polaroidImage and transparent formats

[tk1]

Hi!

I'm writing PHP functions with Imagick to make some effects on the webpages. I use polaroidImage function but when non transparent images are posted I see black border. I would like to have transparent background.

How can I detect if image supports transparency and then save as f.e. PNG ?

[snibgo]

... but when non transparent images are posted ...

I don't think that is what you mean.

It might help if you posted your code and sample inputs/outputs.

To ensure an image has no transparency, "-alpha off" is the command-line option.

[tk1]

[code]
try {
$newIm = new \Imagick();
$newIm->setBackgroundColor(new \ImagickPixel('transparent'));
$newIm->readImage($file);

$geo = $newIm->getImageGeometry();
$newIm->polaroidImage(new \ImagickDraw(), $value); // IM >= 6.3.2
$newIm->resizeImage($geo['width'], $geo['height'], $this->gfxConf['windowing_filter'], 1);

$newIm->writeImage($file);
$newIm->destroy();

return TRUE;
}
catch(ImagickException $e) {
[/code]

I would like to add transparency detection and change output image format if prestnt format doesn't support transparency. Now with JPG's I have black background.

[fmw42]

JPG does not support transparency. Use PNG or TIFF.

[tk1]

Yes. Jpeg doesn't support transparency. Users may use my function on various image formats.
This is why I would like to change output image format. But, how to enrich my function in image transparency detection?
I think image extension or format is not enough.

[fmw42]

I do not know how you would do this in your API, but see string formats %A and %[channels] to detect transparency at http://www.imagemagick.org/script/escape.php