Figure 3.

An example of trimming. The consecutive squares represent the bases of a read with 45 bp, where the black color squares denote the bases with low quality scores, and in contrast the white color squares are the bases with high quality scores. There are eight bases with low quality scores in the read. When K = 4, the read is trimmed into a longest segment which contains four low quality bases, and when K = 3, the read is trimmed into a longest segment which contains three low quality bases.