Sorry for the extremely delayed reply, HarryFilm, before Xmas I had a busy time...Your printing recipe looks quite well elaborated, thank you very much. In fact, my wife used a German professional printing service, and their printer software seems to turn her 12 mp files in high res images with some comparable tricks - without producing visible artifacts. The results were really impressive. Well, today's smartphones demonstrate that heavy-sided algorithms can produce quite useful images out of tiny sensors with very small pixels and often not so brillant lenses. The cost of adding "information" to low quality raw images, of course, is that those algorithms sometimes create very strange artifacts.
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Since MOST cameras are actually pretty good these days, it's now up to the printers themselves, where almost ALL now have great error-diffusion based rendering. We have 48 inch wide Epson, Canon and OCE (a division of Canon) to do our large screen prints. At 2400 DPI that is about 600 lines per inch using CMYK or about 400 LPI using 4-colour, 6-colour or 8-colour inkjets.
We have found that by using a fancy Fractal Resizer (we designed our own!) with the very advanced edge detection and object recognition to scale objects, it STILL keep edges razor sharp. We can resize almost ANY image by up to 4x on each axis and get more-than-decent result for bus-poster work or we can merely DOUBLE the resolution on the X and Y axis to get a SUPERB premium glossy magazine quality result. This means our older 8-megapixel pro cameras from 10 years ago (they still work!) can give us 32 megapixels and our high end 1Dx2's will give us 80+ megapixels, and our unreleased 50 megapixel monsters will now give us 200 megapixels! What WE HAVE BEEN DOING is finally coding the "Fractal Resizer" into a CPU chip directly so that ALL our new cameras and computers will have it built-in for real-time or near-real-time SUPER-HIGH-QUALITY image scaling!
Live Fractal Resize on a camera ALSO acts as a form of 1.5x, 2x, 3x and 4x digital zoom! We HAVE TRIED it up to 8x on each axis but it softens edges a tad bit too much for my tastes BUT for some people it may be perfectly acceptable depending upon your application! 4x resize on each axis is the upper limit in my opinion for HIGH QUALITY SCALING results!
Fractal Resize is the BEST resize algorithm out there and so long you work within it's parameters and do ONLY 1.5x, 2x, 3x and 4x resize on the X-axis, you WILL get excellent results! The printers will take care of the rest of the quality issues by distributing any basic/intrinsic image capture errors out to other pixels using simple error diffusion which TRICKS the human eye to thinking there is more resolution than there really is.
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