23 Replies Latest reply on Jul 15, 2016 1:16 AM by Danny Whitehead.

    Printing PS Points VS mm

    De Pascalis Level 1

      I layout and design everything in millimetres, but I use points (pt) for typeface dimensions and stroke widths. Using different units can make the layout process a bit difficult, so I was thinking about using millimetres for stroke widths instead, with a maximum of one decimal place, 0.25pt->0.1mm, 0.5pt->0.2mm, 1pt->0.5mm etc.

      What I was wondering is: are there any possible printing complications when using millimetres and printing e.g. a 0.1mm line which equals to 0.283465...pt, like unsharp lines or ghosting etc.?

      I'm thinking if fractions of post script points behave similar to fractions of pixels (don't go nuts about the pixel comparison, I know the difference), e.g a 1pt line will always print sharp, but a 0.168721...pt line could print differently depending on multiple factors like drivers etc.

       

      Also, are there any possible side effects or complications if I switch to millimetres for dimensioning typefaces?

       

       

      Printing is not my strong side; it's too much to comprehend. It feels like you need a PhD in printing to get the output you want, and that is after you get a PhD in color management.

        • 1. Re: Printing PS Points VS mm
          Derek Cross Level 6

          InDesign will convert measurements automatically. For example, if you're using points for lines and you type in 2mm it will convert it to 5.669pt.

           

          Having said that, it's customary to have page dimensions for documents to be printed to be in inches or millimetres and type and lines to be in points.

          • 2. Re: Printing PS Points VS mm
            De Pascalis Level 1

            Hi Derek,

             

            Yes I know, but I was wondering if fractions of points can have an undesired result when printing on paper. Do some printers or drivers change that point size of 5.669 to the nearest whole number 6 for example? Or are there any other complications that can occur?

            • 3. Re: Printing PS Points VS mm
              Peter Spier Most Valuable Participant (Moderator)

              ALL dimensions, regardless of units, get rounded to the nearest whole dot the printing device produces. High-res devices like commercial image setters are more accurate than low-res devices like a desktop inkjet.

               

              You may get more rounding errors specifying mm, but I doubt you'd notice out three places.

              • 4. Re: Printing PS Points VS mm
                De Pascalis Level 1

                Thanks Peter,

                 

                I can't find what a "dot" is, does a dot have any dimensions before print or is it just location.

                I've always thought that points had something to do with printing and that it was a unit dedicated for that. Reading about points again it seems like it's just another unit of measure, used for typesetting. If that is so, and if points doesent have any more correlations to printing than any other units of measure, then I understand that I can use any unit I prefer.

                 

                So, what is a dot and do I need points?

                • 5. Re: Printing PS Points VS mm
                  Derek Cross Level 6

                  As mentioned, points, ems and picas are measurements commonly used for type sizes, and type measurements such as leading. I strongly recommend you stick with these for documents to be printed as it may cause confusion down the line if you have to liaise with other designers and printers. And use inches or millimetres for page sizes.

                   

                  When placing images in InDesign it's important to have high resolution images, rule of thumb between 200 and 300 PPI (Pixels per inch), Understand the Effective PPI of the image you've placed in InDesign by checking the images in the Links panel. Output to printers is described as DPI (dots per inch). And a further complication, commercial litho printing uses a screen called line screen – around 150 lines per inch for sheet-fed printing on coated stock.

                   

                  If you look these items up online it will explain the, in more detail.

                  • 6. Re: Printing PS Points VS mm
                    Peter Spier Most Valuable Participant (Moderator)

                    Printers use dots of ink to produce the image. Desktop printers these days are typically 600 dot per inch (dpi) so for them a dot would be 1/600" in diameter. An image setter used to make film for offset printing would be in the range of 2800 dpi, so the dots would be about 25% of the size of the dot from your desktop printer.

                     

                    Like pixels in a photograph, you can't have half a dot of ink.

                    • 7. Re: Printing PS Points VS mm
                      Derek Cross Level 6

                      The halftone screen of say 150 lines per inch is made up by the image setter of lots of micro dots that are in the range of 2800dpi

                      Gosh we are really going to confuse the OP:

                      • 8. Re: Printing PS Points VS mm
                        Randy Hagan Adobe Community Professional

                        A "dot", for the purposes of output, is the resolution unit for a given output device -- e.g. the dot for a 600dpi laser printer is 1/600th of an inch.

