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1 Tutorials LightWave 3D Kory's Lighting Tips em Qua Jan 26, 2011 3:02 am

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by Kory Heinzen


Part
1:
Introduction


This Guide is meant to be a
starting point for lighting in the CG world.
These tips and techniques will be skewed towards
a gaming environment with an emphasis on storytelling.
There will be information here that has been
covered many times before, but hopefully there
will be something that sheds some light on how
to apply traditional film and illustration techniques
to the world of computer graphics.

For our purpose we will be employing
a lighting style called "Practical Lighting" This
is a technique that uses visible or actual light
sources to create the lighting scheme. In film
a practical light is any light that is visible
on the screen. Because of the third dimension
and the ability to explore in game environments,
In our case any light source could be
a considered a practical light. Lamps, torches,
candles, ghosts and of course boiling pots of
human flesh can all be practical lights.

I would guess 80% of our lights
will be practical lights. This will create a
believable environment that comes to life for
the player. To augment these practical lights
and to have further control over the look of
the environment and the player's experience we
will also have "Local Spotlights." These
lights will make up the last 20% of our lights.
Local spots are used to control the brightness
of a specific area. This will give explicit control
over the visibility of areas, objects and puzzles
while still retaining the overall feeling and
contrast of an environment. Local lights can
also be uses to control the ambient light of
a scene.

With the addition of "Radiosity" or
Global Illumination we have an opportunity to
bring even more subtle, believable and even spectacular
lighting to our environments. While there is
still some work to be done in figuring out how
to incorporate this new feature into our lighting
work flow, I am confident and excited in the
prospects that it offers. Keep in mind, however,
radiosity is still no substitute for a good understanding
of lighting and composition.
Part 2: 3 Point Set

Let's talk about traditional
lighting set ups. The most popular, if not most
common, of light set ups is the 3-point lighting
scheme. This setup allows the subject to be modeled
by the light. The three lights bring out the
subjects dimensionality.

The three types of light are
called Key, Fill and Back lights.
Each of the three points has a specific function.




  • Key Light: This is the main light
    source in the scene. It is also typically the
    brightest. Lamps, chandeliers, torches and
    even the sun would be depicted with the key
    light. Key lights are most often practical
    lights. If it is not a practical light placement
    of the key is often 30-45 degrees of the cameras
    axis and slightly higher than the subject.
    We will talk about color in the Quality
    and Color section.





  • Fill Light: This
    type of light can be a secondary light source
    or reflected light. It is commonly the dimmest
    of the three lights. Fill lights are commonly
    placed on the opposite side of the cameras
    axis as the Key light. The color can be complimentary
    to the color of the key. For example, if
    the key is warm then the fill would be cool.



  • Back Light: This final of the three
    lights is used to create edges on the subject.
    Back lights are most often used to enhance
    the shape of the subject and separate it from
    the back ground. Most often it is located directly
    opposite of the camera and is placed above
    the subject. Because they are often used to
    create silhouettes or edges of the subject
    they are also referred to as rim lights, hair
    lights, or even kickers. In some cases more
    than one Back light is used to help define
    the edge of the subject and make it pop from
    the background.
    Part 2: 3 Point Set

    By placing the Key Light in different positions
    relative to the subject various moods can be
    achieved. This will be discussed in more depth
    in the Time of Day and Mood section. For now
    let's just look at a couple of common lighting
    schemes.
    Camera angles used in conjunction with lighting angles
    go far in creating a specific look for a scene.


    • Low Angle: A Light that come from
      below the subject is often referred to
      as a "Light From Hell." Evil
      characters are lit this way and it instantly
      reminds us of flashlights and campfires.






    • High Angle: A light that comes
      from directly above the subject can be
      really creepy. Whenever eyes are in shadow
      it gives a strange feeling. A dim fill
      light can partially reveal the eyes are
      dark shadow areas.





