Vectorize Image

Click the Image | Vectorize Image command or click the  button to open the Vectorize Image dialog. The Vectorize Image dialog controls the settings that automatically convert an image into a vectorized data set. A complete image can be vectorized, select colors on the image can be vectorized, noise can be removed, polygons or polylines created, and a number of other image processing options are available.

 

Set the colors to vectorize and the edge detection options in the Vectorize Image dialog.

 

Vectorization Scheme

The Vectorization Scheme saves the settings for different vectorization types to use again on similar images, without resetting or remembering all the parameters. To change the Vectorization Scheme, click on the down arrow next to the current scheme name and select the desired scheme from the list.

 

To create a new Vectorization Scheme, set all of the parameters in the dialog. Type a name in the Vectorization Scheme box. Click Save to the right of the scheme name to store the scheme to a file.

 

To delete an existing Vectorization Scheme, click on the down arrow next to the current scheme name. Select the desired scheme from the list. Click Delete to the right of the scheme name and Save button.

  

Colors to Vectorize

Didger gives you the option to vectorize an entire image or specific colors or color ranges from the image. To vectorize the entire image, select the Complete Image option in the Colors to Vectorize section. To vectorize only certain colors or ranges of colors, select Selected Colors in the Colors to Vectorize section. For example, you may only want to vectorize the blue rivers on a contour map.

 

To set specific colors, select the Selected Colors option. Move the cursor over the image, and the cursor changes to . Click on the color you want to select.

 

To zoom into the image, press and hold the SHIFT key on the keyboard and click on the image. To zoom out of the image, press and hold the CTRL key on the keyboard and click on the image. Alternatively, use the mouse scroll wheel to zoom in and out. To move around on the image, click on the scroll bars to move up/down or right/left. Alternatively, press and hold the mouse scroll wheel down and drag the image on the screen.

 

Once the color is selected, it is entered into the Color column cell in the Vectorize Image dialog. If you make a mistake or click the wrong color, simply click again on the intended color on the image to update the color in the Color column cell.

 

To add a new color to the list, click Add below the color section. To delete a color from the list, click on the color in the dialog and click Delete below the color section. To delete all of the selected colors, click Remove All.

 

Color Tolerance

The Color Tolerance determines the range of colors identified by each color. The value is reported in the Tolerance column. Tolerance defines a similarity in color from one pixel in an image from another pixel in that same image. For instance, the blue rivers might be a darker value than the lighter colored lakes. If you only want the blue rivers vectorized, then you want the tolerance value low so the range of blue does not include the lighter blue lakes. Pixel values can range from 0 to 255. A low color tolerance is very similar to the pixel color selected. A high color tolerance fills the pixels within a broader range. Click and drag the to the right to broaden the pixel range of color. The tolerance number moves up as the slider moves right. This is useful for color images that have a variety of pixel color ranges near the edge or border. When the Color Tolerance value is zero, only the selected color is vectorized.

 

Edge Detection Method 

The Edge Detection Method determines how lines in the image are found. Available options are Edge Detection, Standard Object Thinning, and Enhanced Object Thinning. To change the option, click on the down arrow to the right of the existing option and select the desired option from the list.

 

If an image was previously processed using edge detection, erosion, dilation or one of the other processing filters, you should select Enhanced Object Thinning as the edge detection method from the list. If the image was not pre-processed, then either Edge Detection or Standard Object Thinning should be selected from the list for best results.

 

For most images that contain lines that should be vectorized, Standard Object Thinning is recommended because lines in images are generally a few pixels wide. The Edge Detection method would create a polyline on both sides of the line in the image. Standard Object Thinning creates one polyline through the middle of the line in the image.

 

 

The green lines are the vectors created using the Standard Object Thinning method.

 

The green lines are the vectors created using the Edge Detection method.

 

 

Canny Edge Options

Edge detection is useful for vectorization processing because it easily detects the edges of lines or color boundaries in an image and creates single pixel width polylines along the edges. The Canny Edge Options are only available when the Edge Detection Method is set to Edge Detection. If the options are not available, set the Edge Detection Method to Edge Detection. There are three options available in the Canny Edge Options section: Gaussian Standard Deviation, Hysteresis High Value, and Hysteresis Low Value.

