Before the OCR is applied the cropped image, Top-Hat
Filtering is applied to reconstruct the image because that the
cropped image sign is small in dimensions and may contain dirt
or blur that may adversely influence the OCR recognition[5].
Then, a Median Filter of window size 3×3 is applied to reduce
the noise on the image. After the OCR recognition, the result
is further validated by examining whether the recognized sign
is a valid runway number. The valid runway number can only
be from 00-36 since the number corresponds to the magnetic
heading of the runway.