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DTL LetterModeller 10.4 – ReadMe
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Last update: September 28, 2026

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License:

Please read the enclosed DTL Font Tools EULA carefully. Only proceed if you fully agree with the terms.

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Introduction:

DTL LetterModeller (LeMo) is developed by Frank E. Blokland, Jürgen Willrodt, Hartmut Schwarz, and
Axel Stoltenberg with a view to the exploration and parameterization of (certain parts of) type design processes.
The application is the result of the doctoral research of Blokland at Leiden University into the (effects of)
systemization, standardization, and unitization in Renaissance font production (https://www.lettermodel.org).

The ideas behind the application are based on Blokland’s educational program and typographic expertise as
Senior Lecturer at the Royal Academy of Art in The Hague (since 1987), and as associate professor and researcher
at the Plantin’s Institute of Typography in Antwerp (since 1995). The models can be used as direct basis for type
design, or in addition to writing with the broad nib and the pointed pen and subsequent letter drawing (and vice versa).

The type design process with LeMo is shown in this video: https://www.youtube.com/watch?v=IORbqkDZdoY

The current version of LeMo can be used to explore the harmonic, rhythmic, and related convention aspects of type
using a range of parameters (see also: https://www.lettermodel.org/indexd7ab.html). The generated glyphs can be
edited using the internal glyph editor and the results can be exported in the BE (Bezier), IK (IKARUS) and
UFO formats and as CFF- and TrueType-flavored OpenType fonts.

The current version of LeMo is capable of generating CFF and TrueType-ﬂavored OpenType fonts.
For hinting CFF and TTF the AFDKO and ttfautohint can be invoked respectively.

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Installing:

On macOS, extract the LeMo download (.zip) and place the resulting folder somewhere on your system,
for example in the Applications folder. If desired, create a shortcut to your desktop or Dock.
The app is code-signed and should start without any issues.

On Windows extract the LeMo download (.zip) and place the resulting folder somewhere on your system,
for example in the Program Files folder. Keep all the contents of the folder, including the DLL files, together.
Double-click on the LeMo.exe file to run LeMo. If desired, create a shortcut to your desktop.

On Linux, extract the LeMo download (.zip) and place the resulting folder anywhere on your system.
LeMo 10.4 may require installation of ICU 60 libraries, because recent Linux distributions often include
newer versions of ICU. For guidance, the download includes an ICU60 Installation Manual (PDF).

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Minimal requirements:
For macOS:
- Intel version: Mac running macOS 10.14.6 (Mojave) or newer.
– ARM version: Apple Silicon (m1, M2, etc.). Note that the Intel version also runs under Rosetta 2.
- Hard-disk space: about 30–40 MB, depending on the version.
- Memory: 1 GB or more should be sufficient.

For Windows:
– Any 64-bit system from Windows 7.
- Hard-disk space: about 40 MB.
- Memory: 1 GB or more should be sufficient.

For Linux:

– On main distributions, LeMo 10.4 may require installation of ICU 60 libraries, because recent Linux
distributions often include newer versions of ICU.some other Linux distributions may require one or more additional dependencies.
- Hard-disk space: about 70 MB.
- Memory: 1 GB or more should be sufficient.

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New in version 10.2–10.4:

– Apple-Silicon native build.
– Fully code-signed for macOS.

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New in version 7.0:

–Export of OpenType TTF.
–Bug when exporting OpenType in Windows 64-bit version removed.

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New in version 6.9:

–32 and 64 bit versions for Windows.

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Version 6.8 was only used internally at DTL for development purposes.

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New in version 6.7:

–Button for default skeleton font ﬁle added.
–Last visited location for selecting skeleton ﬁle is stored.
–Find and replace function added to tool box.

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New in version 6.6:

–Skeleton font ﬁles can be selected from pull-down menu now.

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Versions 6.4 and 6.5 were only used internally at DTL for development purposes.

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New in version 6.3:

–A range of shortcuts for the drawing functions under the ‘Shift’, i.e., pointer tool.
–Optional ‘calligraphic’ skeleton added.

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Versions 5.9 – 6.2 were only used internally at DTL for development purposes.

