Finish the function to extract the channel of color
The Bitmap has three channel used to represented the image.
The three channels are formed by rad, green and blue.
Add button that executes the RGB Extraction
Mer show_result and RGB_extraction
Modify the procedure for reading image
If the image has been read, it will not read the image again. Just use the data in the program.
If the program read the image, the ListBox will focus on the name of the image
Let PictureBox show the result of image
Merge branch 'RGB_extraction'
Add function to handle the process that will show the image on the PictureBox
Addstatic function to translate image to gray level image
Let RGBExtraction be static and can be used by other class (public)
Merge master and RGB_extraction
Let TranslateGrayLevel function can be used by other class (public)
Add button to call the TranslateGrayLevel function and show the result
Merge branch 'translate_to_gray_level'
Let ShowResult function can decide whether it will delete all the result
Modify the behavior  when user click the button that translates the image to gray level image
Create a field of openFileDialog and let it can remember the state of path
Modify the procedure
When user load image or select image, the program will produce a temporary image that is the same as input image and show it on the PictureBox of result
Remove useless code
Finish the thresholding function
This function only supplies the gray level image. It means that when a image will be applied this function, it should be translated to gray level image
Add CheckBox to check whether we want to apply the thresholding function