Huge Art Scans on Location

Note: This is a posting for people in the art reproduction business as well as patrons so portions may be too technical for your needs. If you are an artist that paints huge canvases, and have any questions, please feel free to write

Where do murals begin and paintings stop?

You don’t need a classics studies degree to know that “mura” is Latin for “wall”, so “murals” are wall paintings, right? At UCLA’s “SPARC” (Social and Public Art Rescue Center) the definition is considerably broader. In addition to the preservation of the urban murals which abound in Los Angeles, “SPARC is particularly committed to producing and promoting work that reflects the lives and concerns of America’s ethnically and economically diverse populations including: women, the working poor, youth, the elderly and LA’s newly-arrived and numerous immigrant communities”. This translates into sponsoring new works, often as painted canvases, usually in the grand muralist styles of story telling, and most always BIG.
One such painting, “La Danza de la Tierra” by Professor Judith Baca, co-founder of SPARC, was painted in the tradition and style of Diego Rivera. It was commissioned for a museum in Dallas.
La Danza
"La Danza" by Judith Baca, 180" x 120"

Laying Out the Scans

We were asked to create a “hi-rez” printing file in order to print a full-size canvas reproduction. In the case of copying Ms. Baca’s painting, “hi-rez” meant creating a bitmap document which, when printed full-size, will appear sharp at a near distance, say a foot or so. What will satisfy this? If we were to generate a file to make a 10’ x 15’ print at 300 ppi, it would have to be 54,000 pixels x 36,000 with a flattened file size of 5.4 GB. However, if we dropped the output 180 ppi, we could create a picture 1.96 GB, making everyone happy and is still “hi-rez”. Further, five tiles in each row would yield a generous overlap, an advantage in assembling the image.
But how do we get two rows without losing registration? Answer: by inverting the painting for the second row
La Danza
The actual scans. Note the overlap for tiles

The Set-up in a Tight Space

SPARC’s condition was that we must scan the work in Judith Baca’s studio. Fortunately the studio (30’ long) was exactly twice as long as the painting, so we installed a 30’ long industrial track, so we could shoot them in 2 rows of 5 tiles each, so long a Ms. Baca didn’t mind lag bolts in her wall. She liked the idea, seeing the track installation’s potential for other large works in the future.
The goal for lighting the painting is to create perfectly even illumination across our frame which we calculated to be 67”h x 50”w. This is why our diffusion panels are 72” high. Everyone has their own formula for lighting. I use an incident meter with a flat disc to get within 0.1 f-stop, then use the Better Light software eyedropper as a “spot-meter” to see if further tweaking is necessary. It’s useful to note that we prefer quartz lights for large set-ups instead of our studio North Lights as the quartz instruments have both spot/flood and barn doors to modify and shape the light. We also have tons of them.
Scan setup in Judith Baca's Studio
Inverted Painting. Note the 30" roller track we installed

Post Production: Assembling the Files

There are two basic ways to “merge” these tiles into a seamless single file: the Manual Solution and the Automated Solution, both using current versions of Photoshop and both requiring that the “tiles” be shot perfectly, i.e. uniformly lit, perfectly square, with not lens distortion.
The Manual Solution (called “stitching”) is what I used in the past (from, say, 1990) and still resurect in extenuating situations. In the case of "Danza", I would begin with dragging the 10 scan tiles into a fresh Photoshop doc, align them, carefully create layer masks for each layer. When this is done to our satisfaction, we flatten the file, and have a beer. This process could take an hour or more.
The Automated Solution involves a Photoshop utility called “Photomerge” that has been around since CS5 (2012). It was created to create circular panoramas, which is obious when you launch this utility. BUT if you have photographed (scanned) in the same flat plane as we did, it (magically?) merges them into a perfectly seamless single flat file in the space of 5 minutes. It does this by “looking” at the areas of overlap between the files to identify unique identical details (called “anchor points”). If enough anchor points cannot be found, you get an error message. At this point, it is handy to know how to put it together manually.
Gourmet Mexican Restaurant
"La Danza"
This print is hung at the Casa Linda restaurant, Venice CA.