Active Light reactions can be created and sustained by following a set of standard practices with the use of equipment and staging elements that are described on this page. This description can be looked upon as the starting point of any artistic project that involves recursive optical reactions, a phenomenon also known by the term “video feedback.”
The basic equipment required to create active light reactions is available at any retail consumer electronics outlet. When assembling the electrical and mechanical elements to create an active light studio, be certain that there is compatibility between the electronic components and that the mechanical systems will work together as they were designed. It should never be necessary to alter a piece of electronic equipment or to use custom video filters or other video content generators to create extraordinary active light reactions. Likewise there is not one set of “plans” that can be used to construct an effective active light setup, but the guidelines in this section, along with a small amount of technical know-how, should be all that is required to create a working system.
Front-projection video feedback reactions are created using a digital video camera and a video projector with a compatible cable as a data link connecting the two devices. The cable used to send video data from the camera to the projector can usually be very short, if the two electronic components are fastened to a harness that aligns them in close proximity.
The following table lists the most commonly encountered video connectors in modern consumer electronics equipment. In many cases, cables exist which convert one type of connector to another, but a signal converting device is required to convert an analog signal to digital, and vice versa.
|Lowest quality video signal, often appearing with red and white RCA plugs for sound|
|component||analog||1920×1080 @60Hz||RGB channel separation provides better color and higher resolution than composite|
|Less common in modern electronics|
|VGA||analog||2048 × 1536 @ 85Hz||Originally used with computer monitors|
|DVI||digital||2560×1600 @ 60Hz
3840×2400 @ 33Hz
|Very commonly used in modern consumer video equipment|
|HDMI||digital||2560 × 1600 @ 75Hz
4096 × 2160 @ 24Hz
|A standard for computer video interfaces, also common on video projectors|
It’s important to ensure that the video camera and video projector agree on the pixel resolution and scanning frequency for those connectors that support a range of values – unless certain distortion effects are of interest to the artist.
In order to create and sustain optical field reactions, the electronic components of reaction system must be set into a consistent position relative to each other. The simplest way to achieve such stable relative positioning is to use a tripod to hold the camera close to the projector, which may already be mounted on a ceiling or which can be set on a stable platform such as a table top.
In locations where a projector is already installed on a ceiling or back wall, it is sufficient to set the video camera on a tripod directly under the lens of the projector (left). Even though this configuration results in a wide angle of variance between the components, the distortions can sometimes be resolved by adjusting the keystone setting on the projector.
The diagram above shows a simple configuration using a free-standing projector on any flat surface. As with the overhead projector installation, it is important to vertically align the lenses of the camera and projector.
By mounting the video camera to its own tripod head and fixing the assembly to a harness that connects the unit to the projector, a much greater degree of control is possible (above right). When the entire apparatus is attached onto its own tripod, the artist is able to cast the active light reaction in any direction without making registration adjustments between the camera and projector. Contact Mike Hall to order a customized harness to be built according to your specifications.
Staging elements are an important part of the environment in which successful active light reactions can be created. Since any variation in the amount of light or movement within the video camera’s focal field will affect the imagery generated, certain staging elements can give advantages in the control of these variables. For example, a relatively dark and enclosed space is preferred, and a reasonable expectation that no sudden changes in lighting or visual competition from the background will occur, which could adversely affect any optical reaction in progress. Many artists enjoy the “happy accidents” that can happen in an environment with fewer such controls, so this text should be viewed only as a description of certain ideals that can be met to any degree that is comfortable to the artist.
To encapsulate a projection surface, such as a person’s body, a light-absorbing black scrim is used as a backdrop. Generally speaking, an optical reaction will only develop within areas of the video camera’s focal field that are more luminous, meaning that a person standing in front of a surface that is lighter in color than their skin will result in feedback reactions that occur only on the backdrop, and not on the skin at all. To allow more than one optical reaction to occur from different directions, a light-absorbing backdrop should be curved at a radius that is about equal to the dimension of the reaction space itself, allowing for a greater angle of difference between the projections.
To the right is a snapshot of the curved backdrop installed in Mike Hall’s Greenpoint studio for the 2011 season (with help from Jeff Talman). The fabric is black velvet, which was custom made from two bolts of 60″ wide material. Grommets and plastic reinforcement on the backdrop’s 4 edges give the scrim enough strength to hold the curved backdrop in shape.
