Fig. 8.

Change in normalized thermal strain maps produced by different-sized Sobel operators in an in vitro study with a peak temperature increase of 4.3°C. Operator dimensions from 0.06 × 0.06 mm to 3.30 × 3.30 mm were evaluated. The effect of increasing dimension was small for operators larger than 2.3 mm (a). Examples of subtracted images are shown, between 0.06 and 0.98 mm (b), between 0.98 and 1.95 mm (c), and between 1.95 and 2.91 mm (d).