> Jorge Parra > APA/ASMP wrote: > Subject: [PRODIG] Re: In Deep Digital Trouble > Interesting to mention here that a colleague in NY , just wondering why > should Canon use 180ppi as the "reference" resolution of all the images > coming out of their cameras, he decided to run a proof test at 180 ppi > and > results were astounding to him, leading to the apparent conclusion that it > may be possible the the 300 dpi rule applied to files from scanners can be > broken down t 180dpi on files from digital cameras, and 225 given > absolutely comparable results than 300 dpi files. Should that be the case, > then you won't have to upsize that much anyway. > This is not surprising because of the way files are rasterised for printing. For a 150 lpi (lines per inch) screen a 150 ppi (pixels per inch) image is needed BUT when sampled for rasterising it is inevitable that some pixels will be sampled twice and some missed! Result is poor reproduction. Make the original image 300 ppi and you guarantee that good sampling will result in the best possible resolution of detail in print. In fact I think it take a very fussy printer with a loupe to tell the difference between the result from a 225 and a 300ppi original when printed at 150lpi. My own belief is that the 'quality' of an original makes more difference than simple dpi.
Assuming the printers will use a 150line screen have you considered preparing the file at 150ppi and then enlarging to 300ppi using PS 'nearest neighbour' setting. My tests in PS suggest that this will avoid the 'softening' of some details that bicubic can cause as it interpolates. Most inkjet printers use stochastic (diffused) screening rather than the fixed screening of most image setters and if printing at 1440dpi are in theory screening at 90lpi (one cell of dots 16x16 creates one pixel with a value between 0 and 256). I suggested a while ago that anyone who thought different should try printing a lens testing chart or similar on their inkjet. I have now done that and surprised myself! My Epson 1290 can (just)resolve 1 pixel line pairs at 360ppi, though in truth the white gaps between the lines of ink are only just discernable with a magnifier. 180ppi is the limit of my eyes on photo paper. Assuming they actually produce 256 levels in each colour they are achieving the theoretically impossible. Does anybody know how? Paul Lawrence --- Outgoing mail is certified Virus Free. Checked by AVG anti-virus system (http://www.grisoft.com). Version: 6.0.461 / Virus Database: 260 - Release Date: 10/03/2003 =============================================================== GO TO http://www.prodig.org for ~ GUIDELINES ~ un/SUBSCRIBING ~ ITEMS for SALE
