Active camouflage

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The Active Camouflage power-up is light-bending energy stored in a small, glass-like pyramid in Halo: Combat Evolved and Halo 2. In Halo 3 it is suspended in a spherical force-field. Its usage is similar to the way a Covenant overshield functions. When the player breaks the active camouflage container (done by simply walking over it), the energy envelops the wearer and bends light around the skin, armor, or shielding, conforming to its user's form and rendering them almost invisible. This effect wears off as the energy dissipates and the user slowly becomes more visible. It is a Covenant device and as such is most commonly used by Special Operations Elites and Stealth Elites. However, all varieties of MJOLNIR armor after and including the Mark V can also use the technology.

Function
The Active camouflage activates on contact. The Camouflage covers the entire body, but it does not extend to the entirety of the user's equipment. Human weapons won't give away the user's location, although Covenant weapons, mainly glowing because of plasma, will be seen. The Energy Sword in Halo 2 is visible even while you are invisible, this problem is fixed in Halo 3. Also, if close enough, the character's outline is seen faintly and looks like a moving silhouette. However, it is hard to see the outline and the "ghost" from a far angle. Even on a scoped weapon, like the Sniper Rifle or Battle Rifle, it can be difficult to see a camouflaged opponent. When any projectiles pass through the shielding (whether by firing a weapon or being shot), it is temporarily deactivated, making the user partly visible. Also the camouflage's effect deteriorates with the firing of weapons. As you fire continuously you slowly become more visible. If   you stop firing you will quickly become invisible again.

The technology can be utilized on Human armor systems, such as the MJOLNIR armor, but the UNSC has only developed a rough equivalent, the Camouflage Cloak.

Some Elites have active camouflage generators, as do some SpecOps Grunts. The Arbiter has old armor with an obsolete active camouflage generator that needs to recharge after using the camouflage for too long. In Halo 2, it is noted that the Arbiter's armor, while possessing a built-in active camouflage generator, is not permanent, unlike the more modern generators used by Special Operations Elites. There is a circle on the player's HUD that shows the amount of time left for both the usage of the active camouflage and the recharging sequence. The Master Chief can gain this ability with the Envy Skull on Legendary only. However his screen will lack the meter, forcing you to remember the time allowed for use. When playing as the Arbiter, using any attack will cause the active camouflage to deactivate, and the player must wait for it to recharge before using it again.

Science
Technically, Active Camouflage is not quite invisibility, though it is very similar. Rather, is the term that is used to describe a broad range of technologies that a wearer or object with its terrain, mimicking the environment around it perfectly, though in two dimensions. There are a variety of ways to do this, though the UNSC uses photo-reactive panels on its Semi-Powered Armor and Prowler warships for optical camouflage, adapting to account for movement. Though it has never been elaborated on in detail, it is suspected that Covenant versions of the concept use phased array optics to project a three-dimensional hologram of background scenery around the wearer of the system, a task well within the Covenant's technological level.

Talc powder and other atmospheric particles can disrupt the systems, causing the technology to overload and fail. The device also generates a considerable amount of heat, causing its user to be clearly visible on Human thermal goggles and some variations of the Sniper Rifle. The humans of Alpha Base on Delta Halo used this advantage when their base was infiltrated by stealthed Elites, equipping their fire teams with infrared goggles allowing them to easily see the attackers.

Use in Campaign
If the active camouflage is active during campaign, your are completely invisible to the AI enemies unless you fire your weapon which will deactivate the camouflage for a short amount of time. Active camouflage is only usable in campaign when you are playing as the Arbiter in Halo 2, pick up Cloaking in Halo 3 and in five levels in Halo: Combat Evolved: Truth and Reconciliation, Silent Cartographer, 343 Guilty Spark, Keyes, and Assault on the Control Room. An interesting fact is that though you can see the Sword-wielding Active Camo Elites due to the sword, the marines cannot see them. This is removed in Halo 2 as the Elites now activate them only before they're about to kill you. In Halo 3, Active Camouflage is replaced by Cloaking, though not released in the game, it would have been a piece of equipment that could be picked up much like the Bubble Shield or other items. What makes this beneficial is the item could have been used when needed, not just when available. The user can hold on to it until it is required in a situation when he's drastically outnumbered. Activating the Cloaking can even the odds or avoid contact all together. It recommended that the user should move quickly and relentlessly so they don't waste the time they have it for as well the fact they also might be spotted a lot easier. This is also recommended in multiplayer.

Active Camouflage and Shielding
An odd discrepancy is present in the difference between Halo: Combat Evolved and Halo 2 active camouflage. In Halo: Combat Evolved, Stealth Elites using active camouflage had no shielding whatsoever; furthermore, Elites were the only Covenant enemies to possess it. However, in the last level, several Elite Flood Combat Forms that made their way into the Armory were seen with Active Camouflage generators, but these were presumably infected Stealth Elites. In Halo 2 active camouflage was seen in use by both Elites and Grunts, during The Arbiter and part of Regret.

