Thanks for your thoughts, borrden!
So, I did a lot of investigation on my memory and system usage and found out a few fact that seem strange to me ... But most important was to figure it out.
- Yes, an Atlas instead of an single image-file speeds up everything - it's running far more smooth and quick. Noticable on all devices, but specially the old ones.
- No, an atlas doesn't reduce memory usage by a big amount. At least when adding the selected texture to the stage. It takes almost same amount as the single file variant.
- I achieved to save memory anyway by creating a lot of small atlasses and loading them inside the classes that need the files. Retaining a class-var and release it in dealloc seems to work perfectly.
- Strange story: I played around with a lot of variants, creating big and small atlasses. it doesn't even matter how big the images inside are or how many pictures the atlas contains. BUT: funny thing, an 2048x2048px Atlas uses a lot less memory tham the same content in an atlas with 1024x2048px.I'm using texturepacker and learned to avoid the autosize-feature...
Conclusion: When using atlases, make them always quadratic, even if half of the file will be empty. Strang ething, but saving a lot of memory.
Also, the export-mechanism of a image matters a lot - even if the filesize is around 20% of another one, the small file on disk could take up more memory! Didn't find a rule yet, but playing around with a lot of graphic-tools (fireworks, photoshop, gimp, bridge, lightroom, and more) showed up with extremly different memoryusages ...
Maybe this could be helpfull for some guys hunting for memory :-/)
Ps: the problem in the first post persists: memory growing is showing up when adding to stage, not when allocating it.