医学图像处理笔记(3)

Image Convolution

convolution application

Multimedia \Special effects\ photo enhancement\ computer image analysis

convolution calculate step

1. position the center of the kernel at the first pixed of an image and flip the kernel（选择180度）

2. Multiple and sum

3. slide to next pixel

边缘点处理：1. 丢弃边缘 2.边缘插值

小于0为0  ，大于255为255

Image Gradient and Edge detection

An edge is s set of connected pixels the lie on the boundary between two regions

How it comes

Different colors, brightness, textures, material, tissues

Different normal direction of surface

Different illuminance

Edge Category

Gradient

A point is defined as an edge point if its 2-D first or second-order derivativeis greater than a special threshold

gradient can also be interpreted as a complex number with its magnitude determined by:

and the direction determined by:

Roberts

Prewitt

Sobel

Image Noise Reduction

coherence -- incoherence

Gaussian\Median Filter\ open\ close

Gaussian reduction (更好地保持图像原来的属性) standard deviation越大，效果越强，越模糊

Mean Filter（kernel尺寸越大，效果越强，越模糊）

Median Filter（排序去中间值）