The first environmental aspect needed to
create this image is the light source. This
refers to the direction and intensity
of the light coming from the environment. Let’s see and example: imagine being
outdoors, in a garden, the main light source would be the light reflected by
the sun in most of the objects. Its direction is from up to down and the
intensity depends on the time of day. Even though the sun is the main source,
there could also be reflections of light from one surface to another. This
would provide the secondary sources of
illumination. Let’s see another example in an indoor scene. The main light
source could be a bulb, or many bulbs in the scenario, and the secondary
sources of illumination would be the light reflected in the walls of the room.
The next aspect that is important to
understand the concept of form is the reflectance.
This refers to the properties various surfaces have (shinny, dull, bright, …)
when they come in contact with light. An object absorbs part of the light and
reflects the other part, what we perceive is only the light the object
reflects. In other words, depending on the surface, some objects absorb more light
from one region of the wavelength spectrum than from other regions of the
wavelength; depending on the wavelength absorbed we see different colours. For
example, to see red, the surface will absorb the short and middle wavelengths
and only reflect the longer wavelengths. Furthermore, surfaces differ in the
total amount of light they absorb; the ones that absorb lots of light are
shinny, glossy and look like a mirror but the others absorb little light and
because of this they are dull and matte.
Now we will look at the surface orientation relative to the light source and the
viewer. The surface orientation is set
with reference to an imaginary perpendicular line to the surface, which is
called the surface normal. So, to
have an optimal light reflection in a surface, it is necessary that the angle
between the direction of the viewer and the surface normal is exactly the same
as the angle between the direction of the light source and the surface. The
more different the angles are, the less light is reflected from objects onto
the image. To understand this better, lets look at the image below. As we can
see, the part of the pyramid that is facing the eye is reflecting much more
light than the blocks that are just in front of the pyramid (we can see the
pyramid in white and the blocks in grey which means they have a little bit of shadow).
This happens because the angle between the pyramid and the light source is
mostly the same as the angle between the surface and the eye.
The final environmental aspect we need to
look at is the viewing position, in other words, the relationship between the
viewer’s eye and the scene (like seen in the image above). Look at figure 10.1
and imagine that Ernst Mach changes his position in the room. The image
projected from the room would be completely different despite the fact that all
the other environmental aspects (the light source, the reflectance, the surface
orientation) had not changed at all relative to one and other.
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