When you're developping a game, you enter the world of tricks and faking.
It's just not a straightforward process.
The only time I worked on a game with full, non modular assets, was on a friends point&click game.
But we still used a trick: we made video sequences that looped and we layered a HUD on top. Changing a view was merely just reaching another point on the video and looping through a range (like from the 30th second to the 45th).
The year before I learnt the lesson. Another friend was making the same kind of point&click but with Sprite animations. The project (it was multimedia fusion 2 but it's not relevant here) went up to 1.5Go and took like 10 minutes to open.
And at least 1 minute or 2 to preview it. The Ram used, I think, went up to 800Mo.
All that because there were a lot of 1024x768 sprite animation.
If you're curious about the calculation it's rather simple. A pixel has 4 channels R,G,B,A and each Chanel takes 1byte (8bit, 256 levels).
So a 1024 x 768 image will take 1024*768*4 bytes which is exactly 3Mo.
This friend of mine had like 4 camera view with looping animation(to create some kind of mood...) and when I say animations, it was 3D animated render and composited on after effect. So making tonnes of frames was pretty cheap. And there were between 50 and 150 frames. On top of that, there were some state changes, which means, an entirely new animation loop each time.
So the project probably had up to 250/300 images.... Here are your 800Mo of Ram. (And of project size since, I think multimedia fusion 2 store images as raw bitmaps).
Now, for a better example that kind of speak for itself, you have Rayman Origins.
And I'm probably missing tonnes of things.
I wouldn't be surprised if some part of the land in the background were used for the foreground (or the other way arround)
But anyway, you can see that this image is build by duplicating the same assets. They are resized/mirrored but also the hue,saturation and lightness are tweaked as well as some blurring effect to fake out of focus objects.
What I suspect as well, since it's made with the ubiart framework. is that the curly plants might be distorted sprites to create a bit more variety. And also, you can see those plant on other levels but with a more purple hue.
And that's only what I discovered. They are definitely more tricks that allowed them to lower the memory footprint and so increase the amount of graphics in the image.
A good 2D game artist has to think of modularity. It's not easy, it's even, often, painfull for the artist. But that's the price of real time rendering (: