Fig. 1. Image of the object surface with colored handwriting traces (in the rectangle on the lower right) and colorless handwriting indentations (in the rectangle on the upper left).

Fig. 2. Measured results of the depth of the trace: (a) the depth of local traces at I, (b) the depth of local traces at II.

Fig. 3. Image acquisition: (a) capture device, (b) the position of light sources; the blue circle represents the projection of the light source onto the horizontal plane.

Fig. 4. Colored handwriting traces applying RTI: (a) and (b) are in default mode, (c) and (d) are in specular enhancement mode.

Fig. 5. Colorless handwriting indentations applying RTI: (a) and (b) are in default mode, (c) and (d) are in specular enhancement mode.

Fig. 6. RTI of colored handwriting traces: (a) in default mode, NRSS=0.013743, (b) in default mode, NRSS=0.015857, (c) in specular enhancement mode, NRSS=0.042854, (d) in specular enhancement mode, NRSS=0.054382.

Fig. 7. RTI of colorless handwriting traces: (a) in default mode, NRSS=0.069636, (b) in specular enhancement mode, NRSS=0.082468, (c) in specular enhancement mode, NRSS=0.087245.

Fig. 8. RTI of colored handwriting traces: (a) in default mode, NRSS=0.294880, (b) in default mode, NRSS=0.297726, (c) in specular enhancement mode, NRSS=0.322620, (d) in specular enhancement mode, NRSS=0.337590.

Fig. 9. RTI of colorless handwriting traces: (a) in default mode, NRSS=0.416600, (b) in specular enhancement mode, NRSS=0.435858, (c) in specular enhancement mode, NRSS=0.455361.