First of all, the outboard black area was treated by fixing its gray value similar to the inboard tint area, thus the back ground was consistent wit tint area, then according to its gray character, the background was wiped off.

• 首先将外层黑色区域的灰度值设定为与内层浅色背景区域相近；这样原指纹图像的背景即变成比较均匀的浅色区域；然后根据其灰度特性将其去除.