不同USM锐化参数下图像频谱变化研究

为了研究图像的锐化机理和作用,探讨图像锐化处理对图像频谱成分的影响,通过编程生成12种不同空间频率的正弦波图像,用Photoshop软件将这12种图像组合成一幅完整的灰度图像,作为进行锐化处理的原稿。将原稿图像进行不同参数（数值及半径）的虚光蒙版锐化处理,使用Matlab软件对原稿及经锐化的图像进行二维傅立叶变换（FFT）,随后提取上述12种频率对应的傅立叶谱值,将锐化后的值与原稿对应值相减,对其进行分析和研究。通过对频谱曲线进行比较分析,结果表明：USM锐化对图像的频谱增强作用随USM半径、数值的增大而增大;USM锐化对图像频率成分的增强作用并不均衡;USM半径设置较小而USM数值设置较大时,对图像中高频成分的增强效果较明显;USM半径设置较大而USM数值设置较大时,对图像中低频成分的增强效果较明显;当USM锐化参数（数值、半径）设置都较小时,对图像中高频的部分频谱有减小作用。

Study of Image Frequency Spectrum under Different USM Sharpening Parameters

To study the mechanism and function of sharpening and to investigate its influence on image frequency component, 12 sine-wave images of different spatial frequencies were generated via programming.Then they were composed into a complete gray image,which served as the original image for sharpening.The original image was sharpened with different parameters of USM.The original image and the sharpened images were processed using Fast Fourier Transformation（FFT） method with Matlab software.After that,the corresponding Fourier spectral values of the 12 frequencies were extracted,the corresponding spectral value of original image was subtracted from the values of the sharpened images.The data results were finally analyzed and studied.Through the analysis of the spectrum,it indicated that the USM sharpening effect is stronger, while the USM amount and radius increase.But the effects to the spectral components are not balanced.If the USM radius is smaller but the amount is bigger,the effect to the medium and high frequency components is stronger.The larger the amount of the USM sharpening and the USM radius are,the stronger the emphasis on the low and medium frequency components grows.The medium and higher frequency components are reduced,if the amount and the radius are all smaller.