四、分析题（3小题，每题10分） Figure16
5 19、 以下为JPEG 的顺序编码的原理框图，回答以下问题： （1） 解释各个环节（框图）的作用；（5分） 答：
FDCT ：离散余弦变换，将空域表示的图像转化成频域形式，信号能量集中于低频；（2分）
量化器：对前一环节的DCT 系数归类并编码（通过量化表）；（2分） 熵编码器：对量化的结果进行统计编码（变长编码）；一般在其之前先进行游程编码。（2分）
（2） 为什么引入量化器，指出其对编码有何影响？（5分） 答：
引入量化器可以有效减少DCT 非零系数的数目，（2分） 但会造成高频成分的丢失（图像纹理细节的失真）（2分）
20、 Figures shown in (18-1 and (18-2 are two types of smoothing filter mask of image enhancement in spatial domain. (18-1 is called ‘Neighborhood- averaging mask’, its frequency response shown in (18-3; (18- 2 is called ‘ Weighted-averaging mask’, and its frequency response shown in Figure20-4. a. Which mask has better ability for image smoothing?(5 points 答：加权邻域平均模板性能更好； （4 分） b. Please analyze
their smoothing effects in frequency domain.(5 points 答：邻域平均模板的频响：由频响图可看出高频阻带不平滑，有 旁瓣。 加权邻域平均模板的频响：频响图高频阻带平滑衰减，无旁瓣， 滚降特性 j 较好，故低通（高阻）性能较前者好。 （6 分） bb 0 1/5 0 1/5 1/5 1/5 0 1/5 0 1/10 1/10 1/10 1/10 1/10 1/10 1/10 1/5 1/10 18-1 Neighborhood-averaging mask 18-2 Weighted-averaging mask 18-3 Frequency response of 6 18-4 Frequency response of Neighborhood-averaging mask(cross Weighted-averaging mask(cross
19 、A telescope in an orbiting observatory is used to produce images on a high-resolution CCD array. It has been found that the images are a little blurry due to optical effects in the telescope. You have been called in as an image processing expert to devise a method to sharpen the digital images. Describe how you would go about solving the problem, given that the only images you can obtain are of astronomical objects. You cannot modify the telescope in any way. The only option is to process the digital images.(10 points 答：1 、用逆滤波复原图像、要求给出具体的方法（eg. Wiener filter or others） . (5分 2） 、锐化（举出空域或频域的方法之一即可） 7
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