implementing gist on the gpu. refrence original work aude oliva, antonio torralba modeling the...
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ImplementingGIST
on the GPU
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Refrence
• Original Work Aude Oliva, Antonio Torralba Modeling the shape of the scene: a holistic
representation of the spatial envelope International Journal of Computer Vision, Vol.
42(3): 145-175, 2001. CPU Implementation http://cvcl.mit.edu/Papers/IJCV01-Oliva-
Torralba.pdf
• Our Work Parallelize to work on the GPU
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Introduction
• Recognition of real world scenes
• Spatial Envelope A very low dimensional representation of the
scene is called the Spatial Envelope. Takes care of
• Naturalness • Openness• Roughness• Expansion• Ruggedness
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Intuitive Notion
• Naturalness Straight lines indicate man made structures Crooked , rough lies indicate natural
environment.
• Openness Presence of horizon reflects highly open
environment
• Roughness Refers to the size of its major components. Is correlated with the fractal dimension of the
scene
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Intuitive Notion contd…
• Degree of Expansion Converging parallel lines allows to percept depth
gradient of the space. A flat view of a building would have a low DoE A street with long vanishing lines would have a high
DoE.
• Degree of Ruggedness The deviation of the ground wrt horizon Open environments have a flat horizontal ground
level Mountainous landscapes have rugged ground Ruggedness produce oblique contours, hide the
horizon. Man-made environments built on flat ground, less
rugged.
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Basic Algorithm
• Create Gabor Filter Bank
• Preprocess image Local contrast normalization Local luminance invariance normalization for
color images
• Descriptor Convolve image with filters For each filter
• Divide image into blocks• Mean of each block is a number in feature vector
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Parameters Involved
• Number of Scales Typically = 3
• Number of orientations per scale Typically = 8
• Image size Typically 320x240 to 1024x1024
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Ways to Parallelize
• On Number of scales * orientations per scale Number of threads = 24 Less than typical image size
• On ImageMxN Pixels Number of threads = M*N >> 24. High degree of parallelism.
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Parallelization for creation of Gabor filter
• Pixel Level
Threads calculating Gabor filter value
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Parallelization for prefiltering image
• Pixel Level
• Fast Fourier Transforms
• Pixel by pixel Multiplications
=> Inherent Parallelism
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RGB image components Filters
Descriptor
Division into blocks
Calculating Descriptor
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64 128 256 512 1024
0
10000
20000
30000
40000
50000
60000
70000
CPUGPU ( Old )GPU ( New )
Graphs
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Speed up
Image Size CPU Time ( ms ) GPU Time ( ms )
64 x 64 250 350 300
128 x 128 750 450 300
256 x 256 3140 800 400
512 x 512 12200 2100 550
1024 x 1024 65500 5100 1200
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Thank You !!