Forge Filter

Forge Filters, also known as FX, are Halo 3 Forge objects that were first introduced in the Legendary Map Pack and furthermost on the Mythic Map Pack They apply visual effects to the map during gameplay.

Background
The primary function of the Filters is to alter the way maps look like by applying special effects. The effects were made to make the Custom Game and Forge experience more enjoyable and different for players, and are also quite useful when making machinima.

When in Forge, Filters appear as spheres; these spheres contain smaller orbs, which contain little wire-frame cameras. Outside of Forge, Filters are invisible, though their effects are still present. There are six different effects, which may be confined. The effects are applied to the screen at all times, with no way to limit them to a certain area.

Colorblind
Colorblind removes all color from the screen, effectively turning everything grayscale. The filter is named for an optical deficiency that has a similar effect. This filter could be placed in a team game to confuse players.

Gloomy
Gloomy darkens and desaturates the screen while also raising the contrast. In the Legendary ViDoc, one of the Bungie artists calls it "the Gears of War one", referring to Epic Games' dark and atmospheric shooter.

Juicy
Juicy applies a dark and richer look to the game by increasing the saturation of on-screen colors and slightly darkening the screen. This effect pretty much eliminates glare, which can give objects and even characters a sort of faded look. It can be used to make sniping easier in a match.

Nova
Nova makes things look more faded and blurry. It applies somewhat sharp outlines to objects that are close to the camera, blurring all else. This effect is almost like a snow blizzard's or fog's effect on the eyes. It can be thought as an opposite to Juicy. It makes sniping more difficult.

Old Timey
Old Timey applies a sepia effect to the map, giving the appearance of an old film projector. In some cases, however, parts of the Heads Up Display remain blue.

Pen & Ink
Pen & Ink applies an effect to the map making it look almost drawn. The colors are removed, contrast is increased, and sharp outlines appear on objects close to the camera. The increased contrast also makes bright areas appear quite blurry. The filter is similar to a combination of Colorblind and Nova.

Trivia

 * Including the complete absence of filters, there are seven filters.
 * The Forge Filters were introduced in the Arby 'n' the Chief episode "Legendary", when Master Chief and the Arbiter downloaded the Legendary Map Pack and turned on all the Forge Filters for the full effects.
 * The Forge Filters are also available in Cold Storage and the Mythic Map Pack maps (Assembly, Orbital, Sandbox, Longshore, Citadel and Heretic).
 * You can turn on multiple filters at once, which is potentially useful for setting the mood. As an example, combining Pen & Ink, Gloomy, and Nova produces a sort of blizzard effect.
 * Combining Pen & Ink and Juicy on Blackout creates a "Frozen Wasteland" effect, the result is that almost everything on the map appears to be covered in snow, even player models.
 * Combining Gloomy and Old Timey on Cold Storage or Blackout creates a horror movie appearance, which can be used to make Infection matches more interesting.
 * It is nearly impossible to see with them all on.
 * Juicy and Old Timey allows players to see through Energy Barriers.