Dr. Yang Cai spent many Sundays last fall walking through the cemetery of Old St. Luke's Church in Scott.
He would pass the remains of William Lea, a French and Indian War veteran who donated the land for the burial ground, and Capt. David Steel, a Revolutionary War veteran who belonged to one of Pittsburgh's founding families.
But Dr. Cai wasn't there to honor distant kin or dignitaries. Instead, the Carnegie Mellon University senior computer scientist was there to shed light, literally, on those and other longtime occupants of the cemetery.
Using a small scanner and a digital camera, he worked to retrieve tombstone information erased by 243 years of harsh weather, acid rain and pollution, the scourge of sandstone memorials.
The computer scientist's high resolution, three-dimensional scans of the grave markers have retrieved names, ages, dates, epitaphs and other valuable information that was illegible from 30 tombstones. And Dr. Cai hopes to create a virtual tour of the cemetery for the church's Web site.
The digital scans "are revealing data that I've never seen with my eye," said the Rev. Richard W. Davies, vicar of Old St. Luke's since 1989.
Dr. Cai, who spent last summer in northern Italy documenting rock art with college students from all over the world, learned about Old St. Luke's Church from his co-worker, Michael Stroucken, a senior programmer who passes it on his daily commute.
The potential for unearthing information with this technological version of gravestone rubbing thrills historians and genealogists, who often visit Allegheny County's 400 cemeteries.
"I think that this is going to interest a lot of people. The fact that we can take a completely illegible gravestone and utilize this cutting edge technology to make it readable again and to give that information back to people, I think, is amazing," said Marilyn Cocchiola Holt, program chairwoman for the Western Pennsylvania Genealogical Society.
The scanning system Dr. Cai uses reconstructs the image using digital lighting and filtering. The special filter delineates the curved and linear features on a tombstone's surface. Then, the computer software strips the image of any color, a step that improves the clarity and quality of the image.
"The software is good at filtering and rendering the massive data, but human experts are good at reasoning, finding the errors and connecting the dots," Dr. Cai said.
Father Davies has devoted 20 years of his life to preserving the church and its history.
"Only the sandstone markers are illegible. The marble and granite ones are in great shape. The blessing for us is that he's chosen us and that's our reward for being there. His reward will be what he'll do with the technique," said the retired priest, who lives in Mt. Lebanon.
With enough money and manpower, Dr. Cai believes this technology could be made available to amateurs in about two years. The software he has developed also has potential applications in medicine, geography and security checkpoints.
Deciphering these tombstone inscriptions began with pointing a scanner and downloading the images to a laptop computer.
But Dr. Cai worked closely with Father Davies to double-check the information so that it jibed with what is known about early settlers resting in the cemetery. The vicar is the author of a history of the church, its burial ground and garden.
Tombstones yield far more than names and dates, Ms. Holt said.
"People find so much information. A tombstone can have a profound effect on people who are looking for information about their family. It has genealogical information. It can give medical history if it says that a person died of a particular disease."
At the Association for Gravestone Studies in Greenfield, Mass., Ann Myles, a staff member, echoed Ms. Holt's enthusiasm.
"It's going to give us access to history and cultural information that we weren't able to get before," Ms. Myles said, adding that the organization, which preserves and interprets tombstones, has 1,200 members.
About 22,000 cemeteries in the United States have an address and phone number, but Bob Fells, a spokesman for the International Cemetery and Funeral Association in Sterling, Va., says the nation probably has 40,000 or more. It's not certain because many cemeteries have religious affiliations or are family plots.
Marilyn Evert, director of development for Homewood Cemetery Historical Fund, which pays for restoration projects at Squirrel Hill's Homewood Cemetery, said Dr. Cai's work is terrific.
"This is going to solve a lot of problems and answer a lot of questions that couldn't be answered before," Ms. Evert said.
Correction/Clarification: (Published Jan. 12, 2008) This story as originally published Jan. 11, 2008 about computer scientist Dr. Yang Cai's use of digital technology to retrieve information from illegible grave markers incorrectly stated that he has created a virtual tour of the cemetery at Old St. Luke's Church in Scott. Dr. Cai plans to build a virtual tour of the cemetery for the church's Web site in the future.
Marylynne Pitz can be reached at firstname.lastname@example.org or 412-263-1648.