DEVORAH SPERBER, "Post-Digital: 800 Lbs. of Pixels," HEREArt, 145 Avenue of the Americas, at Spring Street, (212) 647-0202 (through April 7). Ms. Sperber strings thousands of spools of colored thread into curtains, which when viewed in strategically placed convex mirrors resolve into remarkable painterly illusions of a sunny, rocky coastal scene or an expansive stone wall. A floor piece made of 18,000 colored-coded pen caps is magically transformed by a mirror into a fine, tranditionally patterned Oriental rug. What will this inventive artist do next? -Ken Johnson, March 23, 2001