Geoscience Reference
In-Depth Information
processing applications.
We next rectify the image, i.e., we correct the image distortion by
transforming it to a rectangular coordinate system using a script that is
similar to that used for georeferencing satellite images in Section 8.5. h is
we achieve by dei ning four points within the image, which are actually at the
corners of a rectangular area (which is our reference area). We i rst dei ne the
upper let
,
lower let
,
upper right
, and
lower right
corners of the reference area,
and then press return. Note that it is important to pick the coordinates of the
corners in this particular order. In this instance we use the original image
I1
, but we could also use any other enhanced version of the image from the
previous exercises. As an example we can click the let side of the ruler at 1.5
cm and at 4.5 cm, where two thin white sediment layers cross the ruler, for
use as the upper-let and lower-let corners. We then choose the upper-right
and lower-right corners, further to the right of the ruler but also lying on the
same two white sediment layers,
imshow(I1)
basepoints = ginput
and click return which yields
basepoints =
517.0644 508.9059
511.5396 733.5792
863.2822 519.9554
859.5990 739.1040
or any similar values. h e image and the reference points are then displayed
in the same i gure window.
close all
imshow(I1)
hold on
line(basepoints(:,1),basepoints(:,2),...
'LineStyle','none',...
'Marker','+',...
'MarkerSize',48,...
'Color','b')
hold off
We arbitrarily choose new coordinates for the four reference points, which
are now on the corners of a rectangle. To preserve the aspect ratio of the
image, we select numbers that are the means of the dif erences between the
x
- and
y
-values of the reference points in
basepoints
.
dx = (basepoints(3,1)+basepoints(4,1))/2- ...
(basepoints(1,1)+basepoints(2,1))/2
