Nineteenth-century artists enthusiastically co-opted the `famous views' of Utagawa Hiroshige into the Western canon. But what exactly is a modern European to make of these misty picture-postcard views of Tokyo and the highways to Kyoto? Tom Lubbock surveys one show where landscape really is another country
Looks like rain? Not exactly. More an idea of rain. In Utagawa Hiroshige's Heavy Rain on a Pine Tree, a strip of dark black ink runs across the top of the picture, meaning raincloud - rather as, in a child's picture, a strip of blue across the top means sky. It makes a heavy weight above. It fades into a downpour, which falls against the white background in straight, vertical and barely broken lines - again, not what rain looks like, but how it often feels. The huge spreading pine on a promontory, which occupies the scene like a stegosaurus, is reduced to a silhouette of almost uniform grey, its colour and details quite lost in the precipitation. But this blurring doesn't touch at all the tree's closely observed outline, its shape kept clearly separate from the surroundings.

There's a set of exaggerations, then, simplifications, disparate observations pushed to their logical ends, conveying different sorts of information and sometimes, it seems, no information at all (why is the promontory's bank all bright blue?). A stylised or abstracted landscape, you might call it, but is that what it is? Certainly it was for that particular quality that Japanese prints were admired when they first got to Europe in the second half of the last century, after Japan's cultural isolationism was broken into by Commodore Perry.

Their devices - the flat colours, the delineated contours, the cut-off compositions - were enthusiastically picked up on and assimilated one way or another by almost every modernising artist. The Japanese print was co-opted as a sort of honorary branch of Western art, and Whistler put it up there with the Parthenon marbles as a milestone-cum-touchstone in "the story of the beautiful", a model of purity and delicacy.

The Royal Academy's Hiroshige exhibition, "Images of Mist, Rain, Moon and Snow", might give pause here. It's Hiroshige's landscape prints that make up most of the show, his "famous views" as they're so often titled - of street life in Edo (Tokyo), and of locations, land and sea, along the two highways between Edo and Kyoto, in all weathers. In Japan, Hiroshige's was a low art-form - popular, mass-produced images with a frankly touristic function - not the high, refined and aesthetic thing it was often taken for over here. Note too that the exhibition marks the bicentenary of the artist's birth.

An odd statistic, if you think about it. Two hundred years ago Japan and Europe had almost no shared history. The two cultures were on the same planet, but not in sync. Hiroshige's lifespan - he died in 1858 - was nearly simultaneous with (say) Delacroix's, but there's no relevant sense in which Hiroshige was the Frenchman'scontemporary. But then, he wasn't the contemporary either of the later artists, like Whistler and Van Gogh, who made their own use of him. His work isn't ours in the way such an anniversary implies.

We notice the differences, of course. But we can hardly help seeing them as interesting and delightful variations upon western art. Like children who think all foreigners really speak English, but mentally translate it into their own language, we can't but take this work as something that has been done to landscape art as we know it. Van Gogh praised its "extreme clarity". A hostile critic, and it's the same observation really, referred to the "dismantling of landscape". We today see and like these things too. But they weren't presumably points that its first audience would have noted.

We can at least try to make some relevant distinctions. The natural comparison is with Hiroshige's slightly older contemporary Hokusai, the other great exponent of the landscape print. And when it comes to clarity or dismantling, Hokusai is the master. His strength is for turning out very precise and inventive graphic equivalents for natural phenomena. Everything is highly characterised, for instance in his series of Waterfalls, where he coins for each torrent an individual identity, a shape and a rhythm, establishing its formula like a caricaturist.

On this score, Hiroshige is the weaker. His details, the shape he makes for a tree, a crag or a whirlpool, aren't so striking. The draughtsmanship isn't intense. His forms are not really to be enjoyed as details, more as a sense of detail. On the other hand, where everything in Hokusai, near and far, is clearly grasped by the mind and itemised, Hiroshige has a much stronger sense of visibility conditions. A mist in Hokusai is typically done as floating outlined fingers which overlap and obscure the scene. Hiroshige's mists are see-through: not shapes in their own right, but what mists leave behind, the world in fading silhouette. Things are still separate. A misty tree is a misty tree with firm contours. But the separate things coalesce into an atmospheric ensemble.

That's Hiroshige's forte: not the characterisation of things, but the creation of atmospheres. And if we notice still the isolated clarity of his separate effects, he's really working in the other direction, towards a unity of effect over the whole scene. That, of course, is Western landscape's point of pride, the way it can bring a scene together in the embrace of a unified light-source, and it's one of the big differences of Japanese art that it rarely uses this trick.

Hiroshige was certainly aware of it. Traffic had been going the other way for some time, and Western landscape painting had been known in Japan via Dutch traders since the start of the 18th century. Occasionally he used perspective, and cast shadows too, though as a kind of gimmick. Each figure in his People in a Moonlit Street has its little shadow on the ground, but the effect isn't followed up elsewhere in the scene. And it's not in this way that Hiroshige achieves his unifying moods.

It's remarkable how he does it. Different weather conditions - wet, wind, and fog - and times of day each come with their distinct and piquant illumination, and sometimes the sun or moon stands in the sky; and yet no general light falls in any particular direction. You can seldom say that some darker passage on the hills or water stands specifically for a shadow. What it seems to represent is shadowiness. And that's Hiroshige's trick. The lights and shades of a particular scene, though they aren't distributed as a Western landscape would do it, are all present, and present in exactly the right proportions.

Illumination is, so to speak, abstracted from nature, and reconstructed. It's all in the combination of separate tone and colour areas. You could take out the wooden bridge from People on a Bridge Surprised by Rain, give it another context, and it wouldn't be rainy at all. But where it is, its light pink boards introduce into the gloomy scene just the touch of brightness needed for the complex sense of daylight interrupted by sudden downpour. Likewise, those seemingly naive bands of deeper colour that run along the pictures' tops and bottoms: they're not at all realistic in themselves, but their contributory effect is enormous. Light doesn't go like that, but put the parts together and the mixture is true.

This wasn't something his Western admirers, taken with Japanese "dismantling" effects, could easily absorb, and nor could Hiroshige bring it off all the time. At least, his illuminations are sometimes so complex as to be unreadable as any weather in particular. Or is he sometimes after an illumination that is more than natural, something visionary? Or are we meant to feel and enjoy a play and strain between the image and the reality? The western eye keeps looking, but has to admit that, at many points, it really doesn't known

To 28 Sept. Royal Academy of Arts, London W1 (0171-439 7438)