應用於夜間監控用途的新式紅外線打光器

Abstract

一般夜間監控影像的曝光常有過暗或過亮之問題，使得影像品質遠低於人類 感官可以滿意的範圍。而造成此問題的主因是要取得適當的曝光並不容易，有多 項因素皆會影響曝光如:光源強度、影像感測器的感度、曝光時間長短等等。本論 文由光源強度著手，設計一個能自動改變光源強度的紅外線打光器來改善影像品 質。實作上我們週期性地改變各種紅外線光源強度，以得到多種曝光值的影像， 再從眾多不同曝光值的影像中，挑選出曝光較佳的影像；也可以將各種曝光程度 的影像合成一張更高動態範圍的影像。實驗結果顯示，本論文研製之掃描式紅外 線打光器，利用掃描式週期性變化強度的紅外線光源，加上後續的影像處理，確 實可以有效改善夜間監控的影像品質。

The images captured by surveillance cameras in the nighttime are often too dark or bright so that the image quality can not be satisfactory for human perception. This is because suitable exposure is not easy to be decided. The exposure depends on many factors such as intensity of illumination, sensitivity of image sensors, and exposure time, etc. This thesis is focused on the improvement of the image quality through a new design of IR illuminator. By changing the intensity of IR light periodically, images with different degrees of exposure can be obtained, so that we may choose one well-exposed image or compose an image with increased dynamic range by selecting some well-exposed regions from different exposed images. Experimental results show that by adopting periodically scanning intensity for the proposed IR illuminator, and through proper post-processing of video frames of multiple exposure levels, much improved image quality for night vision can be achieved.