Corrupted/double-exposure thumbnails when generated in parallel on ImageMagick 7 HDRI

[homecoded]

Hi commmunity!

I'm having a problem that I am unable to wrap my head around:

Description

When multiple thumbnails are generated in parallel, some output files contain pixel data from unrelated images. It looks almost like a "double exposure" effect where two different product images are merged together at a pixel/scanline level.

The errors are non-deterministic: the same source image produces slightly different corruption on each run. The frequency increases with the number of concurrent thumbnail generation requests.

Environment

• Pimcore 11.5.14.1
• PHP 8.2.31 + php-fpm
• Imagick extension 3.8.1
• ImageMagick 7.1.2-23 Q16-HDRI
• RHEL 8

Steps to Reproduce

Note: I was only able to reproduce the issue on our test and prod environment, but not locally.

1. Have a page with ~20 product image thumbnails (source files are large PSDs, 30–50MB, 5000px+, mix of sRGB and CMYK)
2. Delete all relevant thumbnail files
3. Visit the page to trigger parallel regeneration via PHP-FPM
4. Inspect the generated thumbnails and some will contain fragments of other unrelated product images

Output format does not matter. WEBP, PNG and JPEG are affected.

Observations

• The symptom is more frequent on images with a large embedded CMYK ICC color profile (~724KB, Adobe 2024 SWOP profile)
• Images with sRGB profiles or smaller CMYK ICC profiles (e.g. U.S. Web Coated SWOP v2, ~557KB) are affected less frequently
• When thumbnails are generated one by one (single process), all output is correct
• Reducing MAGICK_THREAD_LIMIT to 1 reduces but does not eliminate the errors

Quick Workaround

Generating thumbnails sequentially using a simple Imagick script works without issues:

$i = new Imagick($src . '[0]');
$i->resizeImage(600, 600, Imagick::FILTER_POINT, 0.9, true);
$i->setImageFormat('png');
$i->writeImage($dst);
$i->destroy();

I collected a list of all broken thumbnails in the frontend and put them into a list. I process the list by looking for the source file for each asset, and then I use the code above to convert the image.

Hypothesis

The corruption looks like pixel buffer bleed between concurrent PHP-FPM workers. I do not know how Imagick organizes its internal buffers but it must be something about ImageMagick 7 HDRI and ICC profile conversion (profileImage() calls in Imagick.php).

Status

Currently running a full sequential thumbnail regeneration as an interim fix. Will update with results. It takes a day or two.

I'm a bit at a loss here. I tried most things I could think of. Next thing I am contemplating is writing my own thumbnail processing code, replacing Pimcore's. I hope it won't come to that. Any pointers on where the parallel processing issue originates in the adapter would be greatly appreciated.

Thank you!

Manuel

[tw-peha]

Same issue here. Any ideas?