The Weekend's Television: Skellig, Sun, Sky1Red Dwarf: Back To Earth, Fri, Dave

"You've got to picture it in your mind's eye, son," said Michael's Dad as he showed him round their new house, a wreck of a place whose ambience is not improved by the Stannah stairlift in the hallway and the flush toilet plumbed into the corner of the living room. The invitation to see what isn't there is good advice for first-time home-owners seeking a bargain, and, as it happens, for readers of books. But it also reminded you of the peculiar difficulty of filming a novel like Skellig, David Almond's award-winning story about a young boy who finds someone very odd living in his garden shed. All of a sudden you don't have to picture it in your mind's eye at all, and that means that details that were helpfully opaque and unspecific on the page get focused very precisely on the screen. Particularly precisely here, where Sky's desire to have a big high-definition drama to boost sales of its HD service means there's a premium on fine-grained close-up.

As if to show-off the technology, Annabel Jankel's film began with a mesmerising swirl of starlings across a twilight sky, every bird pixel-sharp, and our early glimpses of Skellig (played by Tim Roth) himself, presented him in unequivocal clarity. A nictitating membrane shuttered eerily across his eyes and his skin had the pouchy texture of a bird's wattle. (The woodpecker, incidentally, closes its nictitating membrane a millisecond before it strikes the treetrunk, in order to prevent its eyeballs from flying out of its head, a fact that has no bearing at all on Skellig's merits as television drama, but seemed too good not to pass on).

David Almond is deliberately reserved about the exact nature of the bird-man hybrid at the centre of the story. Is he a derelict angel, reduced to scavenging Chinese takeaway leftovers from the bins? Or is he some kind of revolutionary throwback, a living fossil who still has the wings that in us have shrivelled down to our shoulder-blades, as Michael theorises at one point? There are hints and nudges in both directions but no conclusive proof, and no firm indications as to whether Michael has summoned his experience out of his need to escape his mundane anxieties, about being shoved from his privileged place in the nest by a new baby sister. The film version – with the form's inherent weakness for the spectacular – couldn't afford to be quite so unspecific and had taken a few liberties with the original. Nobody, I take it, will have problems with the textually sanctioned moment when Michael, Skellig and his friend Mina lifted into the air in a moment of mystical togetherness, though it seems odd that Skellig had to instruct them to "remember this night". How the hell would you forget exactly? And purists might share my uncertainty about the moment that Skellig took to the sky with Michael in a swooping joy-ride reminiscent of the animated version of The Snowman.

Skellig was filmed in the washed-out, bluey tones that are familiar from upmarket police thrillers, and Jankel's finest touches came not with the CGI add-ons, which only stirred unhelpful thoughts about the airworthiness of Skellig's threadbare, battery-hen wings, but with little touches that recovered the did-I-see-it-or-didn't-I quality of Mikey's first encounters with his grounded angel. At one point, he had a flashback memory of the old lady he befriends at the hospital, when his baby sister is on life support. She's walking away down a long corridor and her dressing gown parts at the back to show a flare of white nighty, like a ladybird cracking open its shell to unfold its wings. Not in the book, if my memory serves me right, but a far truer nod to the magical ambiguity of Almond's book than the full-on aerial joyride.

Science-fiction fans won't have known quite where to look over the weekend. Dr Who was back, trailing a couple more guest celebrities in its comet tail. The Sci-Fi channel was running a tribute to Gerry Anderson's Supermarionation techniques and – the one that's had the fan-site servers running overtime – Red Dwarf: Back to Earth returned for a three-part special. Watching the first episode I thought there was something a little strange and airless about it, an odd hesitancy in the performances that suggested the comic muscles had stiffened during nine years of suspended animation. Then I realised that the laugh track was missing. I don't know whether one was added before transmission, but it had an odd effect on my viewing at first, as if the performers were leaving room for a reaction that was to be pasted in later. I did add some of my own sound effects though, first of all when Rimmer sentimentally sat down by Kochanski's headstone to read aloud to her departed spirit. "I pray God there's some car chases in this one," he said, splitting open a copy of Sense and Sensibility. And I was provoked to a question. How come Chris Barrie just crawls around on big machines these days, when he's such a good comic actor?