You're going to get some noise, but it's best to try and avoid the obnoxious, brightly-colored pixelnoise often associated with digital cameras and extremely long exposures.
这样会增加图像的噪点，但最好还是尝试一下，因为长时间曝光会产生令人讨厌的，明亮的彩色噪点。
2
The second subunit is median filter, which use the median of non-noisepixel in the window to replace the detected noise pixels.
第二部分是中值滤波器，对于检测出的噪声像素，用其相应窗口内的非噪声像素的中值进行替代。
3
Because the target only occupies one pixel, its SNR is low and the target almost be submerged by noise, these all bring huge difficulty to detection.