1 角度矫正

https://blog.csdn.net/weixin_39133209/article/details/127754001
https://zhuanlan.zhihu.com/p/370145715
https://blog.csdn.net/m_buddy/article/details/81463234
https://blog.csdn.net/weixin_42869334/article/details/123348328
https://www.codenong.com/jse94242f6bee9/
http://t.zoukankan.com/Bearoom-p-12489396.html
https://jishuin.proginn.com/p/763bfbd6aa7d
https://blog.csdn.net/m0_37382341/article/details/104971942
https://blog.csdn.net/wzw12315/article/details/105676529

2 畸形矫正

https://blog.csdn.net/qq_19270967/article/details/106472214
https://zhuanlan.zhihu.com/p/370145715
Document rectification and illumination correction using a patch-based CNN
Doctr: Document image transformer for geometric unwarping and illumination correction

3 深阴影遮挡文本

https://blog.csdn.net/search_129_hr/article/details/127764142
https://zhuanlan.zhihu.com/p/427522496
https://blog.csdn.net/weixin_46548255/article/details/124233248
https://www.jb51.net/article/204840.htm

4 文字与背景的对比度低

https://blog.csdn.net/kl1411/article/details/121907675
https://blog.csdn.net/lk3437456/article/details/109906244
https://blog.csdn.net/molihong28/article/details/89244326
https://blog.csdn.net/u011473939/article/details/30513443
http://ddrv.cn/a/709869
https://zhuanlan.zhihu.com/p/437630873