Steps Taken to Produce Map with Area Estimates

Although Idrisi32 is a powerful GIS program, it does not allow the user to select portions of an image in a non-linear fashion. Whereas PSP provides the user with a draw tool and a freehand selection tool. So I used PSP to select the wetland pool that contained cattails and water. I applied a green filter to that portion of the image. This had the effect of diminishing the red values of the water to near zero. Then I applied a red filter to the upland portion of the image. This elevated the red values for all of that selected area to a level above 240. I continually scanned across the image with the eyedropper tool to review the changes in the RGB levels until I adjusted the opacity of the filters to produce the desired separation.

Then I used the command color > split channel > split RGB.This produced red, green and blue layers or channels in grey scale. These were then saved as individual images. This approach converted the pixels to single values rather than three-level RGB values. Both the red and blue images provided reasonable separation but red was superior in this particular image.

The red image was converted from a JPEG file to a bitmap file because it is easier to import bitmaps into Idrisi32.

Detail of  steps needed to develop delineated map with area determinations

Step 1. In Paint Shop Pro™  I drew the border of the wetland area with freehand selection tool and smart edge feature.

Step 2. I filled that selection with green (0,255,0) to an opacity level in which water has a red value near zero. In this case 85% opacity.

next page