KATE BETTS, The New York Times, reports:

MADONNA and J.Lo depend on him. Annie Leibovitz and Steven Meisel won’t print a picture without him. Anna Wintour and Graydon Carter shell out many thousands of dollars a year for his services. He’s arguably one of the most powerful men in fashion, but he doesn’t sit in the front row or wear designer clothes, and you certainly won’t find him on the Style network coughing up deep thoughts about Gwen Stefani’s Super Bowl outfit.

Come to think of it, though, there is probably no one who has such a close knowledge of Gwen Stefani, down to the pores of her powdered cheek.

This behind-the-scenes magician, more intimate with celebrity flesh than a personal trainer or a masseur, is Pascal Dangin, the digital retoucher for fashion’s and Hollywood’s most famous photographers. Some refuse to work with anyone else. On the glossy side of the newsstand just this month, he tweaked the covers of W, Harper’s Bazaar and Allure.

In a field where designers, photographers and stylists want to be celebrated for their every flourish of innovation no matter how dubious — topless models with vacuum cleaners, anyone? — the French- born Mr. Dangin, the founder and chief executive of the foremost photo retouching business in the country, Box Studios in New York, cultivates his anonymity.

“I never want to talk about my work, because it’s kind of taboo,” he said. “The people who benefit from my work do not benefit from me talking about it.”

While photo manipulation is more prevalent than ever in this digital age, when many laptops come with software to help get the red out of your mother-in-law’s eyes, the extent of retouching practiced by glossy magazines is still little understood by readers. At the same time, insiders offer a shrug of indifference: of course the camera can be made to lie. Do you really think that’s Kate Winslet’s figure on the cover of British GQ this month?

“Hey, everybody wants to look good,” said Mr. Dangin (pronounced dawnh-GANH). “Basically we’re selling a product — we’re selling an image. To those who say too much retouching, I say you are bogus. This is the world that we’re living in. Everything is glorified. I say live in your time.”

Although most newspapers, including The New York Times, forbid the distortion of news photographs in a lab or on a computer, at fashion magazines it has long been standard to throw in a little digital pixie dust to make a model’s eyes bluer, her teeth whiter, her legs slimmer. Periodically, such highly tweaked images stir controversy, proving that the retoucher’s skill is still viewed as something of a dark art. Ms. Winslet, who is well known for waxing content about her healthy womanly figure, was at the center of the latest flare-up when she complained of being overly slenderized for the GQ cover. “The retouching is excessive,” she was quoted as saying in The Daily Mail. “I do not look like that, and more importantly, I don’t desire to look like that.”

Dylan Jones, the editor in chief of British GQ, defended the retouching. “I really don’t see anything sinister in this,” he said by e-mail. “It’s been going on for years. Essentially we all want glamour. We all want show business.” A second controversy arose around the body-positive Ms. Winslet when Women’s Wear Daily reported two weeks ago that her head had been digitally placed on the torso of a slimmer stylist on the cover of the January issue of Harper’s Bazaar. The report was denied by the magazine and by a spokesman for Ms. Winslet.

That episode suggests that there are some lines that the image manipulators at glossy magazines will not cross. Mr. Dangin has on occasion pieced together a cover photo by putting the model’s head on a different picture of her own body, but he rejects the Dr. Frankenstein brand of photo splicing.

“I would not put an actress’s head on a stylist’s body — no!” he said. He said it would be too hard to make such a composite convincing, and acknowledged that it would also raise an ethical question. “People can get very upset,” he said. “They put it in the same pool as human cloning.”

Retouching was once an obscure and narrow practice by photographers who would cover skin and body imperfections in their prints using tiny brushes. Now it entails whole new realms, drawing on the power of computer technologies to improve light, color and contrast in photos, not to mention thighs and heads. Mr. Dangin retouches and prints the work of a dozen leading fashion photographers, including Michael Thompson, Mr. Meisel, Craig McDean, Steven Klein, Inez van Lamsweerde, Mario Sorrenti and David Sims. He also works with a handful of art photographers like Philip-Lorca diCorcia. Some photographers refuse to work with anyone else.

“He is much more than just a technician who removes pimples,” said Mr. McDean, who had Mr. Dangin flatten the background and simplify the colors in a Madonna portrait to create a 50’s look for the cover of Vanity Fair last year. “He’s a thinker, too. He’s not someone who just pushes a button. There’s some kind of soul in it, which is very rare. He can physically express himself through the computer.”

