Hi folks,
Sorry I'm late to the party here. Lot's of things to address so I won't comment on each and every post sofar, but I'll try to condense things into the most relevant issues one needs to consider. Also note that quality improvements may be small (but they are there nevertheless) when pushing the printer to its limits.
First of all. Current inkjet printers work with drivers that use a few fixed (due to hardware) 'native' resolutions. Canon and HP printers typically offer 300 or 600 PPI resolutions, and Epson printers use 360 or 720 PPI.
The Epsons need to have the 'finest detail' option switched on in the driver dialog, otherwise all input will be resampled to 360 PPI, where as the Canon drivers usually are more clear in what they are going to do.
There may be (on some printer models) some driver options suggesting e.g. 1200 or 1440 but those are typically DPI settings, IOW adjustments of the dot or droplet dithering algorithms, used to dither and weave the droplet patterns in order to create intermediate/mixed colors from only a few ink colors and a print medium's background reflection.
Any output resolution (PPI = number of pixels divided by the output size in inches) that is not an exact match to those 300/360 PPI or 600/720 PPI, will be resampled by the printer driver. On Mac computers resampling routines from the OS are used, on Windows systems the driver resamples itself. However, the resampling algorithms used are built for speed, usually bi-linear resampling is used (and maybe/unlikely bicubic at best), not for quality.
That's why it's better to resample
before sending the data to the printer, which allows a) to use better algorithms, and b) to
use output sharpening after resampling which potentially makes a huge difference in perceived quality. Especially when using the highest resolution settings, i.e. 600/720 PPI, we have lots of pixels which can be pushed really far without creating visible artfacts at normal viewing distances. Human visual acuity is on average close to the 300/360 PPI settings when detail is viewed at reading distance and at good lighting levels. However, Vernier resolution offers much higher acuity clues which human vision will appreciate. Therefore, the highest resolution settings will make a difference
if the output after resampling is properly sharpened.
There are also resampling applications that actually add resolution beyond what the original data has to offer. This typically results in edge detail that is narrower/sharper than the resampled data would allow with regular upsampling. "PhotoZoom Pro" and "Perfect resize" are two of such stand-alone applications that also manifest themselves as (automation) plugins when Photoshop is used as a host program.
I've done a lot of research and analysis of these printer peculiarities, and discussed matters on another website for those who want more background detail on the underlying principles.
Here, and
here, and
here, and
here, and
here are some links.
The final conclusions are as I laid out above; PPI settings of 600/720 PPI do produce better quality output, if the image has good detail, if the resampling quality is better than what the printer driver does natively, and if one uses good quality output sharpening after resampling the source images to exactly those 600 or 720 PPI in output.
As for software to do the resampling and sharpening, I've found the following options do offer the best workflow/image quality:
1. Lightroom offers reasonably good resampling quality, but is limited (to a few fixed choices) in it's control of what sharpening is used after resampling.
2. Qimage Ultimate offers a superior workflow for printing, and uses very good (proprietary) resampling algorithms. It also offers a very effective automatic 'Smart' output sharpening method which uses another proprietary halo free sharpening method called Deep Focus sharpening (DFS).
3. For those who seek even higher output quality, there are dedicated resampling programs that add resolution (as can be demonstrated by inspecting the resampled data in the frequency domain, after conversion to Fourier space representation).
PhotoZoom Pro by Benvista, and
Perfect Resize by OnOne, are the two more capable ones. One does have to watch out and not exaggerate the amount of resolution that is added, otherwise there will be what I call a visual disconnect between edge detail and lower contrast features.
4. As an overall recommendation to improve image detail, regardless of which output pipeline one is going to use, but also as a general tool for output sharpening, I cannot recommend
Topaz Labs Detail enough. It is one of my 'must use' plugins (usable in virtually all Photoshop plugin aware applications). This plugin does marvels to any image that could benefit from good detail. It can also help to tackle some of the perceptual challenges that stem from viewing image detail at different viewing distances. Images that have been properly processed with this tool, will look good at any distance.
Cheers,
Bart