## Simpler Calculation

- Compute difference of two color channels after scaling “brightness” and “contrast”
- Make “parchment” and “overwriting” subtract to same gray value

## More Sophisticated Calculation

- Find combinations of the three colors (R,G,B) that estimate the three classes
- “Parchment”
- “Overwriting”
- “Underwriting”

- Find combinations of the three colors (R,G,B) that estimate the three classes

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