                         

                        I generally refer to this in terms of image halftones -- I've got a standard explanation of translating pixels vs. (output) dots vs. (printer) spots -- but in this case, we'd be referring to them in respect of how many "joined" output dots would constitute line width. For example, that 2mm-wide line would translate into 5.669 points, or 47.241666... output dots.

                         

                        Fractions don't count, because the output device can't print part of an output dot. It can print one, or it cannot. So that rounds down to 47 output dots wide. Or rounds up to 48.

                         

                        So, literally, you can't print a 2mm line on a 600 dpi laser printer. It's a lie. But it's a very small lie.

                         

                        A 47 output dot line turns into a line that's like 1.98966582 mm wide. A 48 output dot line is 2.032 mm wide line. Your eye will never tell the difference, nor will a ruler placed on the top of it. So it's safe to accept that little lie, that in either case a variation of .04233418 mm between output dots is inconsequential, and in either case it's safe to call that a 2mm wide line.

                         

                        If less than 5 hundredths of a mm is unacceptable, you can make the margin closer by running the job on a 3600 dpi imagesetter. I'd do the math on that, but it'd make my head hurt. I became a graphic designer because I hated math ... though math is still an integral part of the business if I want to be a good one.

                         

                        So accepting these little lies make life a heck of a lot easier, and stops making my head hurt. Hope this helps.

                        • 9. Re: Printing PS Points VS mm
                          Peter Spier Most Valuable Participant (Moderator)

                          Well, you're the one who added halftones to the discussion.

                           

                          For halftones the better term is spots (like pixels is the correct term for images). Halftone spots are made from printer dots, and the number of dots that can be used to create a spot increases as the printer resolution (printer DPI) increases and/or the line screen (LPI) gets coarser (fewer lines per inch). The more dots in a spot, the more shades of gray, or color, can be rendered.

                           

                          Spot size vs. detail and color rendering is always a trade-off. Desktop printers typically have a fixed LPI setting, or perhaps a handful of settings the user can choose, which optimize the output for the best combination of detail and color that the printer can produce. Keep in mind that the values that are lost when you reduce the number of dots per spot are not clustered, but fall through the entire range of 0 -100% darkness, and very few people are able to distinguish 1% changes in value, so until you start losing more than half the potential shades you probably won't notice that as much as you would see jaggies or loss of detail from using a coarser line screen.

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                          • 10. Re: Printing PS Points VS mm
                            rob day Adobe Community Professional & MVP

                            Reading about points again it seems like it's just another unit of measure, used for typesetting

                             

                            That's right, postscript defines a point as 1/72" and it's the default with InDesign. But you can define Points per inch to be whatever you want in Preferences>Units and Increments.

                             

                            Screen Shot 2016-07-11 at 2.41.09 PM.png

                             

                            As others have mentioned the accuracy of lines with no color tint is limited only by the output device's resolution—a typical imagesetter/platemaker will be 1/2400 of an inch. I think you would be hard pressed to see a 1/2400" line without magnification and a typical offset press probably can't hold ink on that line.

                             

                            If the color of the line has a tint, that will introduce a halftone or stochastic screen. A 50% black, .2pt line would no longer be solid, the halftone screen needed to create the tint would turn it into a dotted line.

                            • 11. Re: Printing PS Points VS mm
                              De Pascalis Level 1

                              Thank you all for the detailed answers.

                               

                              I strongly recommend you stick with these for documents to be printed as it may cause confusion down the line if you have to liaise with other designers and printers.

                              I don't mind confusing people down the road, I was originally concerned about confusing machines, or sending the wrong signals to them.

                               

                              I'm familiar with effective resolutions, DPI, PPI and their differences. I just realized that I didn't know what the dot in DPI actually was or if it had any dimension. What I mean with that is; if DPI is measured from center-to-center of the dots, then the dot size can vary for a given DPI and therefore doesn't have any given dimension. At 5 DPI, a dot is placed at every 1/4th of an inch (ex. A & B in illustration below).

