When Resizing Grayscale PNG White lines appear - php

Question

When resizing some png images they appear stretched and have what looks like vertical interlacing. I'm unsure of where the issue could be, however I'm starting to think its because the image starts in grayscale and needs to have a different color profile.
Any help or suggestions would be greatly appreciated.
Original image
Image showing the problem
function createImageSize($sourcefile, $setNewName, $maxwidth, $maxheight, $quality){
$fileInfoArray = #getimagesize($sourcefile);
$imagetype = $fileInfoArray['mime'];
list($width, $height, $attr) = getimagesize($sourcefile);
switch($imagetype){
case 'image/jpeg':
$img = imagecreatefromjpeg($sourcefile);
break;
case 'image/gif':
$img = imagecreatefromgif($sourcefile);
break;
case 'image/png':
$img = imagecreatefrompng($sourcefile);
break;
case 'image/x-png':
$img = imagecreatefrompng($sourcefile);
break;
}
if ($width > $maxwidth || $height > $maxheight){
if ( $width > $height ){
$newwidth = $maxwidth;
$ratio = $maxwidth / $width;
$newheight = floor($height * $ratio);
if ($newheight > $maxheight){
$newheight = $maxheight;
$ratio = $maxheight / $height;
$newwidth = floor($width * $ratio);
}
}else{
$newheight = $maxheight;
$ratio = $maxheight / $height;
$newwidth = floor($width * $ratio);
if ($newwidth > $maxwidth){
$newwidth = $maxwidth;
$ratio = $maxwidth / $width;
$newheight = floor($height * $ratio);
}
}
}else{
$newwidth = $width;
$newheight = $height;
}
$tmpimg = imagecreatetruecolor( $newwidth, $newheight );
if($imagetype == 'image/png'||$imagetype == 'image/x-png'){
imagealphablending($tmpimg, false);
imagesavealpha($tmpimg, true);
if($imagetype == 'image/gif'){
$transparent = imagecolorallocatealpha($tmpimg, 0, 0, 0, 127);
imagecolortransparent($tmpimg, $transparent);
}
imagefilledrectangle($tmpimg, 0, 0, $newwidth, $newheight, $transparent);
}
imagecopyresampled( $tmpimg, $img, 0, 0, 0, 0, $newwidth, $newheight, $width, $height );
switch($imagetype){
case 'image/jpeg':
imagejpeg($tmpimg, $setNewName, $quality);
break;
case 'image/gif':
imagegif($tmpimg, $setNewName);
break;
case 'image/png':
imagepng($tmpimg, $setNewName, 3);
break;
case 'image/x-png':
imagepng($tmpimg, $setNewName, 3);
break;
}
imagedestroy($tmpimg);
imagedestroy($img);
}

Answer 1

I had the same problem. While generating EPS files into transparent PNG files (to use as mask images later), iMagick created the PNG files as grayscale. When GD reads grayscale PNGs, it doubles them horizontally with vertical lines in them.
My solution was handled on the iMagic side, by forcing it to write the PNGs as RGBA:
before:
$image->setImageFileName("image.png");
After:
$image->setImageFileName("png32:image.png");
I don't know where your grayscale PNGs are coming from, but if you are generating them, make sure they are created RGBA. Otherwise perhaps there is a way to read them with GD properly, specifying grayscale source.

Answer 2

I have the same issue and still haven't found any solutions. It would seem that GD doesn't like grayscale PNG8 images and is interpreting as colored.
I may have to convert the image back to 24 bits using "convert" with exec() and then delete the image, but it's far from optimal.