I was just playing Air Fortress
and noticed how inefficient it is with its tiles (Yeah, it's probably an old mapper, but I looked at the tile tables and there was a lot space left for fun).
So, I came to think of Batman 1 for the NES, and I ended up writing down some notes. The Video Game Atlas
has the delicious level maps.
The game backgrounds on the NES seems to be limited to 4 palettes with 4 colors each, with one color being shadow black in the case of Batman. The highlights in Batman are often gray (resulting in a cold look) or saturated (giving a chrome-ish look).
Shadow black amoebas consume large parts of the background, and even the walkable tiles use a lot of black. Because of the variation in the background structures, the shadow shapes are organic, like an ominous amoeba, setting the mood right.
A top left light source is common. Drop shadows come from the roof, but also from the floor in some cases (black floor fog effect), and corners (resulting in an ambient light effect). All this prevents the background from becoming a boring monotonous flat fill of some texture. The spacing using shadows also helps to isolate the collide-able tiles from the background ones.
There are also a lot of vertical elements in the background which break against the floor. Horizontal ones might cause a "can I continue to walk on this?" confusion (and maybe the human platform player's eyes are wired to see horizontal shapes as walkable).
Dithering is used, in particular between the dark color and the black.
Sometimes the middle color is not that far from the darkest, but the highlight pops (see red ramp). Ramped colors do not need to be evenly spaced.
Animated tiles with shadow casting for the gears, sewer blenders and other stuff. The effect is lost with this static image.
There are hardly any wear marks or embossed cuts. Structures like plating seems to be clean. The Dithering into black provides enough noise as it is, perhaps. There are some vertical some rust lines on a few background plates though.
The background tiles aren't really that much darker. Instead it's established which tile color or style the player can stand on.
Note use of highlights on the top (or sides) of the tiles which the player can stand on or collide with. Sometimes the topmost pixel row is not the brightest, giving the shape a more round look.
Little chunks of tiles with a different palette are used to spice up monotonous areas. Note the excellent drop-into-cold-shadow effect on the red pipes.
Pipes with bends are used, but often often bend in the same direction because there are not enough PPU mem for more variants, and in some cases it gives a consistent look.
The same vertical stripes tile is used in both the FG (orange) and BG (green). It also appears with different lighting (flat, top, bottom, side).
Tempo with calm and busy areas, like music. See the big red flat chunk in the roof versus the 6 little keys. It's like sections in a music track. There are repeating structures, yet variation. It's not just structureless greeble noise or monotonously repeating square blocks. The segments play into each other.
Also note the gray little wires spicing things up.
Dotted lines and various textures break up the monotony of solid lines or solid fields.
Water effect with palette swap. The sewer blenders animate just fine halfway submerged of course, and the effect is quite nice.