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Tuesday, November 29, 2011

The Right Resolution

The conventional wisdom says set 300 dpi and forget it, but it turns out that there’s more to optimizing image resolution for fine-art printing

This Article Features Photo Zoom

Figure 10 Detail of the print dimensions and native resolution.

This whole thing really came about when I got a Phase One P65+ medium-format 60 MP digital back. It really ticked me off that all that resolution went to waste when printing smaller images. The capture size of a P65+ is 8984x6732 pixels. To make a print on 13x19-inch paper with a minimum one-inch margin results in an image size of 14.68x11 inches and a resolution of 612 ppi, so why waste it? When Lightroom 3 was being developed, I worked with the engineers to increase the previous hard cap of output resolution from the previous 480 ppi. In Lightroom 3, the hard cap is now set at 720 ppi.

I chose an image whose native resolution at the print size of 6.34x9.5 inches would be 432 ppi. The image was captured with a Canon EOS-1Ds Mark II with a 100mm macro lens (Figs. 9 and 10).

In the Print Job panel, I checked the Print Resolution option and entered 720 ppi in the field. You'll note that a warning sign shows up. When you select the maximum resolution, Lightroom feels compelled to warn you—if you click on the warning, you'll get the dialog box shown (Figs. 11 and 12).

Figure 11 Setting the print resolution to 720 ppi in the Print Job panel.

In the Epson 4900 print driver, I checked the option for Finest Detail. This makes the print driver report to the pipeline as a 720 dpi device. Unlike the lower-resolution printing, when using Finest Detail for maximum quality, I also suggest printing in unidirectional mode. In the Canon print driver, I had already been using the Print Quality set to Highest (600 dpi).

The Results Of The Highest Output From Epson And Canon
The prints of the coins were printed and scanned in the same way as the previous tests. The magnification is 10.66x life-size. The differences between the native resolution and the upsampled resolution with Finest Detail on are pretty undisputable. Upsampling to 720 ppi in Lightroom and using the Finest Detail setting in the print driver produce a much-improved result. Whether this is due to the upsampling or the use of the Finest Detail setting, or a combination of both, I don't know. What I do know is that looking at the prints on my viewing box, even without a loupe, I could see the improvement.

Figure 12 The Lightroom warning about high resolution (I ignore it).

The differences on the Canon prints between native resolution and upsampled resolution aren't quite as noticeable. The upsampled print is smoother without some of the jaggies seen in the native resolution print. I still think the output from the Canon is improved by upsampling in Lightroom before printing (Figs. 13-16).

The Bottom Line
The bottom line is, if the image you're printing to a high-end inkjet printer has a native resolution at the print size of less than the printer resolution, upsample to the printer's dpi. In the case of Epson, that's 360 dpi, and it's 300 dpi with Canon and other printers with similar print heads. If the native resolution is above the resolution, upsample the image to the higher reported resolution of the printers (720 ppi for Epson and 600 ppi for Canon). In the case of the Epson line, also check the option for Finest Detail.

Figure 13 Epson output at native resolution with Finest Detail unchecked.	Figure 14 Epson output upsampled to 720 ppi with Finest Detail on.
Figure 15 Canon output at native resolution.	Figure 16 Canon output upsampled to 600 ppi.