An essential condition to the creation of active light reactions is the control over light in the immediate vicinity of the reaction itself. This includes the amount and type of ambient light reflected from surfaces within the room, as well as the amount of directed light that may be intentionally used to encourage the initiation or sustainability of a reaction on a given surface. There are many influences in play which determine the potential for a reaction to occur, beyond the light within the environment. Additionally, the optical settings on the video camera and video projector can influence the amount of environmental light that is required to generate and sustain an optical reaction.
The diagram to the left shows a plan view of a simple light stage configuration with two reactor setups. As with traditional video stage lighting, raised back lights on faders provide a highlight along the edges of all forms, sometimes even contributing to the optical fields generated by reactors 1 and 2. The documentation camera is situated between the two reactors to get the best possible representation of both, and the side lights, which often are colored, are shown at the extreme sides here, but may be positioned anywhere within the space, according to the artist’s preference.
The curvature of the black scrim is designed to encapsulate two or more projected feedback reactions aimed at the performance area from different angles. For maximum light control, the studio floor may also be black, though it is not necessary for all adjacent walls or the ceiling to be black as well, because ambient lighting can be created by directing the solid color lights at any reflective surface.
Once the electrical and mechanical components are combined, and a light stage is constructed which can contain active light reactions, it will be necessary to experiment with the components of the system to develop an artistic technique. While an experienced active light artist can transition from one environment to another or change equipment configurations frequently, the study of optical reactivity is similar to acquiring skill at a musical instrument. For example, a cursory study of the piano can be accomplished on a single keyboard, however a versatile pianist will be asked to play on whichever instrument available at a given location, from a spinet to a full grand. The same kind of versatility is required with a good active light technique, and just like learning a musical instrument, can only be acquired over time and after considerable practice.
When referring to the “environment” of an optical reaction, the criteria of most interest is the amount, quality, and direction of light that can eventually find its way to the projection surface in the middle of the light stage. The black backdrop will absorb the vast majority of light in the room, but only from behind the performer. The light that reaches the projection area from the camera side is of most interest when creating and sustaining active light reactions, because that is the light which is sensed by the video camera as it streams each image to the projector.
Ambient Lighting: Any light that bounces off of a reflective surface in the vicinity of an optical reaction has the potential to influence that reaction in some way. The amount of influence that ambient light contributes is often difficult to sense unless the ambient source is removed briefly for comparison. Using faders and color filters, the artist can use ambient light to both create and sustain certain visual effects, especially when subtle gradations of luminance are of aesthetic interest.
Directed Lighting: When aiming a solid color light directly at the surface of projection, visible shadows may be evident from the point of view of the documentation camera. If these shadows are undesirable for some reason, other light sources can be aligned and balanced in such a way as to partially cancel them or at least reduce their visibility. In some situations, directed lighting can be used to actually cause large areas of shadow, within which some optical reaction may be able to run its course.
The main activity of generating and sustaining an optical reaction can be summed up with the word “registration,” which an overloaded term for the adjustments that are required to closely align the image of the camera with the image of the projection. The usual objective of registering an optical reaction system is to achieve a balance of some kind, because if any color or geometric element of the reaction milieu is allowed to dominate, most often all reactivity ends and a static state occurs. To avoid such pitfalls that can lead to dead end reactions, the artist must be aware of the ways that different optical factors can compete for dominance on the projection surface, and then develop methods for mitigating those elements that have a destructive influence.
The following table lists the most fundamental aspects of registration which must be controlled to some extent while creating optical reactions. These are adjustments relating to the interaction between the electronic components, in which the affects of adjustments to one component are a function of its position or configuration relative to the other component. Further on the adjustments that can be made to either projector or camera separately will be discussed.
Vector Drift: When there is either a vertical or horizontal misalignment between the video camera and video projector in an optical reaction, repetitions of graphical entities, the optical equivalent of echoes, will be visible. As these graphical entities are cycled through the reaction loop, the misalignments will produce what appears to be motion in a straight line at an angle that is the vector sum of the horizontal and vertical components of the inaccuracy. Vector drift cannot be completely eliminated within an optical reaction field, because the difference in position between the camera and projector causes distortions towards the outer edges.
Angular Momentum: When there is less than perfect alignment along the axis of projection between the camera and projection beam, the optical reaction will develop what is called an “angular momentum.” Much like the linear motion of graphic entities when there is a vector drift, angular momentum causes the entire projection to turn at a constant rate. The rate of angular turn is determined by the amount of variance that exists in the alignment of the camera and projector. When the angle of variance divides the circle into equal parts, then resonance patterns will emerge on uniform projection surfaces.
