# Blue Read Tool Processing Parameters

The Processing parameters control the way that images are processed by the tool. Changing these parameters does not require the tool to be retrained; the effect can be seen right away by reprocessing the database.

Note: The Feature Filter parameter is only available when Expert Mode is enabled.

Parameter | Description
--- | ---
Sampling Density | Specifies the density of sampling points with respect to the tool's Feature Size (FS) setting. The sampling density determines the degree of overlap between adjacent samples. A sampling rate of 1 means that the sampling location is incremented by the feature size between samples. The default sampling rate for most tools is 3, which means that the sampling location is incremented by one third of the feature size. Tip: One key aspect of the Sampling Density parameter is the relationship between the tool's processing time and accuracy. A tool's processing time depends approximately quadratically to the Sampling Density (Sd) value. For example, a Sampling Density setting of 1 is approximately nine times faster than a setting of 3 (n2). While higher Sampling Density settings are more accurate, it significantly impacts the processing time of the tool.
Threshold | The Threshold determines how closely the found character must be to the desired character for it to be considered. The found character must exceed the setting.
Angle Range | Provides for degrees of freedom (DOF) of features than can be reported by the tool. Specifies the specific range of rotation that can be accommodated by the tool. Note: For more information, refer to the Blue Locate Tool Features Parameters topic.
Size Range | Provides for degrees of freedom (DOF) of features than can be reported by the tool. Specifies the specific range of scale that can be accommodated by the tool. Note: For more information, refer to the Blue Locate Tool Features Parameters topic.
Feature Filter | Specifies a filter based on feature id, x, y, size and orientation, which is used as criteria for found features. By specifying a filter for features, features that do not match the filter will be removed from the results. If the parameter is left blank, all features will be returned. Since this filtering is done after the tool has processed the images, the features are not removed, simply hidden from the results. Features that are not present due to the filter will reappear, without reprocessing the image, by removing the filter criteria. Note: The syntax for filters is the same as that used for Display Filters. For more information about constructing the syntax for a filter, see the Custom Display Filters. For example, if the Feature Filter parameter was set to the following:
Feature Filter | Description
--- | ---
x in [0,view.width] and y in [0,view.height] | With this filter, only features whose center is within the ROI will be returned.
(id = '0' and x < 200) or (x='1' and x > 200) | With this filter, assuming a View that has a width of 400, features that have an ID of 0 and are on the left, and features that have an ID of 1 and are on the right, will be returned.