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New in version 5.8:

The tools icons can be selected one by one or all together. Hence the icons pallet can be adapted to one’s needs. Furthermore 
the  ‘Quick Mode’ tool’s functions have been integrated in the ‘Shift’ (pointer) tool. This makes a three-button mouse not 
necessary anymore.

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Versions 5.1 – 5.7 were only used internally at DTL for development purposes.

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New in version 5.0:

This version of LeMo has become a full-functioning glyph editor. In previous versions of LeMo the glyph editor was restricted 
to the newly generated glyph database; as soon as this database was closed it was not possible to open it again in LeMo. The 
latter is now supported by LeMo 5. Furthermore, a couple of functions make the design and font-generation process much easier. 
For instance the calculation of the bodysize is now based on values at hand from the user interface. This means that the 
em-square is calculated from the distance from the top of the lowercase l to the bottom of the lowercase p. Ascender, descender, 
and x-height from the will appear as cap-height, x-height, and base line distance in the font header. If parameters are altered 
in the main LeMo interface, automatically the em-square will be scaled accordingly. Of course, the calculated values can be 
overwritten manually in the font-header editor. Another improvement is that for the export of OpenType fonts or .ufo ﬁles, 
a hard-coded default .cha ﬁle is used (which can be overwritten by the end user).

- Enhanced glyph editor.
- Import and export of the .ufo format.
- Editing option for font-header values.
- Dialog for 'presets' ﬁles.
- Dialog for preferences.
-Technically improved interface.

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Versions 3.2 – 4.9 were only used internally at DTL for development purposes.

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New in version 3.1:

- Full-functioning glyph editor.
- The option to export CFF- and TrueType-flavored OpenType fonts.

The current version of LeMo is capable of generating CFF- and TrueType-flavored OpenType fonts. However, hinting is not built-in 
yet. For this purpose it is recommended to use the auto-hinter in the AFDKO 
(https://github.com/adobe-type-tools/afdko/blob/master/FDK/Read_Me_First.html) for .otf fonts and ttfautohint 
(http://www.freetype.org/ttfautohint/) for TrueType fonts.

LeMo contains also a full-functioning glyph editor now, which is almost identical to one built in DTL FoundryMaster. Please note 
that editing of glyphs in LeMo is only possible on a newly-generated BE- or IK-database. As soon as leMo is quit, there is no 
option to open the file again. For fur editing either FoundryMaster or the DTL FontMaster editors are required. Currently LeMo 
also does not support the generation of OpenType Layout features features. For this purpose DTL OTMaster can be used, because 
this contains the famous features-subsetting functionality that also can be found in DTL FontMaster.

Please note that for letterforms outside the primary harmonic and secondary harmonic models, such as the 'spectacle' g, s and ]
capitals, a skeleton font (IK format) with the hard coded name 'skeleton.ik' can be added.
For the Windows and Linux versions this file should be placed in the current working directory, i.e. where the program executable 
resides. On the Mac, the file 'skeleton.ik' is expected to reside in one of the application's subdirectories, namely in 
.../phm.app/Contents/MacOS/.

The parameters will be applied on the glyphs in the skeleton font too. The skeleton font can contain all characters in the ASCII 
range. In case of an overlap with the characters that are constructed using the harmonic models, the characters in the skeleton 
font will supersede the ones in the models. The height of the capitals is connected to the ascender height.
Because the construction of the serifs is related to that of the primary harmonic model, serifs cannot be added to the skeleton 
font using the applicable radio buttons.

The manual is also under development still and is far from complete. It covers most of the editing functions, but for the 
generation of fonts the older DataMaster (part of the FM-suite) manual has been included. Although the file structure used by 
FoundryMaster is identical of that in FontMaster, the interfaces of FoundryMaster and DataMaster are not fully identical. 
Overall the information supplied by the DM manual should be sufficient though.

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New in version 3.0.1:

- The RSB/LSB values of (A-Z, 0-9,... [any other character within the ASCII range]) are now derived from the 'skeleton.ik' font. 
Pen width and angle have an influence on the metrics as well.
- The contouring algorithm for the pen-height-effect on a...z now uses different parameters in order to avoid long peaks, which 
might destroy characters under certain circumstances.
- The handling of LSB/RSB has been improved for a...z when an italic angle is applied.
- A graphical character overview to select a character when the editor is opened has been added.

