Application
of
wavelet transform for extracting edges of paddy fields from remotely
sensed
images
International Journal of Remote Sensing, 25-2,
347-357 (2004)
Ishida
T., Itagaki
S., Sasaki Y. and Ando H.
Abstract:
For geographical
information systems (CIS) to be useful in the management of Japanese
paddy fields,
it is vital to be able to prepare base maps that define sections of
field. We
attempted to prepare a base map by detecting the edges of submerged
paddy
fields from a SPOT image with the use of multi-resolution wavelet
transform.
The raw image of SPOT band 3 was decomposed into a low frequency
approximation
image and a set of high frequency detailed images to five levels, and
then
reconstructed. The reconstructed image at the fifth level was obtained
from all
of the high frequency images except for the low frequency approximation
image.
The image reconstructed up to full scale was then applied to a
zero-crossing
scheme and three post-processings -line thinning, removal of isolated
pixels,
and connection of pixels with their neighbours-in order to obtain clear
edges.
The spatial features of the image indicating the edges obtained by
multi-resolution wavelet transform were compared quantitatively with
those obtained
by using a difference of Gaussian (DOG) filter. The multi-resolution
wavelet
transform was better than the DOG filter in that the base map obtained
by the
wavelet transform method represented a 'field block1, which is
typically
composed of 10 holdings of paddy field, more precisely than with the
DOG
filter, and in that the number of open polygons on this map was
smaller,
indicating that the wavelet transform method is more suitable for
producing the
base map in GIS for the management of paddy fields.