Underwater Image Enhancement by Rayleigh Stretching in Time and Frequency Domain
| Autor: | Peng, Yu-Ting, 彭煜庭 |
|---|---|
| Rok vydání: | 2019 |
| Druh dokumentu: | 學位論文 ; thesis |
| Popis: | 107 Light scattering and color shift are the main reasons to cause the underwater images distortion when the visible light propagates in the underwater. Scattering effect is brought by the suspended particles in the water that reflect the light in the other direction, it lowers visibility and contrast for the underwater images. The phenomenon of color shift is the presentation of blue or green due to the attenuation of the energy of different wavelengths when the light travels in the underwater. This thesis proposes a Rayleigh stretching-based method in the time and frequency domain to restore the underwater images. The method includes a few steps such as background color correction, Rayleigh stretching in time domain, Discrete Wavelet Transform (DWT) with Contrast Limited Adaptive Histogram Equalization (CLAHE) to enhance the features, contrast adjustment, and sharpening the edges. Through the enhancement switching in the time and frequency domain, it can lower the impacts of noise and keep more information of underwater images. Experimental results through both the qualitative and quantitative analyses with the simulated underwater images and natural underwater images demonstrate that our approach greatly improves visibility and contrast, and obtains best values in terms of entropy, underwater image quality measure (UIQM) and feature similarity (FSIM), respectively. |
| Databáze: | Networked Digital Library of Theses & Dissertations |
| Externí odkaz: |
|