model comparison and challenges ii compositional bias of salient object detection benchmarking...
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Model comparison and challenges II
Compositional bias of salient object detection benchmarking
Xiaodi HouK-Lab, Computation and Neural Systems
California Institute of Technology
for the Crash Course on Visual Saliency Modeling:Behavioral Findings and Computational Models
CVPR 2013
Schedule
On detecting salient objects• Learning to Detect A Salient Object [Liu et. al., CVPR 07]• Frequency-tuned Salient Region Detection [Achanta et. al., CVPR 09]
The progress!• Some top performers:
– [PCA] What makes a patch distinct [Margolin et. al., CVPR 13]– [SF]Saliency filters [Perazzi et. al., CVPR 12]:
• F-Measure: 0.84
– [GC]/[GC-seg]Global contrast-based salient region detection [Cheng et. al., CVPR 11]• F-Measure: 0.75
– [FT] Frequency Tuned Salient Region Detection [Achanta et. a.l., CVPR 09] :• 0.65 by [Achanta et. al., CVPR 09].
Image from [Perazzi et. al., CVPR 2012]
The progress?• Salient objects in PASCAL
VOC?– 850 images from VOC 2013
validation set.– Intersection of main challenge
and segmentation challenge.– Answers more questions:• Where is your algorithm (in
salient object detection)?• Where is salient object detection
(in computer vision).
The progress
• FT: 0.28• GC: 0.39• SF: 0.35• PCA: 0.40• GC-seg: 0.38
55%
performance
drop!!
The arguments
• No!!These objects are not salient!
• Our algorithm works on images with salient objects only!
The paradox of salient object detection
But hey, what is a “salient object”?
COMPOSITIONAL BIAS
Before we proceed…
• Google Image Search: “science”– Rutherford atomic model (9)– Test tubes (10)– Microscopes (4)– Double helix (3)– Old guys with crazy hair and glasses (3)
Stereotypes of science are not sciences!
How to compose a biased salient object detection dataset
Decide to build a new salient object dataset!
So what is saliency?
Searching for unambiguous examples of saliency…
Found one! Add to my dataset!
Job done! Let other people play with my
dataset!
The compositional bias
• Compositional bias: Biases introduced during the composition of a dataset:– Exaggerating on stereotypical attributes.• Limited variability in positive samples.• Lack of negative samples at all.
Unlike datasets in machine learning, where the dataset is the world, computer vision datasets are supposed to be a representation of the world.
---- [Torralba and Efros: Unbiased look at Dataset bias]
Compositional bias: the statistics
• Object number
Compositional bias: the statistics
• Object eccentricity
Compositional bias: the statistics• Global foreground and background contrast
Compositional bias: the statistics• Local foreground/background contrast (contour strength)
TOWARDS A BETTER SALIENT OBJECT DATASET
The new project
• Build a salient object detection dataset from a good object detection dataset (e.g. PASCAL VOC).
Let the eye fixations pick up those salient objects!
Data collection (in process)
• SR Research EyeLink 1000• 2-sec viewing time.• “Free-viewing” instruction (will mention it
later).• 3 subjects (more subjects on the way).
We will release the dataset very soon!
What makes an object salient
• Unit conversion:– From fixation maps– To object fixation score• sum of blurred fixation map intensity within the object
mask.
Object size and saliency
• Large objects attract more fixations.
• Small objects receive denser fixations.
Object size and saliency
Objects, salient objects, and the most salient objects
• Salient objects:– Fixation score higher than
mean (67.3% objects).• Most salient objects:– Fixation score higher than
mean*2 (27.8% objects).
Image with fixation Object labeling Salient objects Most salient object(s)
Salient objects and salient object detection
• Guess how does the algorithms perform on “salient objects” and “most salient objects”?
On all objects:• FT: 0.28• GC: 0.39• SF: 0.35• PC: 0.38
Testing on salient objects
Salient objects on PASCAL VOC
60%
performance
drop!!
• FT: 0.22• GC: 0.35• SF: 0.31• PCA: 0.38• GC-seg: 0.39
Testing on most salient objects
Most salient objects on PASCAL VOC
• FT: 0.10• GC: 0.20• SF: 0.15• PCA: 0.26• GC-seg: 0.23
79.8%
performance
drop!!
Something is wrong, seriously!
DISCUSSIONS
The role of saliency in a visual system
• Bad performance because of boundary detection?
• Bad performance because of unpredictability of human “free will”?
Saliency as an oracle
• Oracle selecting the best segment– CPMC: 78% from 154 segments– gPB: 61% from 1286 segments
* coverage = intersect/union
Saliency and tasks
• Build a salient object detection dataset from an egocentric object dataset.
• Let the eye-fixation speaks
Eye TrackerForward-looking Camera
Learning to recognize daily actions using gaze, [Fathi et. al. ECCV 12]
What makes an object salient?Task
ObjectSaliency
• Object in egocentric actions• Fixated object ==
Manipulated object?
THANKS
Acknowledgement
• Joint work with Yin Li @ Gatech.
• Special thanks to Nathan Faivre for his kind help on eye tracking.
Open discussions
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