3 Replies Latest reply on Sep 11, 2014 1:33 AM by [Jongware]

    How is first baseline offset ascent calculated?

    nrknthuk

      I'm trying to render some output from an Indesign plugin in another piece of software.

       

      On the left is some text in Avenir with the metrics (as extracted from the font file) drawn over the top. On the right is an Indesign text box with first baseline offset set to ascent.

       

      metrics.jpg

       

      There doesn't seem to be any direct correlation between the font metrics and the vertical offset used by Indesign when first baseline offset is set to ascent.

       

      The only correlation I can see is that text offset seems to match the difference between the em height and the ascender height?

       

      Can anyone confirm if this is in fact the correct offset? Or offer an alternative explanation?

        • 1. Re: How is first baseline offset ascent calculated?
          nrknthuk Level 1

          OK - just did some more testing. It's just a coincidence that the offset is the difference between the em size and ascender size when using Avenir. Doesn't hold true with, for example, Verdana.

          • 2. Re: How is first baseline offset ascent calculated?
            Eugene Tyson Adobe Community Professional & MVP

            From the InDesign Help Files

             

            First baseline offset options

            To change the first baseline options of a selected text frame, choose Object > Text Frame Options, and click the Baseline Options tab. The following options appear in the Offset menu under First Baseline:


            Ascent

            The height of the “d” character in the font falls below the top inset of the text frame.

             

            Cap Height

            The top of uppercase letters touch the top inset of the text frame.

             

            Leading

            Use the text’s leading value as the distance between the baseline of the first line of text and the top inset of the frame.

             

            X Height

            The height of the “x” character in the font falls below the top inset of the frame.

             

            Fixed

            Specify the distance between the baseline of the first line of text and the top inset of the frame.

             

            Min

            Select a minimum value for the baseline offset. For example, if Leading is selected and you specify a minimum value of 1p, InDesign uses the leading value only when it’s greater than 1 pica.

            • 3. Re: How is first baseline offset ascent calculated?
              [Jongware] Most Valuable Participant

              Take care to distinguish Ascents and Capitals. Both values are saved in the font file (also possible that InDesign does not count on designers getting that right, and simply measures the characters), and InDesign does use the correct value for each:

               

              baseline.PNG

               

              Top: Aligned top with Ascents. 'bdk' aligns perfectly, capitals do not. But Capital Height does not need to equal Ascender Height (although in regular fonts they are very close). In Verdana, your other test font, the difference is there as well but it is much smaller.

               

              Bottom: Aligned top with Capitals. Perfectly aligned.