Figure 2

Image processing of S-shaped canal. (Stage 1A) the photograph was desaturated before instrumentation; (Stage 1B) the photograph was desaturated after instrumentation; (Stage 2A) the image was converted into vector one before instrumentation; (Stage 2B) the image was converted into vector one after instrumentation; (Stage 3) images pre- and postinstrumentation were superimposed into one after acquiring their central axis; (Stage 4) measuring the distance of central axis pre- and postinstrumentation. The green line, red line and white line represented the central axis of original root canal, the central axis of enlarged root canal, and the outline of root canal respectively.