Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!zaphod.mps.ohio-state.edu!unix.cis.pitt.edu!dsinc!bagate!cbmvax!johno From: johno@cbmvax.commodore.com (John Orr - CATS) Newsgroups: comp.sys.amiga.graphics Subject: Re: WANTED: Full page paint program Message-ID: <21587@cbmvax.commodore.com> Date: 15 May 91 15:26:11 GMT References: <16281.2828002a@levels.sait.edu.au> Reply-To: johno@cbmvax.commodore.com (John Orr - CATS) Organization: Commodore, West Chester, PA Lines: 31 In article holgerl@amiux.agsc.sub.org (Holger Lubitz) writes: >In article bobl@graphics.rent.com (Bob Lindabury - SysAdm) writes: >>Ah...well, you can just use DpaintIII. Version 3.25 allows just >>about any size page and I'm sure you can do an 8x11 page quite easily >>if you have the ECS Agnus chip. > >I disagree. If we have 8x11 at 300 dpi, that's 7.920.000 pixels. >Divide this by 8 to get 990.000 bytes FOR A SINGLE BITPLANE. > You assume that you are printing screen pixels as individual dots on the printer. If dithering is required to match the ilbm's colors, you will not get a one-to-one corespondence of screen pixel to printer dot. For example, a black and white 300 dpi printer can only print 300 black dots per inch, it cannot print grey scale dots. To get a grey shade requires dithering, which reduces the apparent number of "dots" per inch because it takes several printer dots to make up one screen dot. In a simple dithering scheme, to get about four grey shades from a B&W 300dpi printer, it would take a 2x2 grid of printer dots to make up a one grey scale "dot", reducing the resolution from 300dpi to 150 dpi. Using the same scheme to get about nine grey shades would require a 3x3 grid and would reduce the resolution to 100dpi. Smarter dithering methods will yield better results, but the point is that because you are probably dithering, your one pixel on the screen will correspond to several on the printer. --John