The color, flesh tones and bodies aren’t the only things tweaked in photos. Sometimes the composition isn’t real, either. One example is in last fall’s ad campaign for “The Sopranos.” Although it seems that the photographer, Ms. Leibovitz, shot the entire cast around a table, she actually took them separately, and Mr. Dangin assembled the images in his computers.

Photographers and art directors swear by Mr. Dangin’s ability to marry a deep knowledge of photography with technology. “Before I met Pascal, I couldn’t do so many different kinds of lighting,” said Patrick Demarchelier, a prolific shooter of Harper’s Bazaar covers and fashion advertising. Because of Mr. Dangin’s ability to correct the harsher aspects of dramatic lighting, he said, he has been able to go beyond conventional studio lights. “He has introduced a new brand of photography that didn’t exist before,” he said. “Without Pascal, a lot of photographers would not exist today.”

For all his technological expertise, it is Mr. Dangin’s rapport with photographers and his slow, meticulous pace that seem at the center of his success. “Some photographers won’t work unless he does the retouching and printing,” said Raul Martinez, a partner in the advertising firm of A/R Media in New York, who often works with Mr. Meisel. “He has real personal relationships with them, and they trust him.”

For somebody who devotes his time to glossing up the images of others — at fees of $500 for an inside magazine page up to $20,000 for a cover image requiring lots of digital cutting and pasting — Mr. Dangin is decidedly unpolished. His tobacco-stained teeth have not been whitened, and despite his stature and success, he wears grungy brown corduroys, a Champion sweatshirt and New Balance sneakers every day. An unruly mass of finger-in-the-socket curls belie his background as a hairdresser.

Watching Mr. Dangin at work at his Box Studios on Broadway near Spring Street, which employs 40 people, is like ducking behind the curtain to see the last stage in the manufacture of film and fashion celebrities. In a pitch-dark loftlike room packed with high- definition computer monitors and light boxes, more than a dozen retouchers hunch over keyboards clicking and pointing and drawing. A huge Oz-like computer server buzzes in the background. The wizard himself sits at a giant triptych of screens. If the one in the middle is the canvas, then the two side screens are like palettes holding the software icons and files of images.

At any given moment, Mr. Dangin juggles about 10,000 files. Not long ago he was tending to an ad campaign for Cover Girl cosmetics that uses Angela Lindvall, a model; a Leibovitz image to promote the next “Sopranos” season; and a Steven Klein portrait of Madonna for a magazine cover.

“This part is too light, so I am going to basically start to burn it in and bring in more density,” Mr. Dangin said, scribbling with a stylus on a computerized drawing pad as he adjusted the color and contrast in a photo by Adam Bartos, an art photographer. “It’s about changing light. Think of this as a virtual darkroom, where you would expose parts of the photo to make it denser. Only in a darkroom, that would take five hours, and here we do it in an instant.”

In a culture in which image is a major commodity, the paradox of appearing natural on film is nothing new. As far back as the mid-19th century, the photographer Mathew Brady employed retouchers to improve formal portraits. In the early 20th century, Man Ray used innovative techniques like solarization, and in the 1930’s and 40’s the Hollywood photographer George Hurrell elevated actresses like Jane Russell and Joan Crawford into icons of glamour by lengthening their eyelashes, smoothing every wrinkle and blemish and highlighting their hair.

Taking a cue from Hurrell, Richard Avedon retouched many society portraits by hand, famously extending the neck of Marella Agnelli in one to make her look literally like a society swan. More recently, artists like Cindy Sherman have used retouching and manipulation to transform identity completely — a process that is now common, but has not always been embraced. In 1997, the fashion photographer David LaChapelle squabbled publicly with one of his subjects, the actress Mira Sorvino, when he transformed her image digitally into a facsimile of Joan Crawford for Allure.

These days, anybody can retouch a photo. Web sites like Photo-Brush and the Pixel Foundry sell software that teaches photo-manipulation techniques, which are also described in books like Scott Kelby’s “PhotoShop 7: Down and Dirty Tricks.” As a result, almost any photo and image, both personal and public, can be retouched: high school yearbook pictures, family Christmas cards and online dating head shots.

Which raises the perennial question about Mr. Dangin’s work: how much is too much? Is straightening your child’s teeth on a Christmas card in the same category as straightening the teeth of a celebrity mother of septuplets, for which Newsweek was criticized in the late 1990’s.

The only certain answer is that the line between what is in bounds and what is out is a moving one in the digital age. Grabbing a printout from a recent Yves Saint Laurent ad campaign, Mr. Dangin shrugged. “This world is not reality,” he said, fingering the print. “It’s just paper.”