Tuesday, May 22, 2007
The Art Of The Up-Res
Getting beyond the limitations of your camera's native resolution is an art and a science
Viewing Distance: The Elephant In The Room
When you consider the intended viewing distances of standard print sizes, fortunately, you find that you often won't need to do a lot of interpolation for standard prints. Below are my recommendations for various print sizes and their “normal viewing” distances.
8x10 Prints or Smaller
Image Resolution: 360 to 480 ppi
Printer Resolution: 2880 dpi or above
11x14 to 13x19 Prints
Image Resolution: 240 to 360 ppi
Printer Resolution: 1440 dpi
16x20 Prints and Bigger
Image Resolution: 180 to 240 ppi
Printer Resolution: 720 to 1440 dpi
Photographers have this annoying habit of looking at really big prints from mere inches away—just to see if there's any tell-tale digital artifacting in the digital print. If your print viewers are photographers, save yourself the grief and pretend every image needs to be output at 360 to 480 ppi at 2880 dpi or above, even if it's a 44x66-inch print!
How Big Is Big?
How big can you make a digital capture? Assuming optimal technical aspects such as capture sharpness, lens quality and other photographic factors, you easily can achieve a 200% up-res interpolation, and with proper processing, upward of 400%. Wanna know how? Well, it's sort of magical, and there may be a degree of, well, cheating involved.
It's possible to enlarge a well-photographed image 400% and sometimes even more. In these screenshots, Schewe used Bicubic Smoother to interpolate a 47.5-megabyte file up to 760 megabytes.
As before, the image is processed through Camera Raw with no sharpening, no luminous noise reduction and the default 25 color noise settings.
Next, the Image Size was used with a setting of Bicubic Smoother and either 200% or 400% set as the up-res interpolation (Figure 7).
After up-resing, and depending upon the amount of up-resing, a series of image-sharpening routines were deployed. Using PhotoKit Sharpener, I combined a Digital High Rez Capture Sharpen to apply an initial sharpening. I applied a Creative Sharpen phase of Super Sharpen 1 and 2, followed by Super Grain 1 or 2. Why grain? Isn't that cheating? Yes, it is, but all's fair in love, war and image interpolation (Figure 8).
By adding a degree of what PhotoKit Sharpener calls Grain, I'm actually adding a very slight high- frequency texture on top of the resultant interpolation and additional sharpening. This has the effect of breaking up the image pattern in a manner that makes the subsequent image a bit more “photographic” or less smooth, which is a tell–tale clue to a digital print of an up-resed image.
On top of the sharpening and grain, I added an additional Output Sharpening layer optimized for the line screen ruling of 150 lpi and the image resolution I supplied to the magazine of 300 ppi.
We're accustomed to seeing a certain amount of “break-up” in really big photographs. Part of the art of making a very large digital image lies in mimicking this look. Using the PhotoKit software that Schewe helped develop, he applied sharpness and then an amount of simulated grain, which helps make the image appear “photographic.”
Figure 9a shows the native resolution 16-megapixel capture at a screen zoom of 200%. You'll note that without interpolation, the image looks pretty ugly. Were I to try to print this at an output size of 66x44 inches, the image resolution would only be about 75 ppi, well shy of human vision. The result would be a very pixilated output.
Figure 9b is the by-product of doing a 200% up-res interpolation and the resulting sharpening and grain. This time, the screen zoom is at 100%.
The interpolation has added enough created pixel resolution to no longer look extremely pixelated. This interpolation would result in a suitable output at about 33x22 inches at 300 ppi.
Finally, Figure 9c is a 50% screen zoom of the 16-megapixel capture up-resed 400% to a final size of 66.56x44.373 inches at 300 ppi. By viewing the image at a 50% screen zoom, it's a fair representation of what the image would look like in halftone reproduction, which I admit is somewhat complicated since what you're looking at is a halftone reproduction of a Photoshop screenshot of a digital capture up-resed a whopping 400%.