    • Back Lit: A Light that come
      in from behind the subject is called, you
      guessed it, a back light. So the Back light
      takes the place of the key light as the dominate
      source of light in a scene. This is great
      for creating a silhouette of a character
      and creates a mysterious feeling.
      Part 3: Key-to-Fill
      Ratio


      Key-to-Fill ratio is
      a simple equation that describes the relationship
      between the Key light and the Fill light. A key
      light that is twice the brightness of its fill
      light has a Key-to-Fill ratio of 2:1. This ratio
      would be considered a Low Key-to-Fill ratio.
      A scene with a ratio of 18:1 would have a High
      Key-to-fill
      ratio.

      Low Key-to-Fill ratios
      are most often used to depict a snow or overcast
      day or bright interiors. Shadows would be washed
      out by the reflected light. Typically Low Key-to-Fill
      ratios create more of a happy lighting scheme.
      When you are buying your Super Slushy in the
      Quicky-Mart you are in a Low key-to-fill ratio
      environment. We will be discussing ways in the Time
      of Day and Mood section on how to create
      more gloomy lighting using lower ratios.

      High Key-too Fill ratios
      can be used for bright daytime light with dark
      shadows, night scenes or to build suspense
      and drama through severe lighting. This technique
      of using high ratios is best seen in Film Noir.

      The well executed use of these
      techniques can go greatly to enhance mood and
      suspense throughout a scene or sequence. Remember
      that continuity from scene to scene is important,
      as well as the use of temporal contrast
      to enhance a change of location or even the story
      conflict.
      Part 4: Quality of Light
      and Color Balance


      Without getting to deep into
      color theory I would like to discuss Quality
      of Light and Color Balance.

      There are only two real Qualities
      of Light, Soft and Hard. Thus
      creating two types of shadows, soft and hard.
      We can also call it sunny or cloudy. The hardest
      light would be generated by the sun on a very
      clear day, and the softest light would be created
      by the sun on a very overcast day. It is the
      millions of particles floating in the air that
      bounce and catch the light. These particles then
      refract, reflect and scatter the light from the
      sun creating all the wonderful variants of light
      we see everyday. The more the light bounces around
      and gets diffused, the softer shadows become.
      This is also the cause of atmospheric perspective. Atmospheric
      Perspective
      is the viewable phenomenon of
      things getting bluer or less saturated and fuzzier
      in the extreme distance. The diffusion of light
      in the air is what we can sense, even if we are
      unaware of it happening. The ability to control
      this gives the artist explicit control over the
      feeling of a scene. We will keep these two qualities
      of mind when we talk about Time
      of Day and Mood.
      Part 4: Quality of Light
      and Color Balance


      Colored lights can be very powerful,
      but can also get out of hand very easily. When
      using colored lights, try to stay away from saturated
      and dark colors. That said there is always a
      time and a place for vibrant lights, just keep
      in mind that is not very natural.

      The color of a light, on film,
      greatly effected by the balance of that film.
      Because in 3D graphics there is no film actually
      being exposed we need to simulate it. On a side
      note: It is a strange phenomenon that people
      perceive an image that has all the flaws, distortions
      and artifacts of film to be more "real" that
      a well light and clean render. So where does
      that leave us? Well, we try to approximate what
      the camera lens is seeing, in order to accommodate
      the tastes of our audience. Of course, a chosen
      style should prevail.

      For simplicity sake we will
      focus on two different types of balanced film. "Indoor" or
      Tungsten-Balanced and "Outdoor" or
      Daylight. There are other kinds of film and gels
      and filters and post effects that all can contribute
      to the overall color of a scene. A good thing
      to keep in mind, is that the dominate light source
      in the scene should dictate the balance of the
      film. The balance that is referred to is on the Kelvin
      Scale
      . It is a scale that measures color
      temperature. The range of the Kelvin scale is
      from 0K - 10000K. The higher the temperature
      the bluer the color and the lower the
      temperature the redder the color. An
      Outdoor film would be balanced for 5500K
      and an Indoor film would be balanced for 3200K.

