Instruct: Identify the main and secondary category of Arxiv papers based on the titles
Query: Sky pixel detection in outdoor imagery using an adaptive algorithm and
  machine learning
12
The categories of this paper are: nucl-th
22
The categories of this paper are: chao-dyn
2
The categories of this paper are: math
31
The categories of this paper are: ao-sci
14
The categories of this paper are: math-ph
35
The categories of this paper are: mtrl-th
5
The categories of this paper are: gr-qc
13
The categories of this paper are: quant-ph
18
The categories of this paper are: econ
32
The categories of this paper are: atom-ph
30
The categories of this paper are: q-alg
33
The categories of this paper are: plasm-ph
16
The categories of this paper are: stat
20
The categories of this paper are: acc-phys
15
The categories of this paper are: nucl-ex
24
The categories of this paper are: dg-ga