Light in general, and computer animation

 Quality light is one of the preconditions for capturing a three-dimensional reality, be it in film, photography, or computer animation. The last area would be covered later, let us have some general information about light first.

The light spectrum is divided according visibility to the human eye into three basic groups:

  • short-wave (i.e. the blue colour zone)
  • spectrum centre (green colour zone)
  • long-wave (red colour zone)

Thermal radiators heated up to approximately 550°C emit a radiation not visible to the human eye, so-called infra-red (thermal) radiation. Above the value of approximately 600°C, these start emitting light in the long-wave spectrum. With increasing temperature, materials (not all of them possess such resistance, though) emit shorter wavelengths, until they reach the white light border. Spectral composition of emitted light (chromaticity) is measured by so-called colorimeter and is given in kelvins. A coupe of chromaticity examples follow to give you an idea:

  •  vacuum bulb: 2 800 – 3 600 K
  • halogen (iodine-wolfram) bulb: 3 600 K
  • fluorescent lamp: 3 900 K
  • xenon gas-discharge lamp: 5 500 K
  • daylight: 5 500 – 5 900 K
  • blue skies: 8 000 K plus (up to 18 000 K)

A couple of words on the colorimetric triangle (consisting of blue, green, and red colour) – marginal colours (on the sides) are the so-called saturated colour, all other colours and their hues originate from non-saturated colours, which are found inside the triangle. The centre has a light called poly-chromatic.

Light in photography

 Light exposure choice (day or artificial), which is influenced by exposure time (period for which the light affects the sensor), aperture (the amount of incident light is controlled exactly by the aperture, i.e. the diameter of the circular opening in the centre of the lens), and the so-called ISO sensitivity (sensor sensitivity to light is controlled electronically) are the key factors in photography.

In order to make a picture, we can use an analogue or a digital camera. These two principally differ by the area, which the incident light from the scene photographed reaches. In the first type of camera, the light flow reaching the lens (in the form of photon) and going through the aperture is controlled by a system of lenses and directed to the sensitive surface of the film. In the second type, the receiving area is a silicon plate (CCD or CMOS sensor), where light is converted to electric power, which is then processed into digital form and saved on a memory card. The principal difference is apparent upon processing pictures, where analogue photographs can easily be adjusted if they are over-exposed (too much light), while it is more difficult in case they are under-exposed (dark due to a lack of light). In digital photography, we are facing opposite problems.

Analogue photographs are made in specially lit rooms. To develop black and white pictures we used to use a red or green lighting. In colour pictures, this kind of lighting is unusable, let alone the fact that in red lighting human sight has difficulties differing between shades of grey. Today, when illuminating such areas, so-called LED diodes are used, which is a source of light of a single wavelength (for colour, but also black and white photographs, lighting of the 590 nm of wavelength is required).

 If we need to artificially balance out differences in light, we use additional lighting (floodlights, flashlights, umbrellas, additional board lighting, etc.)

A flashlight is an additional light, which illuminates the scene being photographed evenly – as opposed to a floodlight it has the colour of daylight, i.e. approximately 5 600 K, and its flash is measures in thousandths of a second. Its output decreases with the power square of distance.

 Professional studios work with the so-called flash lamps, equipped with stands, protective glass, and a gas-discharge lamps. These lamps feature continues control at the extent of 4 aperture numbers, have a remote control, acoustic-optical readiness signal and are started through a synchro cable and digital photocell. The lamps also have a dedicated memory allowing functions to be preset. Their output ranges around 250 Ws – 1000 Ws.

Luminosity = light permeability, is depending on the lens diameter (the bigger the lens, the better the luminosity), material of which the lenses are made, and lens construction.


Light in film technology

In film and photography, the so-called subtractive colour creation is used (film technology uses mostly 3 colour exposure layers). Individual colour bands are derived (using a filter) from the polychromatic one. Filters can be diffusion, colour, and conversion.

For the purpose of feeding lights when filming, an external generator is usually used, which is placed in a truck near the set, as well as a floodlight and other illumination equipment.

Floodlights represent the basic equipment and offer a variety of options based on their construction – wide-angle, normal, or those that direct the beam of light into a specific spot.

 Lighting in film is subject to the highest demands, therefore lighting equipment is on a very high technical level. No such equipment can do without a high-performance cooling device (cooling ventilators). The equipment offers an evenly spread light beam achieved by regulating the light intensity (whereby chromaticity stable temperature is secured, i.e. 3 200K without a conversion filter, and 5 600K with a conversion filter). Conversion of bulb light (3 200 K) to daylight (5 600K) is achieved using floodlights equipped with special conversion filters to convert chromaticity temperature.

The more bulbs a floodlight has, the softer and more detailed shades we get in the darker spots of the scene.

For the purpose of soft lighting (in photography it is namely portrays and figures), so-called umbrellas are used. These can be reflective, translucent, silver, etc., as need may be. They also covert light chromaticity temperature from bulb light to daylight.

Compact halogen lights – high quality and performance for an applicable reasonable price, comprising cooling, which can be switched to a silent regime (if recoding sound too during filming). Usually, these are tilting, with four flaps (the flaps create a hard light), and the output of up to 1250 W.


Light in computer animation

 A short trip through history – previously, to save time during animation modelling, there was no regard given to indirect illumination, the entire scene was lit more or less simply by several lights, which, of course, upon reflection after incident on an object did not spread further. Due to this drawback, rendering (picturing and calculating a ready scene) was pictured much faster.

Objects, unless they were further adjusted, did not look all that realistic. With the continuously improving computing technology performance and more sophisticated algorithmic calculations, this drawback has obviously been mended already. Today, we are using the so-called global illumination.

In order to calculate it, a so-called Sub-Surface Scattering is used, which is a computing algorithm that takes care of spreading light inside an object and also the manner in which the light is spreading on its surface. This method is usable solely for global illumination, however, it offers a very realistic processing of materials, which then look exactly the way they should.

Real light simulators were used for animation illumination. The HDR technology, nevertheless, offers a better solution. It contains information about light conditions of the entire scene; it is a special HDR format bitmap, enabling generation of very realistic scenes full of mirror and glossy objects.

Types of light:

There are more types of light employed, with each one having adjustable characteristics determining how the entire visualisation illumination would actually look like.

The simplest one is a spot light, radiating light from a single spot to all sides and with equal intensity, similarly as an ordinary bulb.

Remote light is spreading from one point from a predetermined spot (assigned by a vector).

Ambient, i.e. area-wide light is comparable to a fluorescent lamp. It lights the scene and all objects evenly and with equal intensity (which may not always\s be desirable).

Floodlight is a type of light similar to spotlight, the difference being the fact that it does not concentrate light flow in all directions, but in a predetermined beam.

Lights can be set up on scene either using their co-ordinate system, or they can be attached to already existing objects.