As we noted in our original commentary on the printer, Epson developed Radiance in conjunction with the Munsell Color Science Laboratory at the Rochester Institute of Technology. At its most basic level, Radiance deals with the issue of how colors in a photo are represented on the printed page. When you’re printing, each color in a photo—usually represented as RGB (red-green-blue) data—must be translated into a color that the printer can reproduce, and it’s extremely important that each color is represented as closely to the original as is possible.

These days, with six-, eight-, 10- and even 12-color ink sets, the colors—or gamut—a printer is capable of producing, has increased significantly, but they still come up short compared with what the human eye can discern, or even the color range that can be captured by a digital camera sensor. Today’s high-end photo printers come very close, but for many professionals, they still don’t come close enough, and the printer companies continue to work on technology aimed at produces the perfect print.

Part of the problem is in the translation between the computer and the printer. There’s no single match for each RGB color when you’re printing: there are actually trillions of different ink combinations that can reproduce the same color when you’re working with a six-color photo printer, and those numbers increase exponentially as you add to the number of inks used to print.

In addition, each ink combination has repercussions that affect the colors around it during the printing process. Sometimes, a printer can’t reliably produce a color similar to the one next to it, which can result in things like muddy shadows, fuzzy details, or strange blotches in large areas of similar color (like late afternoon skies).

To get a digital print that captures the essence of a photographic image, you want four key things:

• realistic color that represents the tonal range of the original image;
• minimal grain, with no visible ‘dots’ at a standard viewing distance;
• smooth transitions between colors, which help give a print the feeling of continuous tone; and
• similar color when viewing an image under different lighting conditions (a problem often referred to as metameric failure).

Epson claims that the technology behind Radiance is largely designed to attack the latter three points—grain, color gradations, and color constancy. Radiance’s color matching algorithms use some fairly complex math, but what it comes down to is that it achieves these things through much more efficient mixing of the inks in the R1900 than in any previous Epson printer.

One slide that Epson shared with us displayed comparable three-dimensional color gamut plots for the older R1800 (which is an excellent photo printer) and the R1900. If you look at the R1800’s gamut plot (on the lower left side of the slide), you’ll see a typical gamut graph, one with bumps and rough edges, which translates to less smooth transitions between colors. The R1900’s plot is much smoother, which should translate in real life printing into better color.

In addition to better color transitions, Radiance should also help with metameric failure, where the eye
detects a shift in color when viewing a print under different light sources. This issue, which was one of the drawbacks in the first generations of pigment inks, has generally lessened as the ink technology has gotten better, but it can still be a problem. Patrick told us that some of Radiance’s color matching capabilities were designed to further minimize these effects, and inks are mixed to produce the best combination for achieving neutral tones in an image.

This isn’t to say that Epson’s competitors don’t care about the mixing of inks; we’re quite sure they do, even if they aren’t trumpeting their technology publicly. (We think this is part of what HP is talking about with DreamColor, but they seem to be more interested in it as a marketing point than actually explaining the technology behind it.) But we are in a time when the leaps in print quality are much less apparent to the naked eye than they were five years ago. As a result, when we see new printers that purportedly offer “better” prints than the ones that came out only a couple of years ago, it’s hard to get a bead on where the important advances are. Understanding even a little bit more about the technology behind some of the buzzwords can go a long way in helping you evaluate printers, especially if you’re looking to produce salable, archival digital prints.

In the end, the proof is always in the print. We’ll soon get a chance to see how the R1900 does on this front, but we do expect to see some improvements over previous technology that was darn good to begin with.

Epson should be posting a short video about Radiance in the next few weeks, but you can see a little bit about the technology by clicking on the Interactive Tour button on the R1900 home page.

Epson also ships a few printers with both FireWire 400 and USB 2.0 interfaces, notably the Stylus Photo R1800 and R2400, and some of Canon’s higher-end printers have FireWire instead of USB interfaces. We’ve had a few people ask over the years if there was any advantage to using one or the other port, so while we were running some speed tests on a group of printers here in the office (for an upcoming round-up), we ran some tests on an R1800 and a series of 300-dpi photos. The result? No difference at all, from a borderless 4- by 6-inch image all the way up to an expansive 12- by 18-inch print.

The results (shown in the tables below) really aren’t that surprising: USB 2.0 has theoretical throughput speeds (480 Mbit/sec) that are slightly higher than FireWire (400 Mbit/sec), although USB 2.0 tends in practice to be a bit slower for things like file transfers between disks (when other factors are equalized). In this case, even with a 300-dpi file, you still aren’t throwing that much data down the data pipe to the printer.

While this was one printer from one vendor, we’d imagine that the results would be pretty similar across the board for the R2400 and other dual-FireWire/USB printers. In the end, choose the interface that works best for the ports you’ve got available.

R1800: Firewire vs. USB (better print quality)

[All times in minutes; print sizes in inches. Tests run from a MacBook Pro, with Mac OS X 10.5, Adobe Photoshop CS3. File resolution was 300 dpi at the print size. Three trials, averaged.]