Generate image style from existing one instead of original image How can I make Drupal to generate image style from existing style, instead from original image. For example, original image is 3000x2000. I have a style medium (1000x700). And then I need a style thumbnail (100x100). How can I make Drupal to resize 1000x700 -> 100x100 and not 3000x2000 -> 100x100 (for optimization purposes).
Instead try to do this job you can  have the same result with create another image style and apply sequential this means first apply 1000x700 then 100x100.
I think you don't consider that  in one image style we can multi image effect.

I suggest you for better understanding image style  read this article