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New in version 3.0:

- 'Pen thickness' parameter is supported now.
- 'Auto spacing' based on the rhythmic system is automatically applied on the letters from the primary harmonic model. The 
secondary harmonic model is treated differently: the right side of the k and the left and rights sides of the v-z range are just 
spaced 'tightly' (50 IK-units).
- An outline editor, which makes glyph editing possible after exporting the font data, has been added.
- Export of EPS and SVG formats from the glyph editor.
- The character 'x' is now constructed differently in order to avoid a self-overlapping contour, which could lead to missing 
character parts.
- For letterforms outside the primary harmonic and secondary harmonic models, such as the 'spectacle' g, s and capitals, a 
skeleton font (IK format) with the hard coded name 'skeleton.ik' can be added.
For the Windows and Linux versions this file should be placed in the current working directory, i.e. where the program executable 
resides. On the Mac, the file 'skeleton.ik' is expected to reside in one of the application's subdirectories, namely in 
.../phm.app/Contents/MacOS/.
The parameters will be applied on the glyphs in the skeleton font too. The skeleton font can contain all characters in the 
ASCII range. In case of an overlap with the characters that are constructed using the harmonic models, the characters in the 
skeleton font will supersede the ones in the models. The height of the capitals is connected to the ascender height.
Because the construction of the serifs is related to that of the primary harmonic model, serifs cannot be added to the skeleton 
font using the applicable radio buttons.

Skeleton fonts can be constructed with DTL IkarusMaster (light).
The hard coded mapping of URW numbers to ASCII for the 'skeleton.ik' fonts is as follows:


URW #; ASCII #; character;

101;  ASCII 65;  A;
102;  ASCII 66;  B;
103;  ASCII 67;  C;
104;  ASCII 68;  D;
105;  ASCII 69;  E;
106;  ASCII 70;  F;
107;  ASCII 71;  G;
108;  ASCII 72;  H;
109;  ASCII 73;  I;
110;  ASCII 74;  J;
111;  ASCII 75;  K;
112;  ASCII 76;  L;
113;  ASCII 77;  M;
114;  ASCII 78;  N;
115;  ASCII 79;  O;
116;  ASCII 80;  P;
117;  ASCII 81;  Q;
118;  ASCII 82;  R;
119;  ASCII 83;  S;
120;  ASCII 84;  T;
121;  ASCII 85;  U;
122;  ASCII 86;  V;
123;  ASCII 87;  W;
124;  ASCII 88;  X;
125;  ASCII 89;  Y;
126;  ASCII 90;  Z;

301;  ASCII 97;  a;
302;  ASCII 98;  b;
303;  ASCII 99;  c;
304;  ASCII 100; d;
305;  ASCII 101; e;
306;  ASCII 102; f;
307;  ASCII 103; g;
308;  ASCII 104; h;
309;  ASCII 105; i;
310;  ASCII 106; j;
311;  ASCII 107; k;
312;  ASCII 108; l;
313;  ASCII 109; m;
314;  ASCII 110; n;
315;  ASCII 111; o;
316;  ASCII 112; p;
317;  ASCII 113; q;
318;  ASCII 114; r;
319;  ASCII 115; s;
320;  ASCII 116; t;
321;  ASCII 117; u;
322;  ASCII 118; v;
323;  ASCII 119; w;
324;  ASCII 120; x;
325;  ASCII 121; y;
326;  ASCII 122; z;

501;  ASCII 49; one;
502;  ASCII 50; two;
503;  ASCII 51; three;
504;  ASCII 52; four;
505;  ASCII 53; five;
506;  ASCII 54; six;
507;  ASCII 55; seven;
508;  ASCII 56; eight;
509;  ASCII 57; nine;
510;  ASCII 48; zero;

