matlab图像预处理，包括灰度化，对数变换，直方图均衡化，线性平滑滤波，中值滤波，自适应滤波，图像锐化，图像二值化，各类边缘检测算子-matlab image preprocessing, including gray-scale and logarithmic transformation, histogram equalization, linear filtering, median filtering, adaptive filtering, image sharpening, ima