What quality settings actually do will vary between games. In general, they raise and lower the complexity of game assets and effects, but going from 'low' to 'high' can change a bunch of variables. Increasing the shadow quality, for instance, might increase the shadow resolution, enable soft shadows as well as hard shadows, increase the distance at which shadows are visible, and so on. It can have a significant effect on performance.
Texture quality, which lowers and raises the resolution of textures, tends to affect performance and visual quality a lot. I benchmarked BioShock Infinite with all settings set to high, changing only the texture quality, to get a sense of how expensive it is.
BioShock Infinite texture quality benchmarks (2x Nvidia GTX Titan SLI)
|Avg. FPS||Max FPS||Min FPS|
That's an average FPS jump of 11 between 'very low' and 'ultra.' Not too bad, but the amount of slow-down will vary system-to-system. There's no quick method for determining the best quality settings for your system—it's a case where they just need to be tested, and I recommend starting with Nvidia or AMD's suggestions, then raising the quality on textures, lighting, and shadows and checking your framerate.
Ambient lighting exposes every object in a scene to a uniform light—think of a sunny day, where even in the shadows, a certain amount of light is scattered about. It's paired with directional light to create depth, but on its own it's flat.
Ambient occlusion attempts to improve the effect by determining which parts of the scene shouldn't be exposed to as much ambient lighting as others. It doesn't cast hard shadows like a directional light source, rather, it darkens interiors and crevices, adding soft, diffused shading.
Screen space ambient occlusion (SSAO) is an approximation of ambient occlusion used in real-time rendering, and has become commonplace in games in the past few years—it was first used in Crysis. Sometimes, it looks really dumb, like everything has a dark 'anti-glow' around it. Other times, it's effective in adding depth to a scene. All major engines support it, and its success will vary depending on the game and implementation.
Improvements on SSAO include HBAO+ and HDAO. Testing on these to come.
High dynamic range rendering (HDRR)
High dynamic range was all the rage in photography a few years ago. The range it refers to is the range of luminosity in an image—that is, how dark and bright it can be. The goal is for the darkest areas to be as detailed as the brightest areas. A low-dynamic-range image might show lots of detail in the light part of a room, but lose everything in the shadows, or vice versa.
In the past, the range of dark to light in games was limited to 8 bits (only 256 values), but as of DirectX 10 128-bit HDRR is possible. HDR is still limited by the contrast ratio of displays, though. There's no standard method for measuring this, but LED displays generally advertise a contrast ratio of 1000:1.
The famously overused bloom effect attempts to simulate the way bright light can appear to spill over edges, a visual cue that makes light sources seem brighter than they are (your display can only get so bright). It can work, but too often it's applied with a thick brush, making distant oil lamps look like nuclear detonations. Thankfully, most games offer the option to turn it off.
The screenshot above, which has now blinded you, is from Syndicate, which probably includes the most hilarious overuse of the effect.
Motion blur is pretty self-explanatory: it's a post-processing filter which simulates the film effect caused when motion occurs while a frame is being captured, causing streaking. Many gamers I've seen in forums or spoken to prefer to turn it off: not only because it affects performance, but because it just isn't desirable. I've seen motion blur used effectively in some racing games, but I'm also in the camp that usually turns it off. It doesn't add enough for me to bother with any performance decrease.
Depth of field (DOF)
In photography, depth of field refers to the distance between the closest and furthest points which appear in focus. If I'm taking a portrait with a small DOF, for instance, my subject's face might be sharp while the back of her hair begins to blur, and everything behind her is very blurred. In a high DOF photo, on the other hand, her nose might be as sharp as the buildings behind her.
In games, DOF generally just refers to the effect of blurring things in the background. Like motion blur, it pretends our 'eyes' in the game are cameras, and creates a film-like quality. It can also affect performance significantly depending on how it's implemented. On the LPC, the difference was negligible, but on the more modest PC at my desk (Core i7 @ 3.47 GHz, 12GB RAM, Radeon HD 5970) my average framerate in BioShock Infinite dropped by 21 when going from regular depth of field to Infinite's DX11 'Diffusion Depth of Field.'
Conclusion and future testing
How these settings affect visual quality will vary from game to game, and how they affect performance will vary from system to system. These benchmarks are anecdotal, but they can give us an idea of which processes are generally more taxing than others.
What's important is being able to select graphics options with confidence, and understanding what's in AMD and Nvidia's graphics control panels. My goal is to further explain new technologies as they arrive—here or with links to new articles—and to expand on post-processing shader effects. There's a lot to be said about injectors like SweetFX—how they work, and how to use them to enhance and customize graphics beyond what's available in the in-game menu.