David Hockney: Drawing in a Printing Machine, Annely Juda, London

Twenty years ago, a friend in Notting Hill had a call from David Hockney, a friend of his.

Hadn't he liked the artwork Hockney had sent him, demanded a querulous voice from Los Angeles. Our mutual friend was puzzled: nothing had been delivered.

Hockney, chuckling, explained that it wouldn't be arriving by post – that his latest, multi-part works were made to be faxed. But it turned out the artist had mis-dialled. Somewhere in London, someone had watched, mystified, as page after doodled page had churned from his fax machine, no doubt to be scrunched into balls and tossed, in annoyance, into a bin. How much is an original Hockney worth? It could keep a person from sleeping.

David Hockney has always been a playful artist and a geek, and both qualities are present in this story. The question of how much a Hockney is worth is hugely open to debate if that Hockney has been faxed. At the same time, there's no doubting the excitement this artist gets from technology. And the same applies now that the artist has discovered Photoshop.

The works in his new show, Drawing in a Printing Machine, are described as "inkjet-printed computer drawings". Using a graphic tablet and a tablet pen, Hockney has produced a series of images, some drawn, some a mix of drawing and photography, and one – a wall-length panorama called The Twenty -Five Big Trees between Bridlington School and Morrison's Supermarket on Bessingby Road, In the Semi-Egyptian Style – a photomontage. The foreground grass of this last work has some of Hockney's characteristic squiggles on it, but how small can an artist's input be before a work ceases to be by him? To what extent is a Hockney drawn on screen and run off a printer, a Hockney?

The answer to this last is: whatever the market decrees. The art of the past 80 years has been riven with work that questions the value of authorship – Duchamp's readymades, Warhol's screenprints – but Hockney differs in his old-fashioned attachment to drawing. These are not photographic reproductions but prints, he insists; not a rejection of tradition, but a refinement.

And what are they like, these works? Well, the portraits look like the crayon and gouache Hockneys of a couple of years ago. There are passages where you feel the artist's excitement at his recent plaything – the gestural pink table in his picture of Peter Goulds, say, but otherwise it's business as usual. The landscapes are more experimental and so more arresting, if patchier. Autumn Trees Near Thixendale is lovely, Hockney finding in the approximations of Photoshop's palette an accidental counterpoint to his own.

In the end, though, the works are rather like Hockney himself, the Bradford boy in Hollywood. One of the things he loves about Photoshop, he says, is that it is the art machine of the masses, that anyone can do it. Some of the new works look as though anyone has. Their price tags, however, do not.

To 11 Jul (020-7629 7578)