poor-quality thumbnails

[Melville]

I am making thumbnails out of .jpg files, and some of them are of really poor quality. Some may come out in black and white. Some may be milky. Some may be blurry. Some may look like negatives (i.e., very dark). Many look just fine. I have checked the full-size photos of many of the poor-quality thumbnails, and the full-size photos appear fine.

Does anyone know of a way to address this problem?

Here is the code I am using:

function createthumb($name,$filename,$new_w){
// These lines get the information if gd is at least version 2.0 and check if the original image is a JPEG or PNG
// and a new image object is created called src_image
global $gd2;
$system=explode(".",$name);
if (preg_match("/jpg|jpeg/",$system[1])){
$src_img = @imagecreatefromjpeg($name); / Attempt to open /
if (!$src_img) { / See if it failed /
}
}

// These lines get the dimensions of the original image by using imageSX() and imageSY(), 
// and calculate the dimensions of the thumbnail accordingly, keeping the correct aspect ratio. 
// The desired dimensions are stored in thumb_w and thumb_h.
$old_x=imageSX($src_img); 
$old_y=imageSY($src_img); 
$thumb_w=$new_w;
$thumb_h=$old_y/$old_x * $new_w;

//These lines check the version of gd (coming from checkgd()) and create the image either as a 256 colour version using ImageCreate()
// or as a true colour version using ImageCreateTrueColor().
if ($gd2==""){ 
    $dst_img=ImageCreate($thumb_w,$thumb_h); 
    imagecopyresized($dst_img,$src_img,0,0,0,0,$thumb_w,$thumb_h,$old_x,$old_y); 
}else{ 
    $dst_img=ImageCreateTrueColor($thumb_w,$thumb_h); 
    imagecopyresampled($dst_img,$src_img,0,0,0,0,$thumb_w,$thumb_h,$old_x,$old_y); 
} 

// Then the original image gets resized, respectively resampled and copied into the new thumbnail image, on the top left position
if (preg_match("/png/",$system[1])){ 
    imagepng($dst_img,$filename); 
} else { 
    imagejpeg($dst_img,$filename); 
} 
imagedestroy($dst_img); 
imagedestroy($src_img); 

}

Thank you for any assistance you may provide!

Mel

[jpmoriarty]

i cant see where you define what $gd2 is - so i think it's always using imagecopy instead of the full colour one.

[Melville]

Thank you, John. I was assuming that $gd2 is defined in the gd library that is installed with PHP4+. Is that not the case?

I just ran a simple test to see if $gd2 had a value, and it does not.

Is there an include file I need? Or is there something specific I should set or test?

Thank you,

Mel

[jpmoriarty]

have a look at gd_info() . In particular the user notes:

For my image gallery script I need to know if the GD version is 1.x or >=2 because I want to use TrueColor-capable functions if available, otherwise have the script fall back to the HiColor versions. To that end, I wrote a function that grabs just the major version number of the installed GD extension. This function works on versions of PHP older than 4.3.

/**
* Get which version of GD is installed, if any.
*
* Returns the version (1 or 2) of the GD extension.
*/
function gdVersion() {
   if (! extension_loaded('gd')) { return; }
   ob_start();
   phpinfo(8);
   $info=ob_get_contents();
   ob_end_clean();
   $info=stristr($info, 'gd version');
   preg_match('/\d/', $info, $gd);
   return $gd[0];
} // end function gdVersion()

// The function is easy to use.

if ($gdv = gdVersion()) {
  if ($gdv >=2) {
   echo 'imageCreateTruecolor() and imageCopyResampled() functions may be used.';
  } else {
   echo 'imageCreate() and imageCopyResized() functions must be used.';
  }
} else {
  echo "The GD extension isn't loaded.";
} 

Always a good idea to search the manual first - in this case i searched for "gd" and gd_info was the first thing to come up...

[Melville]

Thank you again, John. I did search the manual right after I posted the last reply. I will do that in the future before posting anything. I also found something that I am about to try. It is:

function gd_version() {
static $gd_version_number = null;
if ($gd_version_number === null) {
// Use output buffering to get results from phpinfo()
// without disturbing the page we're in. Output
// buffering is "stackable" so we don't even have to
// worry about previous or encompassing buffering.
ob_start();
phpinfo(8);
$module_info = ob_get_contents();
ob_end_clean();
if (preg_match("/\bgd\s+version\b[^{\d\n\r]+?([\d.]+)/i",}
$module_info,$matches)) {
$gd_version_number = $matches[1];
} else {
$gd_version_number = 0;
}
}
return $gd_version_number;
}

Unfortunately, it never occurred to me to test $gd2 in my code. I simply made a bad assumption. But I am on the right track now, thanks to you.

Best,

Mel

[phamweb]

pre-defined dimension resize wouldn't do?

$size = GetImageSize("../images/".$product["product_ID"].".jpg");
if($size[0]>0 && $size[1]>0)
echo "<td><img src=\"../images/".$product["product_ID"].".jpg\" border=0 width = ". $size[0] ." height = " .$size[1]

[Melville]

This looks like it would work. I did find that my last attempt worked well (see above). Thank you very much for your solution!