: a) Input image of a sample area of pine, b) binary image 
derived from it by hardclipping, superimposed on the original 
image, c) perimeter of white objects in the binary image, 
superimposed on the original image. 
spruce are reproduced. From a comparison of Fig. 2 and Fig. 3, it 
is obvious that the binary images of a sample area are characteristic 
of the tree species. 
It may be advantageous to enhance the texture of the input image 
prior to hardclipping by spatial high-pass filtering. A sort of high - 
pass filtering can be obtained with the aid of the shade-correction 
unit of the Quantimet which allows to subtract an unsharp version 
of the input image from the original input image. Fig. 4 illustrates 
the effect of this high-pass filtering operation with the shade- 
correction unit. The characteristic texture of this image is seen to 
be drastically enhanced as compared to the texture of the original 
image. However, this method has not been investigated further. The 
following evaluations are based on data from unfiltered images.