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These mean greyscale pixel values for the image were 111.711 for the red channel,<br />
136.542 for the green and 102.636 for the blue. This meant an average deviation<br />
of 22% in the blue channel for areas of roof (average mean for the roof samples of<br />
130.776 compared to 102.636 for the entire image). In terms of automated image<br />
analysis the variation could help develop a control by training a key against the<br />
known building values.<br />
Figure 14: Blue colour band pixel count for study area<br />
Histogram of mean blue channel pixel values for the c quadrant of ordnance<br />
survey sheet # 3012 –building polygons in this are were found to vary by 20%,<br />
indicating that this variation has the potential to form part of a training algorithm<br />
used in the development of a key for automated image analysis.<br />
It should be noted that image quality and the degree of shade and light can vary<br />
according to the environmental variations present when the image was captured.<br />
This study is not concerned with determining an exact value for the capture of<br />
buildings but is instead looking for variations from the mean values in the entire<br />
image. The aim is to gather enough unique deviations (such as the variance found<br />
in the blue channel above) to narrow the remaining values into categories.<br />
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