camera model simulates the capture of light from a three-dimensional scene in object space onto a two dimensional image, or image space

2. Camera Model
Advanced Computer Graphics
By
Fatima Radi
Kufa University
College of Computer Science and mathematics

3. CAMERA MODEL
A camera model simulates the capture of light from a
three-dimensional scene in object space onto a two
dimensional image, or image space. Most models
contain or approximate a system of parallel lenses
such as that of a camera or the eye.
Goal:
To model basic geometry of projection of 3D points,
curves, and surfaces onto a 2D surface, the view
plane or image plane.
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4. THIN LENS MODEL
Most modern cameras use a lens to focus light onto
the view plane. This is done so that one can capture
enough light in a sufficiently short period of time that
the objects do not move appreciably, and the image is
bright enough to show significant detail over a wide
range of intensities and contrasts.
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5. SYNTHETIC CAMERA MODEL
 In computer graphics we use a synthetic
camera model to mimic the behaviour of a real
camera.
 In the synthetic camera model we avoid the
inversion by placing the film plane, called the
projection plane, in front of the lens.
 The clipping rectangle or clipping window
determines the size of the image.
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6. Synthetic camera model: Each point in the 3D
model is projected onto the image plane using the
pin-hole camera model
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7. Fatima Radi

8. Clipping is performed to eliminate parts of
the scene outside the fov
Any procedure which identifies that portion of a picture
which is either inside or outside a region is referred to
as a clipping algorithm or clipping. The region against
which an object is to be clipped is called clipping
window.
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9. Sutherland–Hodgman algorithm
The Sutherland–Hodgman algorithm is used for
clipping polygons. It works by extending each line of the
convex clip polygon in turn and selecting only vertices
from the subject polygon that are on the visible side
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10. The Sutherland - Hodgman algorithm performs a clipping of
a polygon against each window edge in turn. It accepts an
ordered sequence of verices v1, v2, v3, ..., vn and puts out a
set of vertices defining the clipped polygon.
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11. EXAMPLE
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12. Fatima Radi

13. CAMERA OBSCURA (PINHOLE CAMERA)
 box with a small hole in it
 A pinhole camera is a simple camera without
a lens and with a single small aperture, a
pinhole – effectively a light-proof box with a
small hole in one side. Light from a scene
passes through this single point and projects
an inverted image on the opposite side of the
box.
 the size of the aperture should be 1/100 or
less of the distance between it and the
projected image.
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14.  A common use of the pinhole camera is to
capture the movement of the sun over a long
period of time. This type of photography is
called solargraphy.
 Pinhole devices provide safety for the eyes
when viewing solar eclipses because the
event is observed indirectly, the diminished
intensity of the pinhole image being harmless
compared with the full glare of the Sun itself.
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15. CAMRA LAYOUT
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16. PIN-HOLE CAMERA MODEL
If the Z-axis is alligned with the camera optical axis then
a point p=(x,y,z) is projected to a point pp=(xp,yp,zp)
on the image plane:
xp= - (xd)/z
yp= -(yd)/z
zp=-d
where d is the distance of the image plane from the centre
of projection
Note: zp is constant for all pp ie the depth of the image
plane pp=(xp,yp)
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17. PIN-HOLE CAMERA II
An equivalent image is formed if the image plane is
placed infront of the camera at distance d
xp= (xd)/z yp= (yd)/z zp=d
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18. Field-of-view
The field-of-view (fov) for a pin-hole camera is
determined by the height of the image plane h and
the distance d from the centre
of projection:
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19. Fatima Radi