image[1]);
# writing copyright note
imageStringUp($imgh, $font, $maxX-9, $maxY-3, $copyright, $fgcol);
# output
switch($image[2]) {
case 1:
# GIF image
header("Content-type: image/gif");
imageGIF($imgh);
case 2:
# JPEG image
header("Content-type: image/jpeg");
imageJPEG($imgh);
case 3:
# PNG image
header("Content-type: image/png");
imagePNG($imgh);
}
# cleaning cache
imageDestroy($timg);
imageDestroy($imgh);
?>
"Tip: As with anything that outputs its result directly to the browser, you can use the output-control functions (http://www.php.net/manual/en/ref.outcontrol.php) to capture the output of this function, and save it in a string (for example)."
ob_start();
imagepng($image);
$image_data = ob_get_contents();
ob_end_clean();
And now you can save $image_data to a database, for example, instead of first writing it to file and then reading the data from it. Just don't forget to use mysql_escape_string...
PNG files are already compressed. They use a lossless compression algorithm. If you are using HighColour images, the compression only does so much. For low colour images (16 or 256) the compression is much better.
It is pointless trying to compress the images further before sending to a browser.
I have experienced segfaults and bus errors with the following configuration: FreeBSD4.4, Apache 1.3.26, PHP 4.2.2, GD-1.8.4, PDFlib 4.0.1. The apache process crashed when calling the imagepng function, but it didn't crash when calling the imagejpg function, or imagecreatefrompng...
Some wasted hours (lots) later, in which I have tried to recompile gd, libpng, php, libjpeg, what-not, I have found the following advices:
http://bugs.php.net/bug.php?id=16841
So the problem was not with the png library, but rather with the PDFlib. Even though all the threads led to a png-problem... so I have simply upgraded to PDFlib 4.0.3 (w/o any special configure arguments; --with-libpng didn't work anyways), recompiled PHP, and now everything works (imagepng, pdf creation, etc.).
Hope this helps,
bogdan
Better than a chmod 777 to any '/dir/pic.png' you should :
- test if dir is writable (is_writable func.)
- use chmod 700 (more secure because let only the webserver ID have access)
In any case you should program a (crontab) script to change the owner ID of any images created.