 

Gaussian Standard Deviation

The Gaussian Standard Deviation is used to smooth the image and look for horizontal, vertical, and diagonal edges. To change the value, highlight the existing value and type a new value. Alternatively, click and drag the to the right or left. The value ranges between 0.1 and 3. Didger creates a convolution mask based on the value input. The 0.1 value creates shorter and more fragmented lines across the image. A 3.0 value creates longer, more continuous lines across the image.

 

Hysteresis High Value and Hysteresis Low Value

Hysteresis helps to connect lines based on angles and pixel value connectivity. To achieve this, hysteresis uses two different threshold values: Hysteresis High Value and Hysteresis Low Value. To change the value, highlight the existing value and type a new value. Alternatively, click and drag the to the right or left. The values range between 0 and 255. The Hysteresis High Value marks out the strongest edges of an image. Hysteresis traces these high value edges through the image. The Hysteresis Low Value traces faint sections of lines and avoids the few noisy pixels that do not constitute a line. Together these high and low values are able to identify edges and continuity in an image. Typically, the higher threshold can be set to approximately three times the lower threshold.

 

 

The green lines are the output from the Vectorize Image command using Edge Detection with an Hysteresis High Value = 30 and Hysteresis Low Value = 10.

 

The green lines are the output from the Vectorize Image command using Edge Detection with an Hysteresis High Value = 70 and Hysteresis Low Value = 210.

 

Post Processing Options

The Post Processing Options section contains options to control the final output of the vectorize command. This can generate smoother, longer lines or create polygons if a vectorized object appears closed.

 

Smooth Lines

The Smooth Lines option reduces the total number of vertices created along a polyline during the vectorization process. Available options are: No Smoothing, Minor, Moderate, and Aggressive. The default option is Minor, which applies a slight amount of smoothing to the vectorized lines. To change the amount of smoothing, click on the down arrow next to the existing option and select the desired option from the list.

 

For example, a polyline generated with No Smoothing creates many points and jagged edges. Setting the Smooth Lines to Minor removes some of the points and smooths the jagged edges to make smoother lines. Selecting Moderate for the Smooth Lines option reduces the number of points created during the trace without overly compromising the shape of the polyline. Selecting Aggressive for the Smooth Lines option reduces the number of points even further and simplifies the shape of the polyline. Some sections of the polyline may be removed with the Aggressive option.

 

Minimum Pixel Length

The Min Pixel Length option is the minimum number of pixels traced before a new polyline segment is created. To change the value, highlight the existing value and type a new value or use the to increase or decrease the value. Values range from 0 to 255.

 

The default is 10 pixels, which means that 10 pixels must be connected before a polyline object is created. Increasing this number results in fewer vectorized polylines with longer lengths. Decreasing this number results in more vectorized polylines, with potentially shorter lengths.

 

Auto Generate Polygons

The Auto Generate Polygons option is used to create polygons from the vectorized image when a polyline appears to close. Check the box to automatically create polygons. When the box is unchecked, polylines are created. The polylines can be converted to polygons by clicking the Draw | Change Boundary Type | Polyline to Polygon command after the vectorization is complete.

 

Retain Processed Image

The Retain Processed Image option is only available when the Colors to Vectorize is set to Complete Image. If the Retain Processed Image is not available, select Complete Image in the Colors to Vectorize section. When the box next to Retain Processed Image is checked, the altered processed image replaces the current image on the screen. When the box is unchecked, the original image remains on the screen.

 

Create Results on New Layers

The Create results on new layer(s) option adds the vectorized polylines and polygons to a new layer. This makes it easy to separate the image layer from the vectorized information. This option is checked by default. Uncheck the box next to Create results on new layer(s) to create the vectorized polylines and polygons on the same layer as the image.

 

OK or Cancel

Click OK to create polylines and polygons from the image. Click Cancel to close the dialog without creating any polylines or polygons from the image.

 

 

See also

Processing Filters

Image Registration and Warping

Processing Filters

Edge Detection