Enhancing Scanned Images

Brief description: This section demonstrates ways of enhancing scanned monochrome images - deskewing, filtering.

Deskewing

When paper is fed through a scanner the direction of the paper often deviates from the orthogonal, therefore the resulting scanned image is skewed, sometimes rather considerably.

The special command - rDeskew is used to deskew an image.

The command works in two modes:

  1. Auto Deskewing - WiseImage automatically estimates the skew value, and then performs the deskew operation.
    Choose Deskew from the rImage menu, and then -Auto.
  2. Manual Deskewing - you can use this mode if the result of Auto Deskewing is not satisfactory. In this mode you can specify a skew angle by drawing a line, which should be horizontal or vertical.
    Choose Deskew from the rImage menu, and then Manual.
    Press the Measure Angle button in the displayed Deskew dialog, and then specify the deskew line with two points. You can use the snap tools during this operation.
Deskew line (manual deskewing)
After deskewing

Filtering Monochrome Images

There are a number of different filters available in WiseImage, which allow you to enhance a scanned monochrome raster image. You can apply filters to the whole image or to any selected fragment. You can also apply filters to several raster images simultaneously.

Using the filters, you can:

  • Remove raster speckles
  • Remove holes (white points in black raster lines)
  • Invert images
  • Smooth raster objects
  • Thin and thicken raster objects
  • Transform filled raster areas to one-pixel contours

All commands for filtering monochrome images are located in the rFilters menu.

Speckle Remover

Choose Speckle Remover from the rFilters menu.

You can specify the size of raster speckles on the screen using the measure buttons of the Speckle Remover dialog.
If Auto Estimating is set to on, WiseImage automatically estimates the speckle size. You can apply the filter several times.
Before applying Speckle Remover
The result of applying Speckle Remover

When applying the filter to an image of very poor quality some data may be lost. To avoid this, you can use the Separation by size operation instead.
See section Separating Monochrome Images by Size for detailed information.

Hole Remover

Choose Hole Remover from the rFilters menu.

You can specify the size of raster speckles on the screen using the buttons of the Hole Remover dialog box. If Auto Estimating is set to on, the program automatically estimates the speckle size.
Before applying Hole Remover
The result of applying Hole Remover

Inversion

Choose Inversion from the rFilters menu.

This filter reverses the color of the monochrome image. After applying this filter the background dots become the image dots and vice versa.
Before applying Inversion
The result of applying Inversion

Smoothing

Choose Smoothing from the rFilters menu.

This filter smoothes raster object outlines, fills edge and inner background droplets, and partially removes raster speckles.
Before applying Smoothing
The result of applying Smoothing
The Smoothing filter is tuned by setting optimal values for the Medianning and Threshold parameters. You can tune and see the results of smoothing in the preview window before applying the filter.

Thinning and Thickening

Choose Thinning (Thickening) from the rFilters menu.

The Thinning filter makes raster objects thinner in the specified directions, by one pixel for one pass. You can specify a number of passes.
Before applying Inversion
The result of applying Inversion

If needed, you have the option of thinning raster objects up to their skeleton - i.e. only pixels in the middle are left.

The Thickening filter makes raster objects thicker in the specified directions. You can specify a number of passes and choose any combination of thickening directions.

Contour (4-coupling and 8- coupling)

Choose Contour from the rFilters menu.

The Contour filter converts filled raster areas to one-pixel contours.
Before applying Contour
The result of applying Contour

Separating Monochrome Images by Size

This operation is effective in the following cases:

  • If you want to prevent small objects from being removed when applying the Speckle Remover filter (e.g., dots in dashed-dotted lines, lines which consist of multiple small fragments, etc).
  • If you need to move objects with a specified size (for example texts) to another raster layer.

The principle of the separation by size operation is similar to speckle removing, except speckles are not removed but transferred to a new raster layer. Any fragments incorrectly transferred to this “speckle” layer can be selected by the user and brought back to the original drawing layer.

Original image

The result of separating to basic and “speckle” layers
The significant elements have been brought back from the “speckle” layer to the basic layer; the “speckle” layer is removed

Autocorrecting Image

Autocorrect runs a set of pre-defined operations.

How to apply autocorrection:

Choose Options from the Tools menu. Go to the WiseImage tab.

  • Specify a set of commands to apply with autocorrection. Close Options.
  • Choose AutoCorrect from the rImage menu.
  • If you have more than one raster image in your document, select the image(s) to apply autocorrection to.

NOTE: WiseImage automatically defines all parameters of the commands included in the autocorrection set (except Rotate). For example, automatic deskewing, removing speckles with automatic estimation of speckle size, etc.

 [ welcome ]   [ hybrid graphics ]   [ quick start ]   [ tutorial ]   [ reference ]   [ about ] 
 
 [ Welcome ]   [ WiseImage for Windows ]   [ WiseImage for AutoCAD ] 

 
top