White Gap element in FlexiLayout Studio finds empty rectangular areas using object histograms, with orientation, size, and threshold properties.
White Gap is an element of a FlexiLayout that describes a rectangular area on the image that contains almost no objects of the specified type.To look for White Gaps, the program creates histograms for objects. When creating histograms for the objects in the search area, the program calculates the sum of the projections of all the objects on the horizontal axis (to look for a vertical gap) or on the vertical axis (to look for a horizontal gap).If the sum of the projections is smaller than the specified threshold, the program considers the area to be a White Gap.
Building a histogram for a vertical gap
For more information about histograms, see Hypotheses for White Gap elements.The search area can contain stray objects. The maximum allowed number of such objects is specified in the properties of the element.White Gap elements are marked with in the FlexiLayout tree.
To open the Properties dialog box, right-click the element in the FlexiLayout tree and select Properties… on the shortcut menu.To describe the corresponding object, click the White Gap tab.
Property
Description
Orientation
Sets the orientation of a White Gap. The two orientation values are described in the following table.
Min width/height
Sets the minimum width/height of a White Gap in the direction perpendicular to Orientation. Gaps of smaller width/height are ignored. Measured in the user-defined units of measurement. The default value is 20 dots.
Search among objects of type
Sets the type of objects among which to look for the White Gap. Select the objects by checking the boxes next to them.
The Orientation property has two values:
Orientation
Description
Vertical
The top and bottom boundaries coincide with the top and bottom boundaries of the search area. The left and right boundaries must be detected. An example of a vertical White Gap is the space between two text columns.
Horizontal
The left and right boundaries coincide with the left and right boundaries of the search area. The top and bottom boundaries must be detected. An example of a horizontal White Gap is the space between two paragraphs of text.
Histogram properties for objects in the search area
Property
Description
Lower threshold limit
Sets the minimum level of the histogram. This property allows other objects in the search area. If the height of the histogram of the objects is greater than the number specified in this field, the program considers the search area to contain no gaps. Measured in the user-defined units of measurement. The default value is 37 dots.
Upper threshold limit
Sets the maximum level of the histogram. This property excludes false histogram maximums that can be caused by large numbers of vertically arranged stray objects in the search area when looking for a vertical gap, or horizontally arranged objects when looking for a horizontal gap. Measured in the user-defined units of measurement. The default value is 150 dots.
Threshold coefficient (%)
Sets the maximum relative level of the histogram. The relative level of the histogram is calculated as [level of histogram] / [histogram maximum in search area]. The default value is 20.
The values of Lower threshold limit, Upper threshold limit, and Threshold coefficient (%) can only be selected by trial and error. Start with the default values. If the results are unsatisfactory, try to find values that enable the program to detect the White Gap on all of the test images.
If the value of the Threshold coefficient (%) is smaller than the value of the Lower threshold limit, the Lower threshold limit is used. If the Threshold coefficient (%) is greater than the Upper threshold limit, the Upper threshold limit is used (that is, the program uses the strictest criterion).
in the FlexiLayout tree.
