Lesson 1. Enhancing Raster Images
Brief
description: During this lesson you will learn ways of enhancing
raster images. Using examples, you’ll find out how to remove speckles
from a raster image, separate an image by size, apply the Smoothing filter,
deskew a scanned image and apply four-point correction.
 See section Enhancing Scanned Images of
the Quick Start guide for detailed information on enhancing
raster images.
Speckle Remover, four-point correction
Choose Open from the File
menu. Open the Sample1.tif file from the Lesson_1
folder.
To enhance the raster image let’s apply the Speckle
Remover filter, then four-point correction to eliminate distortions.
- To remove speckles choose Speckle Remover from
the Filters menu.
Estimate the max speckle size on screen (using the measure tool
 ).
For convenience, use Zoom and Pan
(see the commands of the View menu).
- Click Apply
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Fig.1-1 Original document
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Fig. 1-2 After removing speckles
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- To eliminate distortions choose 4 point Correction from
the Image menu.
Specify the frame size in the Width (265 mm) and
Height (180 mm) fields; choose orientation - Landscape
in the Orientation field.
- Press the Measure Frame
 button
and specify one by one the four corners of the document frame.
- Press OK.
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Fig. 1-3 Specifying 4 frame corners
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Fig. 1-4 After 4-point correction
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Separating by size, deskewing
When applying the Speckle Remover filter,
you can remove small unimportant objects whose size is close to the speckle
size. In this case you can use the operation of separating raster particles
by size. The principle of this operation is similar to speckle removing,
except speckles are not removed but transferred to a new raster image.
Choose Open from the File
menu. Open the Sample2.tif file from the Lesson_1
folder.
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To separate the raster image by size choose Separation
by Size from the Images menu.
Estimate the max speckle size on screen (using the
measure max size tool ).
- Choose a color and (if needed) a name for a new image to which
you want to transfer raster speckles.
- Click Apply.
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Fig.1-5 Original document
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Fig.1-6 After separation
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| In figure 1-6 the centerline fragments that were incorrectly transferred
to the speckle layer, are marked with an arrow. To bring them back
to the original image: |
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- Select fragments that were incorrectly transferred to the speckle
layer - on the Select toolbar, choose the raster data
selection mode (press the Raster Selection
button) and add data mode (press the Add
button). In this example, it’s best to select the raster fragments
with Select Raster Floodfill 
- simply specify with the mouse cursor the particles
to be transferred back to the original layer.
- Choose Merge (Rasterize) from the Modify menu.
- Open the Image Manager (choose Images from the Tools
menu). In the Images dialog, select the image containing
all the speckles and delete it by pressing the Delete
button.
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Fig.1-7 Brining back the important fragments
from the speckle layer
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Fig.1-8 After deskewing
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To deskew the image with automatic definition of the
rotation angle, from the Image menu, choose Deskew
and then Auto.
Smoothing
Choose Open from the File
menu. Open the Sample3.tif file from the Lesson_1
folder.
- Choose the Smoothing filter from the Filters
menu.
- Using the sliders - Medianing & Threshold
- achieve the best results in the preview window
You can change the position of the preview window using the Preview
Area 
buttons of the Preview Dragger dialog, which appears when
starting the filter.
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Fig.1-9 Before applying Smoothing
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Fig.1-10 After applying Smoothing
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