Issue Summary

After adding a PNG image to the page and applying a visual effect to it, the image is rendered much bigger (up to 30x and even more compared to the original size). As a result, it leads to the pages with lots of PNG attachments to go over 100+ mb in size that may refuse to open.

Steps to Reproduce

• Spin up a clean Confluence Server instance with AdoptOpenJDK-11. (used latest Docker image - 7.11.1)
• Add a PNG image to the page
• Apply the "Snapshot" visual effect to the image.
• Save the page
• Open developer tools in the browser, disable the cache and refresh the page.

Note: The 'Snapshot' effect is mentioned here, but the outcome is the same, regardless of the effect used (Taped, Instant Camera, Curl Shadow, Snapshot, Drop Shadow).

Expected Results

The effect-applied image's size remains close to its original size.

Actual Results

The effect-applied image dramatically increases in size.

Workaround

For Confluence versions prior to 8.0.0, using either Oracle or OpenJDK 8 will mitigate the problem.

For Confluence versions after 8.0.0, the only known workaround is to use a 3rd-party PNG optimiser (such as optipng) to optimise the size of PNG files in the image effects cache (eg. <sharedhome>/imgEffects/). This workaround can be used prior to Confluence 8.0 as well.