本文研究使用數位相機拍攝之影像，反向推定投射在一反射屏幕上之光域的照度分佈。為了應用數位相機掘取二維影像的能力，相機所拍攝的影像，是透過光源投射在某一顯像平面的，所產生的光跡分佈圖。

　　使用相機讀取此種光跡分佈有因相機取得影像時所發生的問題：入射光太亮造成反射光度飽和、太暗無法產生反射光、及反射光度與相機成像之灰階值是非線性關係等三種特性，又一般商用數位相機本身的灰階成像，也只有256 個灰階值的有限解析度。為了克服上述4 種限制對數據精確度的負面影響，本文改變投射光源的電源之電壓，攝得數張影像，將這些影像疊合成一張解析度高於256 個灰階刻度的光跡分佈圖。本文先用光電管量取照度和相機讀取其在反射面之成像的灰階值，以得到入射光與成像灰階值的關係。其次應用二維疊代式濾波器移除高頻的雜訊後，得到平滑且高解析度的影像圖。假設不同電源電壓不會影響相對的光跡分佈圖，切除最高和最低灰階值之像素後，將數張影像之灰階與光度數據用最小平方誤差法，疊合成同一張影像。本文應用數個實例，顯示直接量取光源在反射面的光跡誤差約可得到5%以下光流明之絕對誤差的精確度。

　The gray level distribution of an photo frame taken by a digital camera from the image on a screen, which is generated by an incident light source projecting on the screen, is employed to calculate the light intensity. distribution on the screen. The relation between the light intensity and the gray level on the screen is obtained by experiment. Since there is significantly large noise on an image, the iterative filter basing on the Gaussian smoothing
is employed to remove the noise and preserves the mean information. If the light intensity of the incident ray is larger than a certain value, the gray level of the resulting frame shows a saturated response. In order to overcome this　difficulty, several frames are taken by varying the voltage of the light source so that some are unsaturated and others have saturated situation. The least squares method is employed to combine these frames into a single frame. The numerical tests show that the proposed numerical scheme has an acceptable error during the combination procedure.

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