# Blue Read Tool Sampling Tool Parameters

The Sampling tool parameters control the way that images are sampled during training. For more information, refer to the Sampling Method topic.

Note: Changes to the Sampling parameters after a tool has been trained will invalidate the training, because the underlying image statistics may be fundamentally changed, which will necessitate retraining the tool.

Parameter | Description
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Feature Size | Specifies the typical feature diameter, in pixels. The Feature Size parameter is graphically displayed in the lower left of the image, and can be graphically resized within the image to set a more accurate size. Feature size strongly influences processing time (n2), in other words,, a Feature Size of 100 is 100 times faster than a size of 10, while a Feature Size less than 15 usually does not yield good results. When setting the Feature Size, consider the following in regards to Processing time (Ptime): Note: The tool will actually see an area five times larger than the Feature Size setting. However, the level of detail will be much higher in the center of the feature, as opposed to the periphery. For more information, refer to the Feature Size topic. For the Blue Read Tool, the Feature Size is two-dimensional, Width x Height.
Polarity | The Blue Read tool was pre-trained on a set of images with a consistent text and background polarity, in other words, dark text on a light background, if you happen to have a data set of images with an inverse polarity, you will need to change the polarity by selecting Inverted from the Polarity drop-down menu. When this parameter is set to Inverted, the images in the Images display, as well as in the main display, will show the corrected polarity. Note: This change in polarity only applies to the Blue Read tool, and any subsequent tools chained to it will keep the original image greyscale polarity.
Border Type | Specifies how pixels on the outside of the image are sampled. For more information about how this parameter affects sampling, refer to the Sampling Method topic. Tip: Adding an additional mask at the boundaries of the image highly reduces the false detection rate. Black: Fills the outside of the image with a solid color, black. Replicate: Fills the outside of the image with the last pixel.
Masking Mode | Specifies how a mask will be applied to the sampled image. A mask is used to limit areas of the image processed by the tool. Note: Masks can be set after training, however, setting them prior to training will help the learning phase. Transparent: Samples are only collected within the unmasked parts of the image, but data from the Context Region is also collected from the areas that are masked. This ensures that features or defects that are at the boundary of the mask or ROI generate the same response as features or defects that are centrally located. Mask: The mask is used to ignore the areas which are masked. All pixels that are masked are set to 0, which prevents data from the masked parts of the image from being considered during training or runtime. However, it also alters the response of the tool to defects or features near the mask boundary. This setting also works to focus the tool toward the center of the ROI. Overlay: The mask is added to the sampled image as an additional color channel.