From: HJswim2@aol.com Date: Sun, 28 Apr 2002 10:15:10 EDT Close, but no cigar. With Epsons, the higher, first dpi number refers to the vertical axis, the lower number is the horizontal. No, the first number refers to the horizontal DPI and the second refers to the vertical. So 1440x720 means 1440 dots per inch in the horizontal direction (parallel to print head travel) and 720 in the vertical direction (parallel to paper travel). Increases in vertical resolution are achieved primarily by speeding up or slowing down the paper transport (also called motor-stepping) so you can pack more dots in a given amount of vertical space. It's not strictly speaking the *speed* of paper transport, but rather the exact distance that the paper is transported between print passes. No current Epson printer actually has nozzles spaced closer than 1/360" apart, and most of them have the color nozzles spaced 1/120" apart. However, the stepper motor that positions the paper can be addressed to 1/720" in most cases (1/1440" on the C80 and probably the C70, and on the 950 and 2100/2200). (Yes, the C80 can do 1440 DPI vertically. Printing the CUPS test pattern, which includes a circle of radial lines spaced 1 degree apart, is an excellent demonstration of this. Under a loupe, the stair stepping is clearly more evident at 1440x720 or 2880x720 vs. 1440x1440 or 2880x1440. While the 3 pl dots are too large to take full advantage of 2880x1440 resolution -- that requires 2 pl drops -- having a more balanced resolution is advantageous when printing very fine detail.) Horizontal resolution is increased by other techniques including variable droplet sizing and droplet offsetting, which also relates to motor stepping. Variable drop sizing has nothing really to do with horizontal resolution (or vertical resolution, for that matter). It's simply a way to print more and smaller dots (hence smoother texture) at low resolution, improving image quality in highlights without requiring extreme precision in head or paper positioning (which increases cost and print time). At 2880x720, 1440x1440, and 2880x1440, the smallest (3 or 4 pl) drops are sufficient to completely fill the page even with glossy paper, even though variable drop size mode has to be used to accomplish that. With the exception of the Stylus Pro printers, no single drop size Epson printer can actually place consecutive dots more closely than 1/360" (or 1/720" in single drop size mode) and no variable drop size Epson printer can do better than 1/720". However, as you note, the positioning for the motor allows addressing to 1/1440" or 1/2880" on all current Epson printers; only a few very old ones are unable to do 1/1440". So each row actually has to be printed in multiple passes. The combination of the multiple passes required to fill the page horizontally and vertically is called "weaving"; it's discussed extensively in the Gimp-print documentation, and one of our papers on it is on Alan Womack's web site. -- Robert Krawitz <rlk@alum.mit.edu> http://www.tiac.net/users/rlk/ Tall Clubs International -- http://www.tall.org/ or 1-888-IM-TALL-2 Member of the League for Programming Freedom -- mail lpf@uunet.uu.net Project lead for Gimp Print/stp -- http://gimp-print.sourceforge.net "Linux doesn't dictate how I work, I dictate how Linux works." --Eric Crampton - Turn off HTML mail features. Keep quoted material short. Use accurate subject lines. http://www.leben.com/lists for list instructions.