本研究發展一套影像擷取系統，透過高速攝影機或網路攝影機連接到個人電腦，準確的擷取主要的震動訊號。原灰階解析度0~255，藉由累加一個小區域的方式增強其解析能力，且在量測物體上貼一畫上黑色線條的白紙，以增強灰階對比。本研究亦使用發光二極體與震動機等兩個實驗，證明影像系統可以正確擷取振動頻率。
光電荷轉換灰階過程中，由於有限的取樣頻率與非線性的現象，而造成訊號中有非物理的頻譜混疊情形。本研究發使用一個簡單的模擬，準確的預測出錯誤的模組，且試著使用幾個方式降低錯誤模組，但無法將其完全排除。文中並運用兩個例子描述，當取樣的臨界頻率小於主要頻率時，其頻譜折疊後的情況。
最後，透過實際量測物體之實驗結果顯示，使用非接觸影像收集低頻訊號是可行的工具。

This study develops an image data acquisition system connecting a high-speed camera or webcam to a notebook or personal computer (PC) for precisely capturing most dominant modes of vibration signal. The motion of the target and camera, the vibration of the camera, and the variation of the light intensity illuminating the target surface are fixed to simplify the factors affecting the image data. Then many difficulties embedded to the system are overcome by the corresponding strategies. First, the original gray-level resolution of a video camera from, for instance, 0 to 256 levels, was enhanced by summing gray-level data of all pixels in a small region around the point of interest. In addition to provide an light source using a car lamp, the image signal was further enhanced by attaching a white paper sheet marked with a black line on the surface of the vibration system in operation to increase the gray-level resolution. The extracted signal may involve the non-physical aliasing modes together with the false harmonics induced by the finite frame rate and non-linear relation for converting the photo-charge of a pixel to the gray level. Using a simple model, frequencies of all the prominent false modes are properly predicted and can then be manually excluded. Two experimental designs, which involve using an LED light source and a vibration exciter, are proposed to demonstrate the performance. Several factors were proven to have the effect of partially suppressing the non-physical modes, but they cannot eliminate them completely. Two examples, the prominent vibration modes of which are less than the associated critical frequencies, are examined to demonstrate the performances of the proposed systems. In general, the experimental data show that the non-contact type image data acquisition systems are potential tools for collecting the low-frequency vibration signal of a system.

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