Use the settings on the Threshold tab to determine how you want OCR to calculate the threshold value it uses to segment objects on an image.
Complete the following steps to set up thresholding:
- Select the Threshold tab, and select a threshold Mode:
- Fixed Range—A method in which you manually determine the threshold value for the entire ROI.
- Uniform—A method in which OCR calculates a single threshold value for the entire ROI.
- Linear—A method in which OCR divides an ROI into the number of blocks you specify, calculates a threshold value for the first and last boxes, then linearly interpolates values for the blocks in between.
- Non Linear—A method in which OCR divides the ROI into the number of blocks you specify, and calculates a threshold value for each block. Specify the number of blocks on the Advanced Threshold tab.
- If you selected Fixed Range in Mode, use Min and Max, or the slider at the bottom of the histogram, to set the threshold value.
- If you selected Uniform, Linear, or Non Linear in Mode, select Dark on Light in Characters if the image contains dark characters on a light background. Select Light on Dark in Characters if the image contains light characters on a dark background.
- Enable the Reject Particles Touching ROI checkbox to ignore particles that are touching the border of the ROI you drew.
- In Remove Particles (Erosions), select the number of erosions you want OCR to perform to remove small particles from the ROI.
As you manipulate settings on the Threshold tab, OCR displays segmented objects in blue.
Tip If the objects in the ROI are not segmented as you expect them to be, experiment with settings on the Threshold, Advanced Threshold, and Size & Spacing tabs to improve the segmentation.