CHATSWORTH, Calif., April 1 -- International Remote Imaging Systems Inc. reported that net revenues for 1998 were $27.5 million, essentially the same amount as in 1997. Operating income improved to $556,000 compared with $246,000 for the prior year. The company incurred a loss of $385,000 (or $0.06 per diluted share), compared with a loss of $503,000 (or $0.16 per diluted share) in the prior year. Earnings before interest, taxes, depreciation and amortization (EBITDA), an indicator used in estimating cash generated by the company, were $3.4 million compared with $4.0 million in 1997.In the fourth quarter ending Dec. 31, 1998, net revenues were $7.1 million, compared with $7.4 million in 1997, while EBITDA was $680,000, compared with $892,000 the prior year. The net loss was $272,000 (or $0.04 per diluted share), compared with a net loss of $533,000 (or $0.09 per diluted share) in the prior year. EBITDA was more than sufficient to cover scheduled principal and interest payments on debt obligations. IRIS reduced its debt by $1.0 million during 1998.