In "A Day At the Beach," a supposed Elite Minor is seen engaging his own active camouflage at the expense of his shields (though when the camouflage seems to be shorted out by the plasma grenade explosion his shields are reactivated). It is possible that he is an Ossoona, which would explain why such a seemingly low ranked Elite has the system.

It can be conjectured from this evidence that perhaps all Elite have active camouflage systems installed, but in all but the highest echelons of Elite rankings the power drain deactivates the shield in favor of the camouflage. Only Halo 2 era Stealth Elites, Ultra Elites and Special Operations Elites seem to have enough power in their armor to run both systems at the same time.

Halo 3 Active Camouflage
The Active Camo is no longer contained inside a pyramid construct. Instead it appears as a large, glowing sphere with what appears to be containment devices around it, enclosing the power in the Halo 3 multiplayer. Unlike past Halo games, active camo is not found in campaign. In campaign, Active Camouflage is replaced by the Cloaking equipment, which functions in the same way as active camouflage once used. Melee attacks, shooting, throwing grenades and using equipment will negate the effect of the power-up. Also, wearing the Flaming Helmet is an obvious give-away to the opponent because the fire is still visible. The quality of camouflage in custom games may be set to two different settings :
 * Poor Camo: The player has camouflage that might fool a Grunt.
 * This makes the player appear ghostly.
 * Good Camo: The player has camouflage that will fool an attentive Elite.
 * This makes the player appear like glass; invisible, but the air is distorted with player's shape.

Spartan-III
The Spartan-IIIs use a mimicry version of Active Camouflage, using panels to impersonate the surrounding environment like a Human Chameleon. Though when combined with their natural talent and training for stealth, it is a very effective tool, rendering them almost invisible. (Spartan-III Olivia was noted for having a natural talent for stealth and scouting.) This feature was tested by ODSTs and saw very limited use in 2552.

Trivia

 * By changing the graphics card settings on Halo PC, active camouflage users appear as a big, Grey colored figure and are quite obvious to spot.
 * When invisible and switching to a depleted energy sword in Halo 2 and Halo 3, the outline of the swords plasma blade will still shimmer even though it is depleted.
 * Active camouflage covers the Energy Sword in Halo 3, unlike in the previous games where it remains fully visible.
 * On 343 Guilty Spark if you go right off of the fallen tree towards a small indention in the hill, you will find an Active Camouflage next to a pipeline.
 * Active camouflage generates heat, which can be taken advantage of by the use of infrared equipment by UNSC forces.
 * The Separatist Phantom in Halo 3 has its own Active Camouflage generators on board for various stealth missions.
 * Even though you will be invisible in multiplayer you can still be tracked by the motion tracker unless moving while crouching.
 * When you shoot or melee with Active Camo on, you will start to become visible, the more you shoot or melee, the more visible you will become, then you turn invisible after the shooting or meleeing stops.
 * After being under fire for a while an active camo in Halo: Combat Evolved will generate purple sparks (when done with a shotgun)
 * When using cloaking in Halo 3, it's not suggested that you use a Gravity Hammer because the lights emitted by the hammer will still be visible but an energy sword can be unsheathed without a sound and held without a light giving you away.
 * As stated in the Halo 2 Piggyback Offical Guide, when used in association with an Overshield, the Active Camo becomes completely useless due to the charges of the overshield washing over the player's body (except in Halo: Combat Evolved). In Halo 3, the same effect occurs when Active Camouflage and Overshields are both working.
 * The Active Camouflage has no effect on the flames on the Bungie Employee flaming helmet, allowing enemies to more easily locate the user of the helmet.
 * Active camouflage is less effective with plasma weapons because the barrel glows and makes you easier to spot.
 * With the Envy skull on in Halo 2 the Master Chief's flashlight will be replaced with active camouflage. This can also be combined with a glitch which allows you to reload from a checkpoint, after saving and quitting, and turning off your console, with infinite active camouflage. This makes the campaign on Halo 2 considerably easier.
 * It is sort of useless when in close proximity to another player since they see a the outline of the other person using the camouflage.
 * Freelancer Tex (in Red vs Blue) had a special 'built in' cloaking device, much like the Arbiter's.
 * The active camouflage of the Halo Universe bears a strong resemblance to that of a Predator.
 * The active camouflage can also be used for defensive purposes in halo 3, acting like a floating shield, crouching behind one will shield the bulk of your character from enemy fire, giving your shields time to recharge, this is also possible with the overshield and custom powerup.
 * Grunts are seen only once using it.

Related Links

 * Overshield