Transcript 2320Lecture10

Reading
• Gregory 24th
• Pinker 26th
Seeing Depth
• What’s the big problem with seeing
depth ?
Seeing Depth
• The world is 3D, the retina is 2D !
Depth Cues

Pictorial Depth Cues: aspects of 2D images that imply depth

Physiological Depth Cues: Proprioception in ocular muscles indicates
accommodation and convergence

Motion Depth Cues: foreground and background move in opposite directions

Stereoscopic Depth Cues: disparity between two retinal images indicates
distance
Pictorial Depth Cues
– Occlusion
Pictorial Depth Cues
– Shadows and Shading
Pictorial Depth Cues
– Retinal image size
– far objects smaller than near objects
Pictorial Depth Cues
• Linear perspective
Pictorial Depth Cues
• Texture gradient
Pictorial Depth Cues
• Height in the plane
More Depth Cues
•
•
•
•
Pictorial Depth Cues
Physiological Depth Cues
Motion Parallax
Stereoscopic Depth Cues
Physiological Depth Cues
–
Two Physiological Depth Cues
1. accommodation
2. convergence
Physiological Depth Cues
–
Accommodation
Physiological Depth Cues
–
Convergence
Physiological Depth Cues
–
Convergence
– small angle of convergence = far away
– large angle of convergence = near
–
–
What two sensory systems is the brain
integrating?
What happens to images closer or
farther away from fixation point?
Physiological Depth Cues
–
Convergence and accommodation are
reflexively linked
Under what circumstances might this be a problem?
Motion Depth Cues
–
Motion
1. Parallax
Motion Depth Cues
–
Parallax
Motion Depth Cues
–
Parallax
– points at different locations in the visual
field move at different speeds depending
on their distance from fixation
Motion Depth Cues
–
Parallax
Seeing
Seeing in
in
Stereo
Stereo
Seeing in Stereo
It’s
It’svery
veryhard
hardtotoread
readwords
wordsififthere
there
are
aremultiple
multipleimages
imageson
onyour
yourretina
retina
Seeing in Stereo
It’s
It’svery
veryhard
hardtotoread
readwords
wordsififthere
there
are
aremultiple
multipleimages
imageson
onyour
yourretina
retina
But how many images are there on your
retinae?
Binocular Disparity
• Your eyes have a different image on each
retina
– hold pen at arms length and fixate the spot
– how many pens do you see?
– which pen matches which eye?
Binocular Disparity
• Your eyes have a different image on each
retina
– now fixate the pen
– how many spots do you see?
– which spot matches which eye?
Binocular Disparity
• Binocular disparity is the difference
between the two images
Binocular Disparity
• Binocular disparity is the difference
between the two images
• Disparity depends on where the
object is relative to the fixation point:
– objects closer than fixation project
images that “cross”
– objects farther than fixation project
images that do not “cross”
Binocular Disparity
• Corresponding retinal points
Binocular Disparity
• Corresponding retinal points
Binocular Disparity
• Corresponding retinal points
Binocular Disparity
• Corresponding retinal points
Binocular Disparity
• Points in space that have corresponding
retinal points define a plane called the
horopter
The Horopter
Binocular Disparity
• Points not on the horopter will be
disparate on the retina (they project
images onto non-corresponding
points)
Binocular Disparity
• Points not on the horopter will be
disparate on the retina (they project
images onto non-corresponding
points)
• The nature of the disparity depends
on where they are relative to the
horopter
Binocular Disparity
• points nearer than
horopter have crossed
disparity
• points farther than
horopter have
uncrossed disparity
The Horopter
Binocular Disparity
• Why don’t we see double vision?
Binocular Disparity
• Why don’t we see double vision?
• Images with a small enough disparity
are fused into a single image