>From a practical standpoint, I have noticed that images with fine parallel >lines will create a wavy pattern on Epson printers when the file's resolution >is not a divisor of the printer's resolution. Resampling the file upwards or >downwards to the closest divisor completely eliminates the patterning.
I have noticed this behavior in six printers over about four years. It isn't common, but it will crop up from time to time. I noticed it repeately over the years in group photos where someone was wearing plaid. Also saw it in the wires of a suspension bridge once. This is coming from my lab work -- different clients, different cameras / scanners / formats. The behavior was noted in the manuals for the Epson 7500 and 2200, if I recall correctly. -Aaron -----Original Message----- From: "Patrice LACOUTURE (GMail)" <[EMAIL PROTECTED]> Subj: Re: PESO: Another Pano Date: Sun Apr 23, 2006 3:41 pm Size: 3K To: [email protected] Hi! Most inkjet printers, including cheapo entry-level ones, advertise very high resolutions like, 2880 or 5600 dpi... In fact, these figures give the positional accuracy of individual ink dots. At this native resolution, there are a very limited number of colours: each position on the paper either receives, or not, a drop of every ink color. With a 4-inks printer, each point can get: - nothing (white) - black dot - cyan dot - magenta dot - yellow dot - cyan + magenta (blue) - cyan + yellow (green) - magenta + yellow (red) ... for a total of 8 colors (black can't be mixed with other colors, and mixing C+M+Y doesn't make much sense: would be a "dirty black"). These are theoretical figures, and do not consider blending and such. For printers with more ink colors, do your own math. This isn't much, and to get continuous tones (256*256*256=16M colors), the printer must use dithering, by arranging these 8 colors in a pattern, that look like a continuous tone pixel to the naked eye. Wikipedia will explain this much better than I could ever do: http://en.wikipedia.org/wiki/Dither#Digital_photography_and_image_processing or http://tinyurl.com/mvwuf In short, the greater the difference between the image resolution and the medium (printer) resolution, the better color approximation one can get. With 5000+ dpi, and a 300dpi image, each pixel is 16 dots wide on the paper, which leaves plenty of room to represent accurate color. With ordered dithering technique, this ratio between the print resolution and the image resolution is fixed: each image pixel will be exactly and always 16x16 dot positions for instance, and it is important to stick to fixed resolutions. With error diffusion techniques, there is no such restriction, and a great deal of adptation. Sharp edges can even use higher resolution than continuous areas, which need less definition, but greater color accuracy. In theory, the precision of continuous tones is not limited, while the full native resolution is available for a black & white edge. Nowadays, error diffusion is commonly used for photo printing, and ordered dither is only used for computer graphics, charts, etc... For a photographer, the bottom line is: - For inkjet printing, don't care about your image's resolution. 234.56dpi is fine, anyway the printer is 5000+ dpi and does error diffusion. - For continuous tone printers, ask the native resolution and stick to it. These printers (DLP, laser...) can print directly in continuous tone, but have a "low" native resolution (300 or 400dpi). If you do 234.56dpi, it would have to be resized to 300 or 400dpi first, and you don't control the quality of this resize. Regards Patrice Shel Belinkoff a écrit : > What does all that mean? > > 5000+ dpi ... seems like a lot, perhaps excessive. Can you explain? > > What's an "error diffusion pattern?" > > What's "DLP technology?" > > Shel > >>> As it is inkjet, with probably 5000+ dpi dot pitch and error diffusion >>> patterns, there is no real need to stick to the machine's hardware >>> resolution, like with digital minilabs based on DLP technology. I don't >>> seriously intend to print anything this size anyway! >>>
