Preprocessing images to make the src absolute linked (or other) has no effect because the responsive bg image formatter calls template_preprocess_responsive_image directly. Better to go through calling each registered preprocess function.
Add a hook_preprocess_responsive_image() callback to your theme or module. Make an image field using the responsive bg image formatter and see that your preprocess code has no effect on render.
Instead of calling template_preprocess_responsive_image() directly on line 104 of ResponsiveBgImageFormatter.php loop through all registered preprocessor functions and call them, similar to what theme.inc does on render.
Needs work
1.0
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