The secrecy also made it difficult for printer makers to make Postscript-compatible printers.

Hewlett-Packard and Xerox are among the printer makers that sell their own paper as well.

But the big printer makers still hold more than 95 percent of the ink cartridge market.

Mr. Yarkin also sees growth through potential alliances with printer makers.

The printer makers argue that the modifications are product improvements.

The biggest problem the printer makers had to solve, then, was this: How do you indicate which photos you want to print?

Some printer makers combine all the colors into one cartridge, which is convenient during installation.

Some also face legal challenges from big printer makers.

H.P., as the big computer and printer maker is known, was suffering badly in the industry slump.

The refillers have put a dent in the printer makers' business.