S. M. Alex Raj ¹, M. H. Supriya ¹

Affiliations
1 Department of Electronics, Cochin University of Science and Technology, Cochin – 682022, Kerala, IN

Abstract

Background/Motivation: Optical image captured by autonomous underwater vehicles need to be preprocessed as they suffer from various adversary underwater conditions and require low power devices such as FPGA. Methods/ Statistical Analysis: Underwater image degradation due to non uniform illumination is corrected by non linear filtering and is implemented in FPGA. Two dimensional Fast Fourier Transform (FFT) and its inverse along with logarithmic computation were implemented in FPGA as a part of filter implementation. One dimensional row wise and column wise FFT were computed first and then combined to form two dimensional FFT. Findings: FPGA’s can be used for implementing architectures that require high level parallelism such as image processing algorithms due to its inherent parallelism. Frequency based filtering method which is employed for preprocessing an underwater image successfully provided good histogram compared to the original one. Device utilization for implementing structure was estimated. Novel method of FFT implementation, its inverse and logarithmic computation was used in this work. The method can be applied to digital signal processing applications that can be implemented in FPGA. Application/Improvements: Automation of image preprocessing is required in unmanned underwater vehicles used for cable detection, navigation etc. These vehicles are to be provided with low power devices such as FPGAs for long run in underwater applications.

Keywords

Automated Underwater Vehicles, FPGA, Fast Fourier Transform, Nonlinear Filtering, Underwater Image Enhancement

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S. M. Alex Raj ¹, N. Khadeeja ², M. H. Supriya ¹

Affiliations
1 Department of Electronics, Cochin University of Science and Technology, Kochi – 682022, Kerala, IN
2 Department of Electronics and Communication Engineering, Government Engineering College, Trivandrum – 695035, IN

Abstract

Objectives: This paper proposes a novel histogram based image fusion method to refine the visibility of underwater images which are suffered from colour degradation and poor illumination due to ocean depth. Methods/Statistical Analysis: To improve the enhancement of underwater images, R channel is separately processed as red component attenuates heavily compared to blue and green component and is combined with histogram equalized original image. Then various weight maps, suitable for underwater images, were obtained from the single image and are processed before fusion is done. Findings: Automated Underwater Vehicles (AUV) is used for marine navigation, pipeline tracking, video mosaicking etc. Automation of video captured has to be used for various applications where image pre processing is necessary. Hardware implementation helps the automation process to be used in real time scenario. In this work Field Programmable Gate Array implementation (FPGA) of a novel algorithm for the underwater image enhancement is carried out. New weight maps suitable for underwater images were used for fusion as compared to existing methods and were compared with the existing methods. Altiumnano board was used for FPGA implementation. Application/Improvements: Degraded images need to be enhanced before processing it further applications. This work is mainly focussed on underwater images and can be used in AUVs and Remotely Operated Vehicles (ROV).

Keywords

Histogram, Image Fusion, Underwater, AUV, FPGA.

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