                              Or, if DPI is measured from the outer perimeter-to-perimeter of the dots, then the dots will have a definite dimension at a given DPI. At 5 DPI, a dot will be placed at every 1/5th of an inch (ex. C below). That must be extremely difficult to calibrate in a machine and therefore sounds almost impossible to me?

                               

                              DPI.png

                              A & B. At 5 DPI, a dot is placed at every 1/4th of an inch. The dot size isn't exact and could vary from printer to printer.

                              C. At 5 DPI, a dot is placed at every 1/5th of an inch. The dot size is exact and the same on all printers at a given DPI.

                               

                              Since Peter and Randy say that a dot at 600 DPI is 1/600 in diameter, then they must be measured from perimeter-to-perimeter (ex. C), which I think is kind of impressive if printers consistently can keep a size of ink spots that small.

                               

                               

                              Randy,

                              Perfect explanation, it helped a lot.

                              I like to have whole numbers in my dimensioning and settings, that’s why I want to use the same units everywhere.

                               

                               

                              What I don't understand is, if none of these units like points, picas and agates are related to printers, why do we still use them? Why did folks come up with them in the first place, couldn't they have just used other units at hand.

                               

                               

                              But you can define Points per inch to be whatever you want in Preferences>Units and Increments.

                              Why would I want to change this? Very few mentions this setting if I do a search on it.

                               

                               

                              To summarize this thread, assuming example C in the illustration is correct:

                              DPI = Dots Per Inch

                              LPI = Lines Per Inch

                              Dot = the smallest ink building block, its size varies depending on the DPI.

                              Dot size = 1/DPI

                              Spot = ink spot made of ink dots

                              Point = unit of measure, currently ca. 1/72th of an inch

                              Halftone = a pattern made by ink spots, horizontal and vertical distance between spots depends on LPI

                               

                              And the answer to my original question. It doesn't matter which unit of measure I use for stroke and type, all of them will split dots either way, and a dot more or less isn't noticeable anyway.

                              • 12. Re: Printing PS Points VS mm
                                Randy Hagan Adobe Community Professional

                                Just a minor point: dpi output generally doesn't refer to an ink impression on paper, but on laser toner burnt/fused on paper, or an imagesetter photo exposure burning on paper/film/plates. Laying ink down on paper/substrate literally blurs/blends the issue due to the substrate absorbing the ink into the substrate and resulting in dot gain.

                                 

                                Again, this is a little lie, because there is minimal dot gain with parallax between the light/lens/substrate with imagesetters and to an even smaller degree, fusing toner onto paper. But it's minimal to the spread you'll get as paper absorbs ink on press.

                                 

                                As far as using printer's measure -- picas/points -- in the US those measures are still relevant in the printing and publishing industries. Less so as time goes on, as more printers feel comfortable working in inch measures. I can't say how much that is the case out in Metric Measurement Land. Adobe applies that printer's measure affectation as the common unit within InDesign, and translates that measure out into other units universally within InDesign, and to a lesser degree with Adobe Illustrator as well. My guess is Adobe uses picas and points because it allows common translation into inch/metric forms, even if it doesn't report in whole units.

                                • 13. Re: Printing PS Points VS mm
                                  Peter Spier Most Valuable Participant (Moderator)

                                  Dots don't vary in size for any given resolution, and would be most like your example C...

                                   

                                  I would quibble with the last two statements you make above:

                                  Point = unit of measure, currently ca. 1/72th of an inch

                                  Halftone = a pattern made by ink spots, horizontal and vertical distance between spots depends on LPI

                                   

                                  A postscript point is EXACTLY 1/72 inch. The various "traditional" point values used for centuries in various different countries before the advent of Postscript and electronic typesetting are all slightly smaller.

                                   

                                  Halftone spots are all the same size. It's just that they don't fill all the "cells" in the spot to create a lighter shade for traditional halftone screens. Stochastic, or FM screens vary the density of the spots to achieve tonality. Packed together is dark, spread apart is lighter.