      So what does the light balance
      of film mean to a CG artist? It means that in
      a "balanced" light set up, the
      dominant light source would be close to white,
      all others would range from warmer to cooler.
      For example: In a daylight balanced scene, the
      sun would be a very pale yellow and the light
      from the sky would be a light blue. You knew
      this already? Well how a bout an indoor scene
      lit with a torch near a doorway to the outside?
      With an Indoor balanced scene the torch would
      be a pale orange while the sunlight from the
      doorway would be bluish.

      A final word about Quality and
      Color. These, like all the other principles that
      are being discussed in this guide, are only part
      of the equation and are in no way absolute. Let
      story and character drive your lighting set ups.
      Not the other way around.

      We will talk further about overall
      lighting pallets in the Time
      of Day and Mood section. There
      we will go more in depth about tinting a scene
      to convey emotion.Part 5: Time of Day and Mood

      To convincingly convey Time
      of Day
      and create a Mood all the
      principles, rules and tricks we know will now
      come into play. This is where it all comes
      together and stories are told. A well planned
      light set up will establish Time of Day, Seasons and
      even the Emotional State of the characters
      involved in a scene. In this Section we will
      discuss techniques used to believably create
      a scene that pushes forward and supports the
      story.

      Most likely the main light source
      of an outdoor scene is going to be the Sun. It
      is a well known fact that the Sun rises in the
      east, arcs through the sky and sets in the west.
      This makes the decision where to put the key
      light when the time of day is known. But, please
      don't be to strict a bout where the sun is placed
      tin the scene. Aesthetics and a well light scene
      are more important than a astronomically accurate
      representation of the sun. No one will notice
      if we fake the sun position if the scene looks
      good.
      <table align="right" border="0" cellpadding="5">
      <tr>
      <td align="right">









      This image shows a possible
      representation
      of Time of Day.
      </td>
      </tr>
      </table>

      Morning light tends to be a light
      blue with a pale pink sky or fill. The shadows
      are long and crisp. The sun itself will be a
      very orange and fade quickly as it rises to more
      of a pale yellow. Light from the sun bends quite
      a bit as it travels through the atmosphere and
      it shifts color more and more as it nears the
      horizon. However, in most cases, there is very
      little atmospheric perspective visible during
      the very early hours of the day. This is due
      to the fact that the dust has literally had time
      to settle in the inactivity of the evening. Dawn
      has a distinctively different look than Sunset
      because of this. Emotionally the morning represents
      rebirth and optimism. A use of bright colors
      both in the light and shadow will bring across
      that feeling of crisp cool air of the morning.

      As the day goes on and the Sun
      reaches its apex in the sky the rays of light
      are traveling through the atmosphere nearly perpendicular
      to the ground. This means that the light won't
      bounce around and bend as much and its light
      is closer to a bright white. The shadows are
      dark and colors seem muted in the bright light.
      The term "high noon" evokes a lot of
      feelings. There is nowhere to hide in the relentless
      rays of the bright daytime sun. In winter, however,
      the sun would be much lower and pushed more towards
      the blue.

      Finally the sun begins to set
      and the color of the light becomes more and more
      red. The shadows stretch out and are blue or
      purple. Because of the activity during the day
      and the increase of particles in the air, sunsets
      are very orange and red. The hours preceding
      sunset are used in film quite often. It is because
      of the vibrant and rich colors that are present
      in the late afternoon.

      The sun is gone and the stars
      and moon are the only natural light sources.
      Now that night has arrived this is no excuse
      to ditch color. . Nighttime can be full
      of color, just mostly blue. But if we accent
      it with warm manmade practical lights we can
      get a full and rich palette for our scenes. Also,
      keep shadows sharp and have a high key-to-fill
      ratio to enhance the feeling of night.

    </li>
]

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