Lines and other entities of color images can be made of many colors in different shades, so some kind of filtering scheme is needed in order to let the snapping mechanism properly determine the boundaries or raster lines and areas. SuperEdit offers an interactive Raster snap color filter tool that lets the user define and examine adequate color interpretation, before it is used for snapping purposes.

Open the grudz.tif image, a color map that contains some features, like roads and forest areas, suitable for color-sensitive snapping. Choose the Options - Snap colors... option. Enter a point nearby area containing a junction of main roads that drawn in red. The Snap / Trace Colors Filter dialog shows two windows, Colors sample and Filtered image example , that allow for further zooming in and out, if necessary.

In the Colors sample window click those pixels in different shades of red that belong to the main road line. All pixels of the same color get marked by white dots, the counter of Colors in filter increments, and the Filtered image example window shows the filtered image; clicking inside this window toggles between color and black and white presentation. Clicking once more at a selected pixel in the Colors sample window removes its color from the filter; you may also use additional control buttons.

After having a color filter defined, click the OK button to close the Snap / Trace Colors Filter dialog, then choose the Options - Configuration option and select Snap and Magnifying Glass options. Use the Document - Add New Vector option to add empty vector.tvd drawing and to enable the Vector toolbar. Use the Polyline button to draw the polyline along the road. Try snapping to different features, the centerline or intersection of the roads, or the edge of the forest areas.

Scanned grudz.tif is a full color image, so a good filter definition for the main roads may require up to 12 colors. The forest areas drawn in various shades of green, may take more than 20 colors, possibly collected from a number of samples. Needless to say, your snapping results will be only as good as the colors filter’s ability to retrieve a complete image of interesting entities, and only those, from the image. Furthermore, some color images will simply not contain any suitable entities to snap.

Filter colors selections may be saved and loaded when needed again using Save and Load buttons in the Snap / Trace Colors Filter dialog.