Control Values

To set up the Control Value Table and the Pre-Program, you will have to measure the typical values of your typeface, and fill the ‘Control Values’ sheet. TTH can also ‘Detect’ those for you.

  • Zones:  alignment zones for baseline, overshoots, ascenders, descenders, capitals height, etc.


Name each zone, assign it a starting position, a width (top zones go upward, bottom zones go downward), and possibly deltas. Deltas syntax is ‘value1@size1, value2@size2, etc.’, the value is an integer between -8 and 8 (in /8th of pixel).

Example of Bottom Zone:

baseline | 0 | 15 | 0@0

Example of Top Zone:

x-height | 500 | 15 | 8@9, -8@17


  • Stems: typical stems thickness in both horizontal (X) and vertical (Y) directions, and values for pixel jumps at ppEm sizes.

Similarly, name each stem, assign it a width, and the pixel jumps should be calculated automatically but may be adjusted manually.

Example of X Stem:

LC_X | 79 | 0 | 25 | 37 | 50 | 63 | 75


  • General: essentially pre-program settings.


Stem snap precision: it’s the CVT cut-in limit. This is a threshold that determines if the Stem distance in pixels (pixel jumps) or the actual distance  is used. If there is a difference of more than the ‘stem snap’ between the actual distance and the CVT Stem distance, the actual distance will be used. If the difference is less, the CVT Stem distance will be used. So, the higher the ‘Stem snap’ is, the stronger the CVT Stems are. Default value is 17.

Stop zone alignment above: above a certain size, you may want to keep the overshoots and not to align everything on zones.  Default value is 48.

– Do not execute instructions above: above a certain size, you may want  not to use the instructions and let the rasterizer do the rounding job freely. Default value is 48.

Deactivate stems for grayscale and subpixel: An option that applies stem CVT control only for Monochrome rendering. It is a mean of getting better continuity (no pixel jumps) when there is antialiasing.

  • <gasp>:  defines the preferred rasterization technique for various size ranges.


You may add ranges with the wanted rasterization technique:

Gray Antialias: Hints are not applied, use grayscale smoothing.

GridFit: Use hints.

– Symmetric GridFit: ClearType GridFitting.

Symmetric Smoothing: ClearType Antialiasing.