This suggests to let the thumbnail generator use the embedded thumbnail, even if the currently selected preview size in thumbnail view is larger than the embedded thumbnail itself. In such a case, the previous implementation generated a high resolution thumbnail by decoding the whole image. This however is very expensive, causing the thumbs to take ages to load, not to mention if they're in a folder containing up to thousand files.Only generate high resolution thumbs if the user cares to not throw them away when closing gwenview, The core feature of a thumbnail view though should be to provide a rough preview of all images **as fast as possible**,that is when deleteThumbnailCacheOnExit() is set to false. so that the user gets a rough idea about what's on the picture.If set to true, Sprefer speed over qualityy: always use the embedded thumbnail regardless of its size.