January, 31, 2024 archives
Enabling GD’s JPEG support in Docker for PHP 8.3
I am generating a ThumbHash for each photo in my new photo library using this PHP library, and it needs to use either the GD Graphics Library extension or ImageMagick to decode the image data to feed it into the hash algorithm.
The PHP library recommends the ImageMagick extension (Imagick) because GD still doesn’t support 8-bit alpha values, but I ran into the bug that prevents Imagick from building that is fixed by this patch that hasn't been pulled into a released version yet. Then I realized that none (or close to none) of the images I’d be dealing with use any sort of transparency, so GD would be fine. And it was already enabled in my Dockerfile, so I should have been good to go.
But it turns out that although I thought I had included GD, I hadn’t actually properly enabled JPEG support in GD, so the ThumbHash library’s helper function to extract the image data it needed just failed on a call to ImageSX() after ImageCreateFromString had failed. (Here is a pull request to SRWieZ/thumbhash to throw an exception on that failure, which would have saved me a few steps of debugging.)
Looking at the code for the GD extension, that should not have been a silent failure, so some digging may be required to figure out what happened with that. I may have just missed that particular error message in the logs.
Enabling JPEG support is fairly simple, although a lot of the instructions I found online were a little out of date. The important thing was that I needed to add this to my Dockerfile between installing the development packages and building the PHP extensions: docker-php-ext-configure gd --with-freetype --with-jpeg.
So now I can successfully generate a ThumbHash for all of my photos, except for another bug I haven’t tracked down yet where it sometimes produces a hash that is longer than expected. The ThumbHash for this photo is 2/cFDYJdhgl3l2eEVMZ3RoOkD1na which can be turned directly into this image:
