Exercise S9: Using Bitonal Filters and Editing Tools

In this exercise you use bitonal filters to improve raster line work and use raster editing tools to remove unwanted spots from an image.

• Bitonal filters improve the appearance of raster line work in a bitonal image, often eliminating the need for redrawing.
• Raster editing tools allow defects and scanning artifacts to be removed from the image.

In this exercise, you improve existing line work by applying a line thickening filter to a portion of the drawing. You also use the raster Remove tool to remove unwanted raster pixels from the drawing.

Related Exercise

• Exercise S2: Cleaning Up Images Using Despeckle

Before doing this exercise, ensure that AutoCAD Raster Design toolset options are set as described in the exercise Exercise A1: Setting AutoCAD Raster Design Toolset Options.

Exercise

1. In the \Tutorial2 folder, open the drawing file Scanned_06.dwg.

   Clean up jagged line work

2. Click View menu Named Views. Set the current view to TU-pad.

   Some of the raster lines are very thin. Some lines, such as the dimension lines, have gaps due to poor scanning quality.

3. Click Raster menu Image ProcessingBitonal Filters. Then (as noted on the command line) press Enter to select the whole image.
4. In the Bitonal Filters dialog box, select Thicken for the filter type, and enter 2 for the number of passes. Verify that all directions are checked, then click OK.

   After you thicken the lines twice, some closely spaced parallel lines have merged into a single line.

   

   Undo the Bitonal Filter Thicken command

5. Enter u to undo the Thicken command.
6. Click Raster menu Image ProcessingBitonal Filters. Then press Enter to select the whole image.
7. Again select Thicken for the filter type, but select 1 for the number of passes, then click OK.

   With one pass, the gaps in dimension lines are repaired, but the closely spaced lines remain separate. Some experimentation and iteration is often necessary to achieve optimum results with filters.

   
8. Click View menu Named Views. Set the current view to TU_extents.

   AutoCAD Raster Design toolset has applied the thickening filter to the entire image.

9. Use PAN and ZOOM to examine the line work in the image.

   Remove spots

10. Click View menu Named Views. Set the current view to TU_spots.

    This area of the image contains spots (scanning artifacts) from small holes in the original drawing.

11. Click Raster menu RemoveCircular Region.
12. Click the middle of a spot for the center point, then click a second point to mark the radius of the circular area to be removed.
13. Press Enter to repeat the command and draw a circle to remove another artifact.
14. Close the drawing without saving changes.