The painter David Hockney has been a consistently exciting photographer for many years. Not only that. He has been a consistently fascinating theoretician of photography, too. In a lecture he gave at the UK’s National Museum of Photography in Bradford in the mid-1980s, he explained something of the rationale of his “joiners” (collaged multiple photographs in which the perspective perpetually renews itself, challenging the monocular single frame to which we’re accustomed) in terms of keeping the viewer’s eye on a picture longer. The eye, I recall him saying, skids off the shiny surface of a photograph as it does not off a drawing or a painting, and needs help to slow it down. This is an essential idea. The photographic surface is problematic; the joiners were one compelling answer.

Another strand of Hockney’s thought has been that photography has a more important place in the history of art than it is usually given. His 2001 book Secret Knowledge hammers home the thought that the camera existed and was in regular use long before any means of chemically fixing its image.

Hockney has embraced new technologies for their picture-making possibilities. He had a Xerox period (he insisted that the Xerox was a printing machine in its own right, not merely a copier). He has used faxes and iPhones. The lowly SX-70 Polaroid was a favoured tool for many years.

Hockney’s latest excursion is to the very edges of photographic territory. He has found that Photoshop and other imaging software packages are now good enough for him to draw directly within them. At the Annely Juda gallery in London, he shows images drawn using a computer-generated palette, and switching between finishes that look like watercolour, oils, lino-cut or, when he likes, photographs. The show is divided into two parts: portraits, which are at a further remove from photographs; and landscapes, which are closer.

In an image such as “Summer Road, Near Kilham, 2008”, we see Hockney’s virtuoso orchestration of his different elements. There is a high plunging view of farmland in which the upper corners are framed by branches in the manner of many rural scenes made at a lesser elevation. Are we in a tree-house?

The (computer-)drawn elements are sometimes in the manner of washes, translucent overlays of colour, sometimes more opaque in order to hide distracting detail. The colours have Hockney’s trademark brightness, and include a purple road disappearing into the depth of the picture. The view includes passages of lyrical colour in the rendition of foliage, lots of different greens competing for density and depth.

The photographic elements of the piece have seams, exactly like the joiners all those years ago, visible edges where one photograph butts up against another. These remind one that the artifice in photography is just as unnatural as that in draughtsmanship or in paint. A farm in the distance is very photographically legible, more so than many closer elements, which we have to reinvent for ourselves from quick scratchy Hockney marks. The overall effect is entrancing, a real landscape that the painter could have dreamed up. The balance of quotation and fresh thinking is magically right.

Another picture rejoices in the title “Twenty-Five Big Trees Between Bridlington School and Morrison’s Supermarket on Bessingby Road, in the Semi-Egyptian Style, Monday 23 February/Thursday 26 February/ Friday 27 February 2009”. It can comfortably carry this unwieldy handle – it’s a vast linear frieze, eight metres long by a metre tall.

The trees of the title border playing fields. They are seen over the road that lies close to the lower edge of the picture. In the context of this exhibition, in which many of the other views are of the ordered landscape of English parkland, the steel safety barriers act as parodies of the beautifully understated estate fencing still visible all over the English landscape. The trees, too, look more exotic than the standard English roadside menu, and I wonder if Hockney hasn’t used his Photoshop to import a favourite or two from California.

The sky was dull on the days Hockney photographed: he has added “painted” marks that look like the effects of polarising sunglasses: a little more definition in the clouds, a little more contrast between cloud and void. It demands to be read in detail. At one end, a sign denies access to the fields, a Calvinist view of Elysium in Bridlington. Hockney has added a row of 10 or so tiny but classic English decorated church towers in the woody fringe between sky and land. I think (without being sure) that one of the sports pavilions half-visible through the screen of a hedge has cloned itself further along the frieze. Closest to us, where they are most obviously not to be misread, the painterly marks are more visible.

Photography years ago eliminated the need for arduous draughtsmanship. Yet here is Hockney elaborately painting by hand the grasses in the foreground, precisely where a photograph could have saved him all the effort. It’s a wonderful picture, a deliberate tango between fact and fiction, playing on our expectations of each with masterly control and leaving us with something beautifully composed between the two.