Research On The Visual Effect Enhancement Technology For Infrared Images

The technology of infrared thermal imaging plays a more and more important role in the military, civil field and other fields. It has enlarged the range of the human's visual cognition from the visible spectrum zone to the invisible infrared spectrum region. However, the value of the contrast ratio of the infrared image is low, and the visual effects of it are not good. Therefore, the infrared image goes against observation and extraction of scenery's feature. The enhancement of the infrared image for improving its contrast ratio and visual effects has become one important aspect of the current thermal imaging field.The dissertation has studied on the measures of image enhancement and summarized the current approaches. The dissertation has put forward the measure of image enhancement based on the multi-scale directional analysis of the individual image and the fusion of multi-source image. The measure aims to solve the contradiction between the protection of the image's partial detail and the noise filtering.The multi-scale directional analysis is the sparse representation method based on wavelet analysis which has been developed in recent years. The dissertation has applied the multi-scale directional analysis to the de-noise and enhancement treatment of infrared image, and put forward the infrared image enhancement measure which is based on Nonsubsampled Contourlet transform. Taking the advantage of the Nonsubsampled Contourlet transform in the treatment of image's geometrical structure, the infrared image's noise and marginal information can be dealt with separately, therefore, the de-noise can be realized while the image's marginal and detail information has been reserved. Nonsubsampled Contourlet transform has not only inherited the benefits of the multi-scale, multi-directional of the Contourlet transform, but also has the feature of translation invariant. It can reserve the image's marginal information more effectively.In recent years, the application of multi-source image has resulted in the diversity of the image information manifestation. The integration of the multi-source image into one image can meet the requirement of human's visual cognition and is beneficial to the further analysis by the computer. The image fusion technology can integrate the multi-source image about certain concert scenery acquired at the same time or at different time into a new description about the scenery. Infrared and visible light imaging sensor are two different kinds of image sensors with different function and principle. The infrared imaging sensor can detect the invisible thermal radiation, while the visible light sensor can detect the target through the absorbing of the visible light band electromagnetic wave reflected by the target. Through the fusion of the visible light image and the infrared image, we can achieve much better visual effects than those of the individual image enhancement technology.The problem of the image fusion technology merely working in the visual enhancement rests with how to effectively synthesis the visual information in the multi-source image into one image and how to de-noise the source image to enhance the fused image's visual effects. The dissertation combines the multi-scale directional analysis and the multi-source image fusion approaches, and brings forward the image fusion enhancement measures based on the statistical characteristics and the regional features respectively.Considering the existence of sensor's noises, the multi-source image fusion enhancement measure which is based on the statistical model has been put forward. The measure not only more effectively fuses the information of the multi-source image, but also restrains the influence of sensor's noises to the fused image.The judgment of the human's visual system towards the image definition is commonly embodied by the pixels in the region. According to the characteristic of low frequency sub-band and high frequency directional sub-band after the NSCT transform, we designed the image fusion measures based on regional features, which enables the effective reservation of the marginal and detail information while enhancing the fusion image visual effects.According to the infrared and visible image fusion experiments, the image fusion technology aiming at improving the image visual effects can make up for the deficiency of single sensor, improve the use efficiency of image information, therefore, provide a more accurate and comprehensive description towards the target or the scene.The infrared image enhancement measure based on the individual image multi-scale directional analysis and the image enhancement measure based on the multi-source image fusion have their own advantages and disadvantages. The former is aimed at dealing with individual image which has adopted the multi-scale directional analysis in carrying out the frequency domain treatment to de-noise and enhance the marginal and detail information; the later is to fuse the image collected by the multi-source image sensors to acquire the image information which obtains more information than the individual image sensor. The two image enhancement measures apply in different image treatment environment, and both can acquire better effects of enhancement.