Julian Opie Lisson Gallery, London NW1 to 17 March
Barbara Kruger South London Gallery, SE5 to 18 March
There's been no getting away from Julian Opie these past few months. Anyone who disagrees should look again - namely at all those billboards, buses, T-shirts and ads that promoted the latest album from Blur. There they were, over and again, four faces reduced to simple black outlines: Damon, Graham, Alex and Dave as they might have been drawn by Hergé. These images came in every size, from CD to full-scale hoarding. Nor was there any idea of a limited edition, based on some priceless original. If you bought the album, it could even be argued that you now own a quartet of Opie portraits.
I daresay most collectors would disagree, especially those prepared to pay £12,000 for a large Damon, or £18,000 for an outsize Alex. But that's the problem with a market that prizes the rare or unique - it can so easily be thwarted by an artist who doesn't hold back. Once Opie has fixed on his visual symbol, he will reproduce it in every conceivable format or size. A quick leaf through the catalogue he has produced for this show - based on those mail-order brochures for furniture or software - gives a comprehensive guide to the merchandise. You can buy animals, buildings and people as prints, wooden blocks or signposts. You can get landscapes on aluminium or video; portraits come in wallpaper or vinyl paint.
Opie's blithe attitude to what he sells is both humorous and winningly frank. After all, he could hardly pretend to be producing complex masterpieces, each carefully nuanced by hand. At 44, Opie has run through a lot of different ideas, from visual gags to neon sculptures and quietly minimal paintings. But he developed the notion of modular art - units that came in build-your-own systems - even before his Hayward show in 1994, and he's stuck with it ever since. Most of the work at the Lisson Gallery is update and diversification: landscapes, portraits and nudes, genres of old master painting.
The basic Opie unit is a representation of a representation. He takes a photograph, feeds it through a computer and then reduces it to a few quintessentials - for a portrait, it's the jawline, hairline, ears and neck, plus the features transcribed in his deadpan shorthand. This mainly consists of customised punctuation: angled commas, double hyphens and black full stops for eyes. Sometimes there are glasses; I specially like the way he indicates the rimless variety with a single ingenious contour. Occasionally there are highlights - rather sentimentally, in the eyes of children. The colour is bright and flat, the outlines have a zippy register and the final image is generally affectless, homogenised and irreducibly simple.
Some find these pictures playful; others feel that they are infused with melancholy. If that seems an extreme response, bear in mind that there are people who become distressed by that sign for Elderly People Crossing the Road. Opie understands the power of signs - he's exploited it with his strategic signposts of shy animals, described in reflective paint, ready to be caught in the headlights of a darkened road. But his portraits are more likely to erase than evoke emotion. They tell you how little can really be learned from a snapshot: the human animal caught in a flash.
Opie can take the riddles of representation too far, however, as with his stick-figure nudes. These are painted on building blocks - the head as a circle on a wooden cube, for example - and must have something to say about two versus three dimensions, though it's hard to tell quite what. But his ongoing series of roadscapes have got somewhere new by virtue of size. These generalised paintings, with their relentless white lines and views of mountains, trees and houses, used to be monotonously large. Now that they are tiny, like souvenirs, they instantly catch on your memory of other times and places.
To say that Opie repeats himself would be no more than a trade description. It's the slight variations that make all the difference to this road movie - the sense that there is always further to go and more to see on the trip. One Opie on its own can look blank or cute or even wilfully simplistic. Together, in his bulk-buy modular system, they add up to a bigger view of the world as a language of limitless images.
The South London Gallery has a video installation by Barbara Kruger , the veteran American moralist. You remember Kruger: 'I shop therefore I Am', 'Don't be a jerk!' and other accusatory or hortatory messages, generally printed on T-shirts or written up in neon, to the reported irritation of pedestrians in Times Square.
Kruger never whispers if she can possibly shout. This time, she has hired a bunch of screaming heads to do the job on her behalf. A dozen actors, on three video screens, yell repeated sequences of abuse in deafening unison: 'You're not cool/ skinny/ pretty enough!', 'I hate you!', 'Who do you think you are?' This cycle of rejection is occasionally broken by swift reconciliations, illustrating, I guess, the awful proximity of love and hate.
Kruger seems to be aiming for the brutal effects of Bruce Nauman, but the piece has none of his piercing directness - largely because her actors are so clearly reading from autocues. It's the same old problem with her work: exactly who is she addressing? After 40 minutes of this hammering cacophony, the main feeling you have, to borrow one phrase, is that 'it's got nothing to do with me'.