                                  • 14. Re: Printing PS Points VS mm
                                    rob day Adobe Community Professional & MVP

                                    Halftone = a pattern made by ink spots, horizontal and vertical distance between spots depends on LPI

                                     

                                    Halftone screens create the illusion of tonality by varying the size of the marks, which are drawn with the smaller printer dots. Stochastic screening creates the illusion by spacing same sized marks. Stochastic screens are less common with offset printing and more commonly used with inkjet printers. Stochastic is better at holding fine detail, but not as good with smooth, noiseless transitions

                                     

                                    So under magnification stochastic would look like a diffusion dither:

                                     

                                    Screen Shot 2016-07-13 at 2.33.25 PM.png

                                     

                                    Halftone dots vary in size depending on the color tint percentage:

                                     

                                    Screen Shot 2016-07-13 at 2.34.06 PM.png

                                     

                                    The screen pattern, halftone or stochastic, wouldn't come into play unless you applied a tint to your line. So a .25pt line with a 50% halftone screen applied is going to look something like this under a loupe:

                                     

                                    Screen Shot 2016-07-13 at 2.42.03 PM.png

                                    • 15. Re: Printing PS Points VS mm
                                      rob day Adobe Community Professional & MVP

                                      My guess is Adobe uses picas and points because it allows common translation into inch/metric forms, even if it doesn't report in whole units.

                                      InDesign's preferences let you customize a point's dimensions—you can assign any dimension between 60 and 80 points per inch to a point—see my #10. The default is 1/72

                                      • 16. Re: Printing PS Points VS mm
                                        Randy Hagan Adobe Community Professional

                                        Can't argue that, but then that would be an un-common measurement.

                                         

                                        InDesign also lets you define custom measurement units, But those wouldn't be default measures either.

                                        • 17. Re: Printing PS Points VS mm
                                          rob day Adobe Community Professional & MVP

                                          un-common measurement

                                          Right, but It seems like the OPs original question was: does the measurement unit you prefer affect output accuracy?, and I don't see how it does. As others have noted the accuracy of a line width is only limited by the output device capability. If we assume the line tint is 100% of a single color, the screen pattern resolution—halftone (lines per inch) or stochastic—doesn't come into play.

                                          • 18. Re: Printing PS Points VS mm
                                            De Pascalis Level 1

                                            A postscript point is EXACTLY 1/72 inch.

                                            I typed circa because I got the impression from this site that a point isn't exactly 1/72 inch.

                                            "To be extremely precise, 1 point is equal to .013836 inch, so 72 points are actually .996264 inch. For practical purposes, this is rounded up."

                                            None of the Indesign options listed (72, 72.23, 72.27, 72.3) equals to the value mentioned on that site. 1/.013836 = 72.2752... a value which I'm unfamiliar with.

                                            • 19. Re: Printing PS Points VS mm
                                              Peter Spier Most Valuable Participant (Moderator)

                                              No idea where they came up with that. This is probably a better reference: Point (typography) - Wikipedia, the free encyclopedia

                                              • 20. Re: Printing PS Points VS mm
                                                rob day Adobe Community Professional & MVP

                                                I typed circa because I got the impression from this site that a point isn't exactly 1/72 inch.

                                                I think that's why InDesign lets the user define the number of points in an inch—I like tom8to you like tomahto—but in the end it still doesn't affect output accuracy.

                                                • 21. Re: Printing PS Points VS mm
                                                  rob day Adobe Community Professional & MVP

                                                  None of the Indesign options listed (72, 72.23, 72.27, 72.3) equals to the value mentioned on that site. 1/.013836 = 72.2752... a value which I'm unfamiliar with.

                                                   

                                                  You can enter your preferred value within a thousandth of an inch:

                                                   

                                                  Screen Shot 2016-07-13 at 6.28.37 PM.png

                                                  • 22. Re: Printing PS Points VS mm
                                                    Stephen_A_Marsh Adobe Community Professional

                                                    Further to Rob’s reply, if one is tinting rules and there are repeating rules or a grid pattern, it will depend where on the final devices “pixel grid” the rules fall, which can result in different dot patterns for different rules, making some look thicker or thinner than others. The mockup image below is a 50% tinted rule, converted to a 150lpi halftone at 1200ppi resolution.

                                                     

                                                    50pc-150lpi-1200ppi.png

                                                     

                                                    One needs to pay special attention to tinted rules!

                                                    • 23. Re: Printing PS Points VS mm
                                                      Danny Whitehead. Level 4

                                                      The short answer is no, absolutely not.