【 Gray scale 】 Generally, other image processing is based on the grayscale ， so
before handling, you can do a grayscale processing, then click button【Apply to source】。
For the grayscale than the color image occupied smaller memory，for large image step by
step handle, to a certain extent to avoid the lack of memory.
For color image, adjust contrast and brightness, have some auxiliary effect to
following dither processing.
Adjust contrast:
Invert:
Before processing
After processing
Sharp:
Before processing
After processing
