I've been terribly slow in turning my photos from our trip to Kerala into presentations, either web or printed.
Last week I arbitrarily started on a scrapbook based on the photos I took around Kochi's Chinese Fishing Nets. When I printed the first photo at a modest 8" width, I was dissapointed to see that it wasn't pleasingly sharp.
Where's the problem coming from?
I used Kodak SW-100 film, which has very fine grain, a Canon 100-400mm lens with image stabilization, scanned the slide w/ Nikon Super Coolscan 4000's maximum resolution (4000 dpi), did next to no modifications in Photoshop, and printed it out with high resolution on the Epson 2100.
All of those steps were reasonable; where did the workflow break down and give me medicore sharpness?
Start with the source. I checked the slide with a 4x loupe. It looked quite sharp; an excellent image. But 4x isn't much amplification. So I dragged out my Leica Pradovit slide projector and viewed the slide as a three-foot wide image. There was the problem! The image just lacked natural sharpness to begin with. In low afternoon light I'd been standing 50 feet away. Although the image is ok, it's not tripod-sharp.
Comparing the print and the digital image of the slide to what I was viewing on the projector screen, the sharpness complaint was clearly originating with the photo, not some later step in the workflow. (This is not to say that I'm not introducing sharpness problems later on in the chain, just that the source image was the pareto cause)
Correcting the image
So to make this a presentable image, I'm going to have to use Photoshop's sharpening capabilities. There are scores of lousy, conflicting tutorials presenting a huge gamut of techniques ranging from super-simple to enormously tedious.
So my current project is to figure out the right way to sharpen this image into its most presentable state.
Resolution
Almost universally, tutorials have warned to apply the unsharp mask on an image that is already adjusted to the final output resolution of the printer.
Ok. Fine. What should that be, then?
Epson says my printer has maximum resolution of 2880x1440 dpi. So this is suggesting that the dots are twice as wide or twice as tall? Why is its printing resolution an area unit (2880x1440) when the Nikon Super Coolscan 4000's resolution a one dimensional unit (4000 dpi) ?
Photoshop :: Image :: Image Size also presents resolution as a one dimensional unit. (in the case of my scanned image, it calls it '4000 pixels per inch')
My pessimistic guess is that I cannot even assume that Photoshop's "Pixels per inch" is the same as my printer's "dots per inch"
What I need to figure out is the function that maximizes the quality of the Epson printer print, while not creating a needlessly bloated image (where photoshop creates 'fake' picture detail just because I forced it to be a certain resolution) given the following inputs and outputs
inputs
sc_scan_resolution: the resolution I tell the Nikon 4000 (sc) to scan with. (in dpi)
ps_pixel_width&height: photoshop settings under "Photoshop::Image::Image Size" units "pixels"
ps_document_width&height units "inches"
ps_document_resolution: units "pixels per inch"