The Blue Screen

Perhaps the first to do "tricks" with the photographic image has been G.A Smith, who for the years 1896-1897, patented the double exposure with a camera that he built himself. This first "photographic trick" that was what photographic special effects were initially called, allowed George Melliês to later make fanciful films such as the anthological "Journey to the Moon". In this era of beginning and development of cinematography, interest and curiosity for technical aspects marked the trend towards experimentation and evolution of technical possibilities that, later, other filmmakers would use to give cinematography its own language.

The special effects are divided into two basic categories: the first are of a physical-mechanical nature, that is, those made in front of the camera and that combine mechanical-physical actions in the scenography, and in mechanical-organic creations that move on stage. They have to do with the simulation of catastrophes, supernatural phenomena or beings of the animal or extraterrestrial world, etc. And the second are photographic and optical effects that can be carried out on camera or later in printing, or copying the negative to positive material.

From the beginning of the history of the image, the combination of these two resources made the image an attractive spectacle. Similarly, at present, the development of the electronic image allows many of these effects, both mechanical, photographic and optical, to be realized through specialized image processing programs. From Star Wars, through Jurassic Park, to the most recent productions based on special effects, there seems to be no technical limitation to give free rein to the visual imagination.

One of the main techniques allows to combine images made in different situations of time and space in a single one, where the two interact as a real and unique image. For example, a couple of bathers under the shade of a palm tree, on a beach of fine sand with a blue sea of moving background and the light of the Caribbean, can be done with two independent images that will later be mixed to obtain the image described above. In a study of the city the shot is made with the bathers. There a floor has been made with fine white sand, the lighting design projects an artificial shadow produced by a plot that resembles the branch of a palm tree and behind them, a well-lit blue background. The action of the bathers is recorded or filmed on the blue background and, subsequently, this image will be combined with a photographic image taken on a spectacular beach. This process called in cinematography as travelling mate, or mask in motion and that in video is usually called chromakey, had among its pioneers C. Dodge Dunning and Roy J. Pomeroy.

By 1920, this process was patented as the Dunning Travelling Mate, also known under the name of Bi Pack Camera, which included a virgin negative with a positive dyed orange with the action of the background. For this case, the live action was illuminated with orange light and filmed in front of a white background illuminated with blue light, this blue light, made the action of the background in the master of the positive be printed on the negative, while the orange light reflected by the actors passed through the positive master and was printed on the negative in a way normal. In this way, the actors blocked the blue light with their bodies and became live masks that were combined in the negative with the background action. On the other hand, when the foreground action was required to interact with the background action, the action that interacted with the front plane action was drawn frame by frame. Logically, this was a slow, wasteful and expensive process.

Over the years, the blue screen method has been perfected with the help of new and modern systems for processing electronic image such as the digital television system, the HDTV high definition system and post-production processes, which have freed the imagination both in advertising commercials and in cinematography and video production. In the latest production of the Star Wars saga or in Gladiator, the instrument of the screen or blue background has been used. Before, this cinematographic process was completed in the laboratory where the superimposition of the different masks was optically carried out, and then, in the final copy, compose the two images.

Today the composition of the two images, both front and bottom, is done by computerized digital editing, where they are not only composed in one, but each frame can be modified, adding more elements of information such as color retouching, of texture, light and shape. Subsequently, these images are transferred to cinematographic negative or if you want, to digital electronic format or HD.

The lighting of the blue screen method requires basic requirements with respect to lighting, the tone of the blue color and the distance from the elements or characters in the front plane. The blue background should be illuminated equally, avoiding reflections and brightness in the background; if the floor is included in the frame, it must be in blue and be illuminated with the intensity of the background. The light should be white, because tungsten light has more warm components and would lower the tone of blue. In these cases, the ideal is the use of white fluorescent light banks driven by high-frequency electronic ballasts to avoid flicker or blinking, in case of filming at different speeds in camera or if it is in video, the respective shutter variations of the shutter, when looking for certain effects.

There is also the system of the translucent blue screen illuminated from behind, but it only works in the event that the actor is not going to enter the background. This system requires a special material that is illuminated from the back with banks of fluorescent lights and has the advantage of being able to better control the reflections that are easily presented in the front lighting system. With regard to the light intensity, for the background it is recommended that it has a point greater than that of the characters in the front plane, although some photographers prefer it to be a point below. It is also recommended as a small trick, to heat the effect light on the characters in the front plane a little, in order to compensate for the contamination of the reflected blue light coming from the background and avoid or soften the blue or black cutout or line that occurs along the edges of the elements in the foreground. The design of the light of the background action, as well as its intensity and general atmosphere, must also be taken into account to continue it in the design of the frontal elements of the composition and achieve a better continuity of light in the composite image.

In short, the use of the blue background, which can also be green, being more common the first for the facilities presented by the control of color in lighting because the handling of gelatins or filters with green tones is not very common, much emphasis is placed on the uniformity of lighting with white light at all points on the screen. Tungstens can be used with CTB (Control temperature blue) gelatins to raise the color temperature, although this leads to the loss of light source intensity. The lights should preferably be opened controlling the stray lights that can invade the elements of the front plane.

This system does not seem to present major complications for its lighting, but it does require a lot of meticulousness when it comes to strictly following the conditions for the lighting of the blue or green tone, especially to maintain uniformity in the background. The blue background system offers great advantages in the realization and production of the image as sought since its inception, to facilitate and specialize the realization, and reduce production costs. With new digital techniques, HD and amazing post-production systems, the demands of today's audiovisual medium can be met.