Objects--Slides Flashcards
The eye encounters an enourmous variety of complex visual images. Yet, the brain somehow manages to correctly interpret almost every visual image it receives. It is able to correctly identify objects, materials, and surface shapes, as well as shadows and other lighting effects. It does this effortlessly for scenes never encountered before.
Correctly interpreting visual images involvses dealing with one ore more of this difficult general problems (plus finamental biological constraings).
Context Problem
Underlying oure remarkable ability to interpret images is a set of sophisticated grouping mechanisms, that try to link together image features that arise from the same physical source. To understand why grouping mechanisms are essential, it is useful to consider the context problem the visual brain must over come.
Objects often appear in a complex and varying context of other objects.
What is the solution to context problems?
First measure attributes of hte images in small regions.
Second, combine the small regions into wholes using rules that are related to the physical laws and statistical facts of nature and to past experiences.
Erasing the bottom half of the abstract object reveals the recognizable object. Why are we unable to recognize the square-root 16? the context of other contours causes us to group the countour elements in a way that prevents the square-root of 16 from making contact with our stored memorey for that object. The implications is that proper grouping is essential for project recognition.
Any way of marking word boundaries helps the recognition process.
Screech Owls
Screech owls have feathers that match the features (brak) of oak tress (the trees they frequently inhabit). If their features ccannot be grouped seprately from the background, they are more difficult to recognize.
Other examples of camoflauge.
Proximity
Gestalt grouping principle.
Objects that are nearby tend to be grouped together.
Similarity:
Gestalt grouping principle.
Objects that are similar tend to be grouped together.
Good Continuation
countour elements that are consistent with a smooth contour tend to be grouped together.
Gestalt grouping Principle
Closure
Gestalt Grouping Principle
Countours that are consisted with a closed form tend to be grouped together.
Gestalt grouping principles: “proximity” (position) and various possible dimensions of similairity.
The Gestalt principle of “good continuation” contour elements that are consistent with a smooth curve tend to be grouped together.
Good Continuation…
Because of good continuation, the two straight line segments in A tned to look like a pair of crossing “sticks” Because of the closure of the same two line segments tend to be split at the middle to become parts of two “butterfly wings”
Example of using simple feature dection followed by a gestalt grouping rules to gorm groups in a novel texture pattern.
Left to right: input image –> perform feature/primitive detection like V1 –> use cood-continuation, proximity, etc. to form small groups –> use shape similarity (comparing or matching shapes) to form larger groups from small groups.
Perceptual grouping also makes use of principles that are based upon the three-dimensional properties of the environment. For example, these line segments are grouped into two boxes and a cylinder. Object corners occluding a background object tend to form an “L junction” or an “Arrow Junction.” Object corners that do not occlude a background object tend to form a “Y junction.” Occluded contours of an object tend to form “T junctions” with the contours of the occluding object. These principles, plus the Gestalt principles, are used to group features into wholes that are likely to correspond to physically sepearate objects.