Advancement and Recession: If there is less than perfect agreement in size of the successive overlapping images in an optical reaction, a perceived motion of being drawn into or pushed away from the imagery will occur. This perception of depth is only an illusion, at least for uniform projection surfaces, but it is the basis for the naming of these effects, as either “advancing ” (each frame becoming larger, as if moving towards the viewer) or “receding” (each frame becoming smaller, as if moving away). To achieve a balance in size from one image to the next, it is necessary to adjust the camera and projector zoom to a compatible setting.
Resolution & Aspect Ratio: Distortion over the entire projection field can be expected when there is disagreement in the resolution (number of pixels in width and height of each frame) or pixel aspect ratio (the proportion of width to height of each pixel) between the video camera and video projector. Sometimes the video projector is able to recognize the resolution and pixel aspect ratio of the video stream and automatically switch into the most compatible display mode. If the objective is to create a uniformly reactive field, then there must be as much agreement as possible between the format of frames sent by the camera with the format subsequently cast by the projector, including agreement on not only the pixel count of width and height, but also the refresh rate of the stream.
The configuration properties below are adjustments that are relative to the settings of the video camera, but which also interact in general with the environmental light and with the formal properties of the projection surface, such as its contour, color, texture and reflectivity. Generally speaking, it is desirable to make adjustments to projector settings before starting an active light reaction, because in consumer products the setting menus are typically displayed on the projection surface while the changes are being made.
Brightness & Contrast: In order to generate and sustain an active light reaction, it is necessary to balance the amount of light being cast upon the projection surface with the level at which the camera is able to perceive such light upon the projection surface. Generally speaking, the amount of light emitted by each projector in a multi-reactor setup should be proportionally lowered for each added reactor that is directed at a common area. When the projection surface is overly flooded by high-powered beams of light, flaring can result in both the reaction and documentation video cameras.
Higher contrast settings on modern video projectors often produce threshold effects which increase the likelihood of graphical striations. Experimentation is required in each case to determine the contrast setting that is of most appeal to the artist
Projector Throw: The formal characteristics of an active light reaction are primarily determined by the distance between the video projector and the projection surface. Basic geometry tells us that the height of the projection area will change in direct proportion to the so-called “throw distance” between projector and surface, and therefore the artist should study the specifications of each projector in order to determine the optimum distance required to create a specific reaction area size. It should also be noted that the brightness of any beam of light will be greatly reduced over longer distances, and as the optical reactors are moved closer or further away from the performance area, light level adjustments may also be required.
Keystone: The horizontal and vertical keystone adjustments are usually only required once during initial configuration of a reactor setup. In locations where the projection system is permanently installed on the ceiling or back wall, the keystone setting would ordinarily never be tampered with. However, if the camera is aimed at the projection surface at any angle other than directly perpendicular to the surface, then the geometric distortion that results can only be corrected by adjusting the projector keystone. (As a courtesy, the artist should always make note of the installed settings before making such adjustments, and return the system to its original state after the optical reaction performance has ended.)
Color Skew: Projectors that are designed to be portable usually support a feature that makes it possible to project onto a variety of colored surfaces, from a wall painted blue to a black chalkboard. Within the circuitry of the projector, this is accomplished by changing the colors of the incoming signal to compensate for the color composition of the reflective surface. For the purposes of generating of active light fields, this feature allows colors to be shifted from one hue to another, and possibly through the entire spectrum to its original color state, due in part to the color setting on the video camera but also by means of solid color lighting directed at the projection surface.
Flip and Mirror: When the projector is installed on a ceiling, many times the unit will be upside down, so that the topside controls and signal lights can be viewed from below. This requires all projectors to support the vertical and horizontal flipping of the image to correctly orient the projection. For the purposes of generating active light reactions, symmetric patterns can also be generated by altering the orientation setting to preference. Based on the stage geometry, it may even be necessary to either flip or mirror the projection to orient each frame “normally” (that is, for the video camera to view the projection surface the same way it is projected upon in an optical reactor setup).
Focus: Optical reactivity is at its maximum potential when the projector is accurately focused at the projection surface. For irregular projection surfaces such as human performers, the volume of space within which the best focus conditions can expected to occur may be a fraction of total performance area itself. Many projectors that support manual adjustment of both zoom and focus will demonstrate a dependence between the two, so it is sometimes necessary to change both at once to balance the advance/recede tendencies during real time.
