4.1.1. Red Color Filtering

As shown in Figure 1, the numerals are written in red color in the majority of these registers. However, not only the numerals but also the updates are written in red and we have to distinguish them from the numerals. In order to spot them easily, we applied a red color filter on the documents. We converted the image from RGB representation to HSV. The upper and lower limits for the red color used in these historical documents are determined by trial and error. Lower HSV thresholds were selected as (170;70;50), whereas the upper HSV thresholds were determined as (180,255,255). An example original image of the register and the filtered one is shown in Figure 3. The mask background color was chosen as black.

**Figure 3.** In the left, the original register image is shown. In the right, the resulting image after applying a red color mask is shown.
