Developing the Demosaicing

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Developing the Demosaicing Algorithm
in GPGPU
Ping Xiang Electrical engineering and computer
science
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Outline
Background Algorithm Implementation Experiment
Results Future Work
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Background

• Color Filter Array.
• A mosaic of color filters in front of the
  image sensor

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Background

• Demosaicing algorithm is to reconstruct a full
  color image
• from the data collected by the color filtering
  array.

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Algorithm

• Bilinear interpolation
• The red value of a non-red pixel is computed by
  the
• average of the two or four adjacent red pixels,
  and
• similarly for blue and green.

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Algorithm
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Algorithm
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Algorithm
For Green Channels
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Algorithm
For Red or Blue Channels
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Implementation
Optimization 1. Vectorize the pixel data to be
processed 2. use shared
memory to reduce the data transfer
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Implementation
1. Vectorize the pixel data to be processed
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Implementation
2. Use shared memory to reduce the data transfer
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Experiment Results
Platform ATI Radeon HD 4870
Brook 1.4 Nvidia GeForce 8800
GTX CUDA 2.1 Dual Core AMD
Opteron(tm) 2212 Frequency 2.0GHz
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Experiment Results
For small data size, GPU is not always a good
choice a. Memory transfer time dominates
the kernel execution time b. Computation is
not that complex enough
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Experiment Results
When the data size is small, CUDA has better
performance. When the data size increases to
4K, the brook performance catches up with
CUDA
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Experiment Results
Explanation ?

Memory Speed Memory Speed Stream processing Units Stream processing Units Stream processing Units
HD 4870 800 85102
GTX 8800 GTX 8800 128 (168)

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Experiment Results
Shared Register Usage
Read data into shared register and try to reuse
the data
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Experiment Results
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Future Work
1. Shared memory usage for further optimization
2. Integrate the code with proper interface to
import image data and export pixel data
3. Report
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Reference
1. High-Quality linear interpolation for
Demosaicing of Bayer-patterned color images,
Henrique S. Malvar, Li-wei He, and Ross Cutler
2. An Improved Demosaicing Algorithm Alexey
Lukin, Denis Kubasov
Questions?