gifload: no property named dpi

[ethaniel]

Hello and thank you for the amazing binding.

I am trying to make a "universal" loader which accepts all kinds of images, but for example I would like to set those that have a property named dpi to a value of 300.

If I add an option called dpi to the Vips\Image::newFromFile options, and I am loading a normal gif image, I get a gifload: no property named dpi error.

I already use Vips\Image::findLoad to detect the kind of image I'm loading before I set the options. But I was wondering if it's possible to check if a dpi option exists for a specific loader (so I wouldn't have to hardcode the option exceptions for gif/jpg/etc)?

[jcupitt]

Hi, it's not too well documented, but you can use Introspect to find the arguments for operations:

https://libvips.github.io/php-vips/classes/Jcupitt-Vips-Introspect.html

The source might be helpful:

https://github.com/libvips/php-vips/blob/master/src/Introspect.php

It's used here (might help too):

https://github.com/libvips/php-vips/blob/master/src/Introspect.php

[jcupitt]

Are you trying to detect things like memory bombs? You can do this after opening, something like:

$image = Vips\Image::newFromFile($filename);
if ($image->width * $image->height * $image->bands > $size_threshold) {
    error("image too big!!");
}

newFromFile will read the image metadata, but won't do any decoding (that happens the first time you read pixel values), so it can't trigger out of memory.

[ethaniel]

In some cases, my users upload PDFs or TIFFs. I want these files to be loaded with a dpi of 300. So I want to know beforehand, if I should apply the dpi option to the loader or not. Thank you for the Introspect, I will look into it.

[jcupitt]

Ah OK. I would sniff the type and then have a special path for pdf, eg. (untested):

$loader = Vips\Image::findLoad($filename);
if ($loader == "VipsForeignLoadPdfFile") {
    $image = Vips/Image::newFromFile($filename, ["dpi" => 300]);
}
else {
    $image = Vips/Image::newFromFile($filename);
}