614;  ASCII 33; exclam;
636;  ASCII 34; quotedbl;
638;  ASCII 35; numbersign;
512;  ASCII 36; dollar;
698;  ASCII 37; percent;
630;  ASCII 38; ampersand;
635;  ASCII 39; quotesingle;
626;  ASCII 40; parenleft;
627;  ASCII 41; parenright;
634;  ASCII 42; asterisk;
640;  ASCII 43; plus;
607;  ASCII 44; comma;
623;  ASCII 45; hyphen;
601;  ASCII 46; period;
622;  ASCII 47; slash;
602;  ASCII 58; colon;
608;  ASCII 59; semicolon;
1111; ASCII 60; less;
644;  ASCII 61; equal;
1112; ASCII 62; greater;
616;  ASCII 63; question;
637;  ASCII 64; at;
628;  ASCII 91; bracketleft;
700;  ASCII 92; backslash;
629;  ASCII 93; bracketright;
1151; ASCII 94; asciicircum;
1154; ASCII 95; underscore;
755;  ASCII 96; grave;
655;  ASCII 123; braceleft;
1152; ASCII 124; bar;
656;  ASCII 125; braceright;
1337; ASCII 126; asciitilde;

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New in version 2.0:

- Optional serifs
- Predefined sets
- Bodysize entry
- Curve flattening
- Some other improvements, such as shift to baseline have been made and some bugs
that prevented the proper functioning of the 1.7.0 version on some systems have
been removed.

1. Optional serifs
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There is a new radio button 'Curved endings'/'Basic serifs' in the GUI to switch
between curved stroke endings and serifs. The serifs can be applied in combination
with all other parameter settings.

2. Predefined sets
-------------------------------
When the program starts, it now looks for a file named 'presets.txt'. For the
Windows and Linux versions this file should be placed in the current working
directory, i.e., where the program executable resides. On the Mac, the file
'presets.txt' is expected to reside in one of the application's subdirectories,
namely in .../phm.app/Contents/MacOS/. If the 'presets.txt' file is present and
it's syntax is correct, it will be used to fill the 'Predefined sets' combo box.
If not present, some arbitrary hard coded presets will be used.

The format of 'presets.txt' is a colon-delimited ascii-file. Every line must
contain 14 entries (so, no blank lines, no comments etc.) representing the
(sequence of the) following parameters:

preset_name; pen_width; pen_thickness; pen_angle; x_height; ascender; descender;
stretch_factor; curve_flattening; italic_angle; stretch_factor_exeptions;
pen_angle_exeptions; pen_angle_for_exeptions; chars_to_display;

Please note that leading and trailing blanks of all entries are simply ignored, so
...; 10.0;... will function identically as ...;10.0;...

(The idea is to develop a 'LetterMeasurer' tool that uses the primary Harmonic
Model (phm) to find the parameters behind digital roman type and which has a
'preset/txt' file as output.)

3. Bodysize entry
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This entry is used when storing/exporting the data in a font file. The default
setting is 15000 units. A number of the parameters, such as for x-height and
ascender/descender values have to be defined in millimetres. The relation between
the bodysize units and millimetres is here 1/100 mm = 1 unit.

For placing the glyphs 'tightly' in the em-square, the bodysize should be the sum
of ascender + x-height + descender in millimetres multiplied by 100. Any preferred
scaling (for instance to an em -square of 1000 units for the Bezier format), can
be done in the Bezier and Ikarus editors of DTL FontMaster (Light).

4. Curve flattening
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This can be used for obtaining a 'Textura-like' effect, i.e., to bridge the text letters from the Renaissance with the 
variants of the Middle Ages.

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Known issues

- The 'k' and the 'v-z' range are not working properly when serifs are attached.
Technically the 'k' is problematic, as with standard parameters, there is a self-
overlapping contour -so no 'hidden lines' algorithm is used after attaching the
serifs to the 'k'. The 'x' is also problematic sometimes, as one of its diagonal
stems disappears/reappears when moving the pen angle slider.
(Basically the range 'k,v,w,x,y,z' needs a different approach. The letters of the
'primary Harmonic Model' (phm) find their origin in the broad nib and the other
letters, which are derived from the capitals, in 'skeleton' lines. On the
'skeleton' letters one should apply the effects of the broad nib used for the phm
then. This will be implemented in the next LeMo version)

- The diagonal of the 'e' sometimes extends the curved part; it is not easy to
find a formula that gives the correct length of this stem as a function of all
possible parameters.

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Dutch Type Library
Zwaenenstede 49
5221 KC  's-Hertogenbosch
The Netherlands
phone: + 31 (0)73 614 95 36
fax: + 31 (0)73 613 98 23

info@dutchtypelibrary.com
https://www.fontmaster.nl
https://www.dtl.nl

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Copyright (c) Dutch Type Library, 2009-2026

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