I'm experiencing the same issue as Soma, except my images are JPG. In my generated thumbnails from my master images, the white becomes off-white.
I also tried modifying config's imageSizerOptions, however this didn't fix the issue:
$config->imageSizerOptions = array(
//"forceNew" => true,
'upscaling' => true, // upscale if necessary to reach target size?
'cropping' => true, // crop if necessary to reach target size?
'autoRotation' => true, // automatically correct orientation?
// changed from soft
'sharpening' => 'none', // sharpening: none | soft | medium | strong
// changed from 90
'quality' => 100, // quality: 1-100 where higher is better but bigger
// changed from 60
'hidpiQuality' => 100, // Same as above quality setting, but specific to hidpi images
// changed from 2.0
'defaultGamma' => -1, // defaultGamma: 0.5 to 4.0 or -1 to disable gamma correction (default=2.0)
);
One thing I also tried was to mess with the original image's color profiles and such in Photoshop and then regenerated new thumbnails based off of that, but that didn't work either.
I have a suspicion that this has to do with WAMP's image processor?