AdaBoost
AdaBoost selects features from the whole image, from the top left to the bottom right, until it is possible to find a face.
The image below shows examples of features and how the image consists of these features.
At the end, we will have a matrix of numbers from feature selection:
1
2
3
4
5
2 3 5 6
8 9 2 1
0 4 8 7
Each number in the matrix represents "white pixels - black pixels"