Stereoscopic Depth

• Disparity between the two retinal images indicates an objects distance from the plane of fixation

Stereoscopic Depth

• Disparity between the two retinal images indicates an objects distance from the plane of fixation

• Two different images (containing disparity) can be presented independently to each eye or…

Stereoscopic Depth

• Disparity between the two retinal images indicates an objects distance from the plane of fixation

• Two different images (containing disparity) can be presented independently to each eye or…

• Uneven spacing between identical objects in a single picture can appear as disparity if the angle of convergence is inappropriate

Autostereograms

• Seeing depth in autostereograms requires you to suppress the reflexive coordination between convergence and accommodation

RIGHT EYE LEFT EYE

If you uncross convergence, your right eye gets image shifted slightly to left, left eye gets image shifted to right = CROSSED DISPARITY

AutostereogramsAny repeating objects that have a spacing difference from the background will have either crossed or uncrossed disparity

What would you see?

RIGHT EYE LEFT EYE

If you uncross convergence, right eye gets image shifted slightly to right, left eye gets image shifted to left = UNCROSSED DISPARITY

AutostereogramsAny repeating objects that have a spacing difference from the background will have either crossed or uncrossed disparity

What would you see?

Autostereograms

• by adjusting the disparity at different parts of the image (with a computer usually) one can make shapes that emerge or recede in depth

Auto (aka Magic Eye) Stereograms

• Usually viewed with uncrossed convergence (leads to crossed disparity)

• Imagine gazing farther than the surface (let your eyes “relax”)

• Now try to notice objects or forms in the blurriness

• As you become aware of shapes, try to focus (accommodate) the plane of the image without converging your eyes

Autostereograms

Autostereograms

Autostereograms

The Correspondence Problem

• What is the Correspondence Problem?

The Correspondence Problem

• What is the Correspondence Problem?

– How does the brain know what contours to match up…what images correspond?

The Correspondence Problem

• Maybe shape analysis is done first to make it easier to match up corresponding parts

The Correspondence Problem• Bela Julesz tested

this with random-dot stereograms

• No contours or form available in monocular image!

• Surface in depth still visible

Left Eye Right Eye

The Correspondence Problem

• A different model must be adopted:

The Correspondence Problem

• A different model must be adopted:

Visual system can extract form by matching up individual elements (dots) in an image, computing disparity between them, and finding the most likely surfaces.

Might this involve top-down mechanisms? How could you test that hypothesis?

Next Time: Color Vision

• Read Land Article for Friday