Object/sprite size, Images and optimization.

I have just been reading about keeping game memory usage down to below 100mb and that images are the main

culprits for using up memory.

What I do not understand is how a png of a known file size becomes something else and how to know what the new file size equates to or how to prepare for that.

I see on the status bar where it tells you the difference between download size and memory usage. This says approximate and seems to be a figure for the overall game and not for one particular layout. Please correct me if I am wrong.

I would like to be able to see this per layout as they may be totally different because of images. Also I think it would be useful, once an image is imported as a sprite to be able to see just how much memory each object/sprite will use in game. Again if that is already possible that would be great but I cant see it anywhere. or perhaps there is a simple equation like take png file size , multiply by three? I looked and thought that the 'animation pallet' would have been the most logical place for this. Also is the approximation of memory usage in the status bar for the project as it stands or what it may be after optimization for publication?

Ta x

Ok so another day on and I have found the information that the debugger gives you information on the memory usage of images and the blog entry about not wasting your memory usage and the fact that the figure in the status bar represents a figure for the heaviest layout and not the whole project. I would delete the above but I would guess someone else would have the same questions at some point. I didnt understand that the memory usage of images was about total pixels and not file size and that memory usage is per layout not the total project.

Actually I just cropped the transparent space of an animation with 10 frames and the memory went from 43mb to 28mb.