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 Заголовок сообщения: Automatic tracing of dotted lines
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Only manual and semiautomatic modes were available for dotted line tracing in Easy Trace till recently. But lines of this type fit for automatic tracing as well. The video demonstrates the method: Dotted line tracing in Easy Trace Pro .

The method consists of the following steps:

1. extraction of a special "dot image";
2. outlining of dots;
3. autodetection of circles in dot contours;
4. transformation of the circles into short strokes;
5. joining of the strokes as line segments regardless their direction.

One may see from the name of the first step that the main its task is to extract an image with well-preserved points. Quality of lines is of no importance. At that:

First, the higher is resolution of the image (DPI), the more point shape resembles circle.

Second, many dots are "glued" to grid lines. So, the grid should be vectorized and then deleted from the image applying the Rasterize Vector Data utility.


Third, the image of black dots should be processed in the following way:

1. "Diffuse" – radius is one half of the average dot radius, factor is 1.5. The operation smoothes dot boundaries and make them more round;

2. "Unsharp Mask" - radius is the average dot radius, factor is up to 1000. The operation separates dots "stuck" to lines and to other each other;

3. "Extraction of Subject Layers" – select admissible brightness range that would finally separate dots from the background.

The second step is automatic outlining. Select "Only without holes" option in the "Save the following contours" field – we don’t need contours of zeros, letters, and other symbols.

The third step is automatic recognition of circles. Remember that superfluous dots are much more "harmful" than omitted. Be careful at selection of diameter range and allowable deviation from roundness.

The fourth step is transformation of circles into strokes 2-3 pix long that enables applying the "Treat lines as points if their length is less than…" option of the Breakup Joining utility.

The fifth step is specifying of joining parameters depending on characteristics of dotted lines. In the rear event that many noise objects are extracted together with dots, Breakup Joining may be subdivided into 2 stages:

1. Joining of most reliable line parts. Specify the search radius a little more than the distance between neighboring points and the angle of line convergence about 140 degrees;

2. Apply the Vector Eraser tool to obvious errors ("false dots, incorrect joining in bottlenecks);

3. Final joining with the search radius equal to 2.5 intervals between points and a negative convergence angle (-20 degrees).


For users of previous ET versions

the following algorithm of dots-to-strokes conversion may be recommended:

1. Extract the dot image with compulsory diffusion and selection of the admissible brightness range to delete numerous irrelevant small objects;

2. Thinning of the black-and-white image. The dots turn into small islands made of 1-5 pix;

3. Apply Mask Filtering (the "Strokes from dots" strategy) to transform the dots into strokes;

4. Automatic Tracing > Autotrace lines;

5. Apply the "Select objects by a query" command of the Group Editor to select and delete all line segments longer than 3 vertices.

Subsequent joining of the strokes into lines agrees with operations described above for up-to-date versions.

The "old" method of dotted line autotracing has some disadvantages yet. Rather large objects may turn into dots at thinning if they are round. In turn, mask filtering makes strokes of ANY pixel conglomerate if it finds room within the 3х3 mask. It results in superfluous points and thus prolongs further editing.


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