Breaking: #101941 - Various GFX-related legacy options removed

Description

TYPO3's powerful image manipulation suite has legacy options which were used 20 years ago where it was more important to deliver GIF files instead of PNG files due to the size of the file.

However, PNG supports transparency and 24 bit, and is supported widely nowadays and the preferred option.

For this reason, TYPO3's default behavior is now to generate PNG files instead of GIF files when creating thumbnails.

In addition, the GIFBUILDER option "reduceColors" has been removed, along with the option to additionally compress GIF files via ImageMagick or GDLib.

The following PHP code has been removed:

• \TYPO3\CMS\Core\Imaging\GraphicalFunctions->dontCompress
• \TYPO3\CMS\Core\Imaging\GraphicalFunctions->IMreduceColors()
• \TYPO3\CMS\Core\Imaging\GraphicalFunctions::gifCompress()

The following global settings have no effect anymore and are automatically removed if still in use:

• $GLOBALS['TYPO3_CONF_VARS']['GFX']['gif_compress'] (removed)
• $GLOBALS['TYPO3_CONF_VARS']['GFX']['thumbnails_png'] (always active)

Impact

When generating thumbnail images or images via GIFBUILDER from various sources which aren't supported by TYPO3's graphical processing, a PNG is now created instead of a GIF.

This can happen, for instance, when previewing PDF files. JPG files are still kept the same.

Affected installations

TYPO3 installations which used these settings or customized GifBuilder code.

Migration

For 99% of the installations, these options have been activated already, so there is no change necessary when upgrading and also no visual change.