The Study Of Color Restoration For Underwater Images

Underwater optical imaging technology has very important relationship with the exploitation of the ocean. The color information, as an key information for properties of underwater objects, can be used to recognize and classify objects by observing their colors and texture. However, due to attenuate of light intensity in different wavelength at different depths traveling in the water, the underwater images became obscure and, especially color loss. Therefore, it is difficult to recognize and classify the objects in water by observing their colors. So, the color correction of underwater images is one issue of great importance for observation of underwater objects.Underwater optical imaging technology mainly include the traditional imaging methods, like photograph, and the methods based on laser, such as laser line scan. This paper, making use of the two imaging methods based on the color science, proposed the color correction method.The first chapter of this paper begins with the research background, followed by the underwater optical imaging technology and their research status at home and abroad.There are two different points of view addressing the image processing. And their research status at home and abroad are showed. Chapter 2 is mainly theory about marine optics, evolution of color science and laser line scanning.Chapter 3 and chapter 4 are the main body. Based on the two optical imaging methods, the capturing images are compensated and corrected. Chapter 3 put forward the color correction based the measurement of white spectrum. The white light absorption spectrum data are measured with the absorption spectrometer at different depth, and then in CIE1931XYZ color system tristimulus values of the spectral datum are calculated. Considering the nonlinear underwater attenuate of light in different wavelength at different depths, based on Beer’ law, the attenuation of tristimulus values are estimated. The images capturing in water were saved and showed (processed) in sRGB which, as a standard color space, was developed on the basis of RGB color space of HDTV. To use the attenuation of tristimulus values, the color space conversion for images from sRGB to CIEXYZ is necessary.And then images were compensated in CIEXYZ color system. Finally, the values corrected in the CIEXYZ was converted to sRGB for display. Meanwhile, except for water absorption and scattering, the CCD of the camera also have nonlinear effects on color loss, the image acquiring system are calibrated by measuring the response curve of the camera.The results demonstrate the feasibility of this method.Chapter 4 is the color correction method based on laser line scanning. The light source is the three line laser, scanning the objects. And CCD collects video, accepting the 3D and color information. Based on the color mixing principle, the wavelength of the three laser is the three-primary colors and white filed is C白. The laser color space is established. Because the different three-primary colors of the laser color space is different from the sRGB, color deviation appears. It is necessary to convert the laser color space to sRGB to correct the color for images. To compensate attenuation of light, the scheme of color compensation and correction is proposed. Firstly, images capturing underwater are compensated using the estimated attenuation coefficient. And then the color correction is carried out. The experiment was carried out in the tank. The water depth is about 20cm. The images were corrected based on color mixing and color space conversion, ignoring the attenuation. The color difference is calculated. Experiments demonstrate that the targets can be 3D reconstructed with true color and texture at millimeter scales.Finally, a summary of the work for the author has done are presented and some suggests of the possible future development in the analysis of color correction.