On Tuesday 20 May 2008 09:55, Patrick Moore wrote: > It seems that today DPI for resolution is used worldwide by the computer > industry, including printers. My googling in the last day has turned up an > alternative, simply to specify pixels in micrometers. However, I fear that > this alternative will require an ISO standard and decades before it becomes > widely adopted. See these links: > <http://www.iol.ie/~sob/tm/index.xhtml> > <http://www.cl.cam.ac.uk/~mgk25/metric-typo> > <http://en.wikipedia.org/wiki/Metric_typographic_units>
There are four separate issues here: the size of a printed pixel, the unit used by PostScript, the dimension of a letter to use as the font size, and the set of font sizes available in some software. For which dimension to use, see the links. Plotters are, and have been since I was a kid, made with a resolution that is a round submultiple of 0.1 mm, typically 0.025 mm. I don't know if the physical resolution of inkjet plotters is a submultiple of 0.1 mm, but I do know that the HPGL driver at my office, used with the last version of AutoCAD that was available for SCO, expresses distances in 25 µm units. This means that both inches and millimeters are expressible as integers, but the point is not. PostScript is perfectly capable of scaling by arbitrary factors, but if you want to make a document in millimeters, you have to specify it at the top of each page. To fix this, Adobe and whoever else writes PostScript-handling software have to do three things: 1. Add a version of the PS-Adobe header that says that a document is metric. 2. Add a flag to the PostScript interpreter (which ignores DSC) to specify millimeters. 3. Modify the software to recognize the new header, so that BoundingBox values in millimeters are computed correctly. For a set of font sizes, I suggest using the musical scale. Many ratios in it are close to ratios of small integers, and the ratio between two paper sizes such as A1 and B1 (before rounding to millimeters) is three half steps. As PostScript can scale by arbitrary ratios, this can be implemented independently of printer resolution. Pierre
