By SARAH KERSHA

For centuries, philosophers and scientists have tried to define a universal ideal of beauty. Now a computerized ¡°beautification engine¡± uses a mathematical formula to alter a person¡¯s photograph into a theoretically more attractive version, while maintaining what the programmers call an ¡°unmistakable similarity¡± to the original.
The program, developed by computer scientists in Israel, is based on the responses of 68 men and women, age 25 to 40, from Israel and Germany, who viewed photographs of white male and female faces and picked the most attractive ones.
Scientists took the data and applied an algorithm involving 234 measurements between facial features, including the distances between lips and chin, the forehead and the eyes, or between the eyes. Essentially, they trained a computer to determine, for each individual face, the most attractive set of distances and then choose the ideal closest to the original face.
They ran the photographs of 92 women and 33 men through the engine, creating before and after shots. Changes were made only to the geometry of the faces; unlike the digital retouching done for fashion magazines, wrinkles were not smoothed and hair color was not changed.
The research, published in the August proceedings of Siggraph, an annual conference on computer graphics, is one of the latest studies in a growing field that merges beauty and science.
Studies have found there is surprising agreement about what makes a face attractive. Symmetry is at the core, along with youthfulness and clarity or smoothness of skin. There is little dissent across cultures, ethnicities, races, ages and genders.
Yet, like other attempts to use objective principles to define beauty, this computer program raises complex questions about the perception of beauty and a beauty ideal.
To what extent is beauty quantifiable- Does a supposedly scientific definition merely reflect the ideal of the moment, built from the images of pop culture and the news media?
¡°How can they prove it-¡± said Lois W. Banner, a historian who has studied changing beauty standards, referring to scientific efforts to define attractiveness. ¡°They are never going to locate it on a gene. They are never going to get away from the cultural influence.¡±
Tommer Leyvand, who developed the software with three others at Tel Aviv University and who works for Microsoft in Redmond, Washington, said the goal was not to argue that the altered faces are more beautiful than the originals. Instead, he said, it was to tackle the challenge of altering a face according to agreed-upon standards of attractiveness, while producing a result that left the face completely recognizable, rather than the product of cosmetic surgery or digital retouching.
He suggested there were practical applications for his software, including advertisements, films and animation. He also said he had heard from plastic surgeons interested in the software.
While several psychological studies suggest that perceptions of beauty and attractiveness tend to be universal, critics of that work say it is debatable whether a person¡¯s beauty is actually enhanced by such changes. Character can be lost. The quirky may become plain.
When Mr. Leyvand put a photograph of Brigitte Bardot through his program, her full and puckered lips were deflated, and the world-famous beauty seemed less striking - less like herself. By contrast, the before and after shots of the actor James Franco were almost indistinguishable, suggesting his classically handsome face is already pretty perfect.
Martina Eckstut, 25, an account executive for Kay Unger New York/Phoebe Couture, volunteered to be photographed and have her image beautified by the program. She said she was struck by how different she looked in the second shot.
¡°I think the after picture looks great, but it doesn¡¯t really look like me at all,¡± she said in an e-mail message. ¡°My entire bone structure, face shape and eye size is different, and my lip color looks changed as well.¡±
She added, ¡°I would like to keep my original face.¡±
After viewing the before and after photographs of anonymous subjects in Mr. Leyvand¡¯s research paper, Dr. Banner, who is a professor of history at the University of Southern California, said the original faces were more attractive. ¡°Irregular beauty is the real beauty,¡± she said.