隨著可攜式數位行動裝置的發展，以往只在數位相機上具有的高畫質攝影功能，已經被大量移植到手機和平板電腦上。當今數位攝影裝置的技術功能發展也形成M型化趨勢，專業的單眼或是類單眼相機具備多樣性的可調式功能，諸如光圈大小、曝光時間、測光方式、以及手動對焦等，可供專業使用者依據個人的喜好或構圖所需適當地調整與設定。然而一般使用者並不具備太多專業的攝影知識，且習慣以輕巧好攜帶的手機作為拍攝工具。因此若提供太多相機調整功能，反而對一般使用者造成困擾，此類型用戶期待只要按下快門鍵，就可以輕鬆地拍到品質好的照片，使用者不需花時間了解相機的功能。針對這類型用戶所需的攝影裝置，就須特別加強所謂的「自動」模式。對於相機上的所有設定，我們都必須收集與分析畫面資料，再經由演算法的精心設計，達到可以「自動」幫使用者做適當參數設定。在這些自動處理方法中，自動曝光演算法是最首要的，一張清晰的影像需要曝光適當，過曝或是曝光不足的影像可能讓人難以接受。然而曝光的關鍵即在測光，相對於固定權重式的中央權重、點測光、以及平均測光等，本論文提出一非固定權重式的方法：(1)可依畫面內容的亮暗分布，動態分配權重，達到較佳的曝光成效，使得無論亮暗區域的細節儘可能獲得較好的保留; (2)提出一個可減少影像過曝發生，又儘可能保留住暗部細節的方法。本論文提出的方法相對於上述的固定權重式測光法，能提供較佳的照片清晰度以及對比度。經實驗結果，與中央權重測光法相比，約可以提升1.2~1.3倍影像亮度對比，有效提高影像品質。

With the advance of high end smart phone control functions, the high-resolution and professional photographer functions, that are formerly available only on digital camcorder, have been moved to smart phone and flat-panel computer. In addition, the development of digital camcorder technologies goes to M-type trend, i.e., extremely professional and general purpose design. For the former, examples are single lens reflex (SLR) and SLR-like cameras that provide several adaptable functions, such as aperture setup, exposure time, metering and hand focusing etc, which are designed for professional photographers to capture images according to their preference and skills. However, most users are not that professional in photography and intend to take easy photos by their smart phone. For this general user group, too many camera control functions would puzzle their usage in photography, such that automatic camera control mode is needed. It needs to collect and analyze the characteristics of captured frame to set camera control parameters automatically. Among these camera control parameters, automatic exposure control is the most important. Either over or under exposure will lead to unacceptable captured image quality. The most critical procedure for exposure control is photometry. Instead of adopting aperture photometry or fixed center weighted average metering, we proposed an adaptive weighting procedure for photometry: (1) the image color histogram is utilized to assign weights for exposure, such that either light or dark region details can be reserved; (2) one automatic exposure scheme is proposed to prevent over-exposure while preserving dark region details. As compared to previous exposure control method that adopts non-adaptive photometry, the proposed method can render images with higher contrast and sharpness. Our experiments showed that the brightness contrast can be improved to 1.2~1.3 times higher than that adopts photometry with fixed weightings.

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