CAD to bitmap conversion
************************

The Smart Print software includes a conversion module for turning a
vector drawing (DXF, GDS, etc.) into the bitmap format required by the
projector.

These instructions describe an alternative tool chain that focuses on
producing sharp structures down to the the single pixel level.



For 10X objective:
==================


DraftSight
----------

Draw your pattern in DraftSight (or other CAD software).

Draw your polygons on a grid, i.e., use coordinates that are multiples
of either:
 
  (a) 2 um (or 2/3 um). With the conversion factor suggested below,
      this will translate to 3 pixels = 2.1 um on the real exposed
      image.

  (b) 0.7 um. This way you avoid the 5% inconsistency between your DXF
      and projected image, but it makes the coordinates messier to
      read and manipulate.

Save as DXF. (In DrafSight, specifically as "R2013 ASCII drawing".)


Inkscape
--------

Open the DXF to Inkscape. Use the "File -> Open..." menu, rather
than "File -> Import...".

  (a) Inkscape assumes mm units for the DXF, but I'll assume they are
      really um.

  (b) In the import menu, use the following conversion factor between
      DXF coordinates and mm in Inkscape, depending on the grid you
      chose for the DXF:

      If you designed on a 2 um grid:
      Conversion factor = 1/(2 mm/ 3 px * 90 dpi)
                        = 1/(0.7 mm/px * 90 / 25.4 px/mm)
                        = 0.423333333

      This gives slightly incorrect scaling (dimensions 5% bigger
      than in the DXF), but perfect pixel commensurability with
      designs made on a 2 um grid (in the DXF).

      If you instead want perfect dimensional accuracy, or made your
      drawing on a 0.7 um grid, use: Conversion factor = 1/(0.7 mm/px
      * 90 dpi) = 1/(0.7 mm/px * 90 / 25.4 px/mm) = 0.403174603

Under File -> Document properties...:

  (a) Set document width (height) to an odd integer multiple of 1920
      px (1080 px).

  (b) Set "Background color" to pure white (RGBA: ffffffff) instead of
      transparent.

  (c) Uncheck "Use antialiasing" (unless you want it).

Select everything in your design. Shift everything horizontally and
vertically by half the canvas size. Use the exact move command under
"Transform".

Select everything and set fill to solid black and stroke paint to
none.

Delete extra layers ("0" and "Defpoints" if DXF created using
DraftSight).

Set the visibility of your layers as desired.

Save as SVG.

You can now export a PNG from Inkscape

  (a) Export area: "page"

  (b) 90 DPI

Check the exported bitmap. Note that some PNG viewers apply an
antialiasing filter of their own when viewing the file (e.g. Document
Viewer in Ubuntu 16.04). If in doubt, check by opening the exported
PNG in Gimp.

The resulting file should have sharp edges for vertical and horizontal
lines (drawn on grid). Angled edges have grayscale colors, which you
can saturate to black (or white) in Gimp if you wish.

You can also import the SVG directly into Gimp if the PNG export from
Inkscape has issues.


Gimp
----

If importing the SVG to Gimp:

 (a) Use 90 DPI.

 (b) Right click on image -> Layer -> Transparency -> Remove alpha
     channel.

To turn all gray pixels into black/white, use Colors -> Threshold...

Export to PNG (or BMP).



For 2.5X objective
==================

Same steps, except:

  (a) Design your drawing on a 3 um grid in the DXF (or 2.8 um).

  (b) Import to Inkscape using the following conversion factor:
 
     For slightly incorrect scaling, but perfect commensurability with
     design on a 3 um grid: 1/(3 mm/px * 90 dpi) = 1/(3 mm/px * 90 /
     25.4 px/mm) = 0.094074074

     For perfect dimensional accuracy (or 2.8 um grid in DXF):
     1/(2.8 mm/px * 90 dpi) = 1/(2.8 mm/px * 90 / 25.4 px/mm)
     = 0.100793651