Adopt adjust_gamma from skimage and reduce dependencies

[hejm37]

No description provided.

[codecov]

Codecov Report

Merging #112 into master will increase coverage by 0.00%.
The diff coverage is 84.21%.

@@           Coverage Diff           @@
##           master     #112   +/-   ##
=======================================
  Coverage   82.24%   82.24%           
=======================================
  Files         143      143           
  Lines        6500     6517   +17     
  Branches      967      971    +4     
=======================================
+ Hits         5346     5360   +14     
- Misses       1059     1060    +1     
- Partials       95       97    +2     

Flag	Coverage Δ
#unittests	82.24% <84.21%> (+<0.01%)	⬆️

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Impacted Files	Coverage Δ
mmedit/datasets/pipelines/utils.py	92.85% <83.33%> (-7.15%)	⬇️
mmedit/datasets/pipelines/matting_aug.py	95.11% <100.00%> (-0.03%)	⬇️

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