Fig. 3.

Relationship between mean optimum brightness-area-product threshold ($\stackrel{‒}{{\mathrm{BAP}}_{thr}}$) and mean background intensity after adaptive histogram equalization ($\stackrel{‒}{I_{b-ahe}}$). Each marker represents the mean across all frames in a scan. The solid line represents the relationship that was used to determine the $\stackrel{‒}{{\mathrm{BAP}}_{thr}}$ for a particular scan when $\stackrel{‒}{I_{b-ahe}}$ was calculated from the images. When $\stackrel{‒}{I_{b-ahe}}$ was less than 128, $\stackrel{‒}{{\mathrm{BAP}}_{thr}}$ was constant (2411), and otherwise it was equal to $\stackrel{‒}{I_{b-ahe}}$ x m₁ + b₁ (Eq. 4), where m₁ and b₁ are given in Table 3. The coefficients m₁, b₁, and the transition intensity changed after March 1, 1999 (data shown were from scans after this date).