適用於影像放大之邊緣強化技術

Abstract

數位影像目前被廣泛應用在生活中的各個領域，例如電子書、高畫質數位電視、平板電腦、智慧型手機，數位相機等應用，另外，由於面板顯示技術不斷創新，顯示解析度越來越高，於是需將原始的低解析度數位影像進行放大的動作。將數位影像放大後，普遍存在的問題是影像放大完後會有影像失真問題，例如鋸齒效應及影像邊緣模糊的現象，降低影像的觀看品質，因此影像放大後的品質提升是很重要的課題。 本研究將針對上述現象，提出方法來克服放大後的影像邊緣鋸齒化和模糊的效應，對於放大後影像色彩的平滑度、對比度改善，我們提出兩個階段來改善放大後的影像邊緣特性與品質： 第一個階段是放大前的影像前處理，透過尋找邊緣，針對邊緣處做初階強化處理， 接著利用邊緣偵測方法，分別找出低解析度影像中邊緣的強、弱資訊，根據這些資訊及放大倍數比例來調整立方內插時所要參考之像素點距離，以內插出較好的影像放大效果。第二個階段是放大後的影像後處理，首先利用對比擴展法來拉開影像之對比度，調高相鄰像素之間的對比，接著參考邊緣資訊，利用可調整銳化係數之空間銳化濾波器來作為我們影像強化的方法，完成影像邊緣處的強化處理，使人眼在視覺上能夠感知到更多的影像細節紋理；針對影像邊緣鋸齒狀的部份，利用兩種邊緣平滑化的方式來對影像放大後的邊緣鋸齒狀做處理與修飾。 最後，經由主觀的人眼判斷和客觀的模擬實驗結果可以顯示出使用上 述兩個階段的影像處理後，可以提高放大後的影像品質。

Digital image has been widely used in all kinds of fields in our life; for example, eBook, HDTV, tablet PC, smart phones, and digital cameras. Moreover, the display technology is innovating and the resolution is higher, so the low resolution digital image will need to be magnified. After magnifying the digital images, the common problem is the distortion problem, such as jagging effect and blurring that will lower the viewing quality. Therefore, how to increase the quality after magnifying the image is an important issue. Aiming on the above mention phenomenon, this research proposed some methods to overcome the jagging and blurring effect. As to the color smoothness and the improvement of the contract ratio after magnifying, we proposed a two-phase method to improve the edge characteristic and quality: The first phase is the pre-disposal of the image before magnifying. By searching for the edges and make initial enhancement then using edge detection to look for the strong and weak information in the edge of low resolution images. This information and the magnification ratio are used to adjust the referenced pixel distances for cubic interpolation so as to interpolate better magnified image. The second phase is the post-disposal of the images after magnifying. First use the contract stretching method to pull apart the contract ratio of the images and increase the contract among pixels. Then, use the reference for the edge information and the sharpness filter, which can adjust sharpness factors, as a method to strengthen the images and complete the edge strengthening treatment. That is to allow human eyes to sense more image details. Regarding to the jagging edge, use two methods of the edge smoothing to handle and modify the jagging effect after magnifying. Finally, subjective human eyes judgment and objective simulation experiment results showed that after the above two-phase approach, the magnifying image quality can be increased.