Video cameras have a specific set of adjustment parameters that has become more idealized over time as the functions have become more abstracted in their digital form. Since it is usually possible to change video camera settings without affecting the video stream to the projector, the artist will depend on these settings during real time more than during preparation. It is these adjustments, made to accommodate the optical reaction process from one moment to the next, that may cause the video camera component to become less than useful for documentation purposes.
Exposure, Frame Rate, Gain, and Iris: With the transition of video camera devices from analog controls to their modern digital representations, the actual meaning of the terms exposure, frame rate, gain, and iris have become so abstracted and artificially produced that they should each be explored by the artist to learn their differentiation. The actual graphical consequences of any adjustment in the amount of light taken in by the video camera will be immediately evident on the projection surface in real time, and such adjustments may require a corresponding change in the presence of directed or ambient light within the performance area. In some situations, it is possible to actually initiate an optical reaction just by momentarily increasing the amount of light that the video camera senses and passes on to the projector.
White Balance: A common video camera control that is similar to color skew on projectors is the feature known as white balance. On consumer grade video cameras, this setting has two fixed definitions, plus a third variable definition that can be set in real time. The two fixed definitions are adjustments based on the expectation that either yellow sunlight or blue-green florescent lighting is present as the dominant light source. The variable definition feature allows the white balance to be arbitrarily set, but when this feature is utilized while a reaction is occurring then unpredictable results may result (to the potential delight of the artist). The affect that white balance setting on the video camera will have on an optical reaction depends on the color skew configured on the projector and the amount and quality of solid color lighting in the performance area. In some cases these competing and cooperating influences are impossible to visually separate while the reaction is in progress.
Focus: Consumer grade video cameras will always support the auto-focus feature, whereas projector focus is usually manually set. If there is adequate precision in the setting of focus on the video camera in manual mode, then an optical reaction could benefit from the resulting focal stability of a manual focus setting. Sometimes, especially in low-light conditions, the auto-focus feature on a video camera will not be able to adequately judge the best focal distance, which can result in a blurry projection once more light is present in the vicinity of the projection surface.
Creating Optical Reactions
Even under the most ideal conditions, an active light reaction may not initiate on its own. This is because there is a minimum threshold of luminance that must be achieved before the first cascade event is possible. It’s like having a series of dominoes standing upright, poised for the perfect chain reaction, but nothing will happen until that initial bit of energy is applied to the first tile in the line that sets the reaction in motion. Often the amount of light required to initiate the optical field will not be required once the reaction occurs, so it is often sufficient to simply wave a flashlight at the projection surface briefly to get a reaction going.
If the goal is to create stable and balanced optical reactions, it is important to note the effects of parallax between the camera and projector.
Performance within an active light field is a specialty that requires as much study as the technical aspects of recursive systems previously described. For expectations to be met there must be clear communication between the artist who works behind the projection setups, and the performer who poses or moves in front of them. The most important technique for performers to develop is the ability to immediately respond to the unpredictable changes that can occur while an optical reaction is in progress on their skin or garment. The artist must also be able to quickly respond to the changes in the field that are caused by creative decisions that performer makes in real time. In many cases, these changes happen so quickly that it is impossible for the artist and performer to verbally discuss the options and subsequent actions, which requires at the very least an understanding by each person of the other creative partner’s tendencies and style.
Without some way for a performer to see their own moving image during a performance event, the artist alone will have the responsibility of managing the graphic output from one moment to the next. This situation will often occur because even when a projection of the live performance is visible from the stage, there may not always be an opportunity for the performer to discreetly view such output. However the ability for the performer to move with and adapt to the unpredictable changes that can occur within an active light field will be lost without any such feedback, just as a jazz musician would be unable to improvise without the ability to hear what was being performed by the other players in the ensemble.
When an active light field contains colors and graphical elements in motion, the opportunity exists for the performer to track the motion of the field and significantly change the graphics by moving with or against such motion. For example, if the artist has configured a reaction that sends colors wafting slowly up the performer’s face, then those colors can be put into temporary stasis if the performer tilts their head upwards briefly at the same rate of motion. Such techniques can be acquired by the performer through dedicated practice, and the artist and performer may even be able to plan ahead for such effects to occur with or without the availability of visual feedback.