Background and Objectives Early detection and elimination of dental calculus are imperative for prevention and management of periodontal disease. This study aimed to assess the efficacy of reverse contrast and sharpen image processing filters of indirect digital radiography for calculus detection. Materials and Methods: In this in vitro, experimental study, 95 extracted human premolars were mounted in a sheep mandible, and underwent digital radiography. Pieces of calculus measuring 0.5 mm in diameter were then adhered to the cementoenamel junction of the teeth and they underwent digital radiography again. Next, the radiographs were enhanced once with the sharpen, and once with the reverse contrast image processing filter. All radiographs were then observed by two observers. The sensitivity, specificity, and positive (PPV) and negative (NPV) predictive values were calculated. Results: The sensitivity, specificity, PPV and NPV of original radiographs, those enhanced with sharpen, and those enhanced with reverse contrast were 31%, 96%, 88% and 58%, 41%, 96%, 91%, and 62%, and 33%, 99%, 97% and 59%, respectively. The sharpen filter resulted in higher sensitivity than original images and those enhanced with reverse contrast. Reverse contrast resulted in higher specificity than the other two image types. However, none of these differences were statistically significant (P>0.05). Conclusion: Reverse contrast and sharpen image processing filters could not significantly enhance the detection of calculus on digital radiographs.