The performance of locally set thresholds.

The percentage of the pixels a test image that were correctly designated was measured. The test image (to Figure 1:2) was an extended version of Figure 1A2 with a wider range of diameters (1–55 pixels). Six areas were examined: the objects (foreground), the annulus inside the objects (Figure 2), their centres (objects excluding the annulus), total background, the annulus outside the objects (Figure 2) and the remaining background (excluding the outer annulus). The annulus included all pixels, outside or inside, within 10.5 pixels of the objects‘ edge. Data shown are means, N = 8.The performance of locally set thresholds.