基于小波变换的大面阵CCD相机影像亮度不一致性消除算法

针对大面阵CCD影像亮度不均匀现象，提出一种基于小波变换的影像亮度不一致性消除算法。在分析像面光照模型的基础上，构造出光照模型的仿真影像，通过分析仿真影像的小波变换系数，发现影像亮度不一致信息集中反映在小波的近似系数之中。利用这一特性，先将数字相机原始影像进行多尺度小波分解，并对近似系数取对数，然后施加一个衰减算子，对近似系数的对数进行非均匀改正，将改正后的系数取指数，再对近似系数进行线性拉伸，同时根据人类视觉系统对不同方向细节敏感度的不同，对不同方向的细节系数进行不同幅度的线性拉伸，以突出图像细节，最后通过影像重建，获得均匀亮度的航空影像。实验结果显示，该算法具有很好的匀光效果，同时能够较好地保持影像细节特征。

Wavelet algorithm for eliminating inconsistent brightness in large plane Array CCD camera images

Aiming at uneven illumination of large plane array CCD images, this paper presents an effective algorithm to extract uneven illumination from images by using wavelet transform. Based on an analysis of the illumination model on a focal plane, emulational images are constructed for the illumination model. Through analysis of the wavelet transform coefficients of emulational images, it is found that information of illumination non-uniformity mainly appears in wavelet approximate coefficients. Taking advantage of this property, the original image is first decomposed with multiresolution wavelet. Next, the natural logarithms of approximate coefficients are calculated, and then an appropriate attenuating operator is applied to implement the non-uniformity correction of approximate coefficients before exponentiating correction coefficients reversely. And different linear operators are applied to detail coefficients of different directions and different scale. Finally, uniform illuminative aerial images are acquired through reconstruction of images after linear contrast-stretch is applied to all the approximate coefficients. The experiments show that the wavelet analysis method can achieve.a satisfying effect of removing the uneven illumination for digital aerial images, and keeping well detail image features.