Chartotype

Char To Type
Convert and extend bitmap font dumps into a series of SVG files that are loaded into FontForge and exported as a font file.
Chartotype was made to be used with pixel fonts generated by classic 8-bit and 16-bit computers. It began as a little modification to Andy Teijelo's excellent Making an MSX font and become... something else.
Chartotype also makes it easy to extend the original (usually limited) character set. Just draw or modify characters on the bitmap dump, pairing them to their corresponding unicode character on the text file.

Go read Teijelo's blog, by the way. If you are here you probably like the subject and his explanation of the process behind the code is excellent.

Chartotype was only tested on a Mac but should (could? would?) work on a Windows or Linux PC? Maybe? Tell me.

Also take a look at Vectotype for an Illustrator template and a standalone scripts to convert SVG files into fonts.

How to use

Running

Chartotype works by reading a bitmap font dump .png and matching it with a .txt file with unicode characters on the same order as the ones on the bitmap, left to right, top to bottom. It will save enlarged B&W .bmp versions of the bitmap character and convert each of them to .svg. Then, it generates another script to be read inside FontForge that will load the .svg and create the font file.

To run the program, open Terminal and go to the Chartotype folder. There, run the Chartotype-A.py program with the font or system name as argument.

Chartotype-A.py <sys_name> [0|1|2|3]

After the system name there can be a multipurpose argument in the form of a single digit from 0 to 3
0 run the program without feedback
1 writes a dot for each converted character (default)
2 returns complete information on every character converted
3 (not implemented yet generate only Chartotype-B.py without processing the bitmaps and SVGs)

What is needed

Chartotype was developed on Python 2.7 and needs:

• potrace (the potrace executable must be on the Chartotype folder)
• The Pillow Python library
• FontForge

Inside the Chartotype folder there must be sub folders with the name (no spaces) of the intended systems or fonts to be converted. This will be called sys from now on.

Inside the sys folder there must be:

A bitmap font dump .png with the characters on a regular grid, cropped to the exact bounding size called sysCharMap.png

A unicode encoded text file following the bitmap character sequence called sysCharMap.txt

 !"#$%&'()*+,-./0123456789:;<=>?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[\]^_↑abcdefghijklmnopqrstuvwxyz{|}~←█▛▜▀▙▌▚▘▟▞▐▝▄▖▗▒

Also in this folder there must be a file called sysChartotype.ini (copy one of the examples) with the following content:

[BITMAP] Section with information about the bitmap cropping and .bmp and .svg saving settings.
char_width = NUMBER The characters horizontal size in pixels.
char_height = NUMBER The characters vertical size in pixels.
trim_width = NUMBER An horizontal crop factor (in pixels, from the right) for the character (ie. on MSX screen 0 mode the characters are 6x8 versions cropped from the 8x8 originals. The same 8x8 characters bitmap can be used to generate both sets)
trim_height = NUMBER Same as above but vertical (from the bottom)
resize_factor = NUMBER A factor to scale the bitmap for better vector interpretation. 8 works well.
invert_luma = BOOLEAN Chartotype tries to distinguish between the foreground and background color to generate a back and white .bmp with the font in black even on systems where the font is lighter than the background. However, If the colors are still inverted change this to True otherwise use False

[FONT] Section with configuration for the export font file .
glyph_width = NUMBER The width of the exported font characters (the font will be monospaced).
ascent = NUMBER The capital letter height of the output font. (To help the calculation this number can be on the format NUMBER - NUMBER, the first number being the full font height and the second being the descent)
descent = NUMBER The portion below the font baseline (the lower part of the lowercase "g" for instance)

It is recommended the height to be a power of 2 for TrueType fonts, usually 1024.
So it is common to have the ascent = 1024 - 128, descent = 128 and glyph_width = 1024 with width and descent varying according to the font proportions.

fontname = STRING the font name (no spaces).
fullname = STRING the font full name.
familyname = STRING the font family name.

[OPTIONAL] Optional configurations for the exported font.
os2_ascent = NUMBER An alternate ascent value.
os2_descent = NUMBER An alternate descent value.
os2_linegap = NUMBER A line gap value.

These values can be left blank.
They are useful if you want to add vertical (line) spacing to the font without changing its geometry. Usually, increasing the descent number is enough.

On the Chartotype folder there is a Chartotype.ini file with general program settings with content as follows:

[CHARTOTYPE]
auto_save = BOOLEAN If True automatically saves the FontForge project and the .ttf font file on the sys folder.
save_report = BOOLEAN If True saves a CSV .txt report with information about all the characters converted.
save_raw_png = BOOLEAN Chartotype uses enlarged B&W .bmp files to do the conversion. If this is True it will also save the separated original bitmapped characters on .png files.
delete_folders = BOOLEAN If True will delete all the working folders (except the PNGs) after the conversion.

After Chartotype-A.py is done, if told to, a sysReport.txt will be generated on the sys folder with information about all the characters found and the BMPs folder will be deleted.
Also another script will be generated/modified, Chartotype-B.py, with all that is needed to make the font file.

Chartotype-B

Chartotype-B.py must be called from inside FontForge on the File > Script Menu menu (pasting the script straight to the Execute Script... box doesn't always work). Configure the Script Menu on File > Preferences... > Script Menu this only needs to be done once as long as the path to Chartotype-B.py doesn't change.

Once set up, calling Chartotype-B.py inside FontForge will load each .sgv, assign them to their character slot, perform some optimisations and, if told to, save the project, export the font and delete the SVGs folder.

At this time you may want to revise the font on FontForge to see if all went according to plan and maybe do some manual adjustments.

This is often not needed but the initial Chartotype-A font settings can take some trial and error to get right.

I specially had problems with an horizontal proportioned font (A2600 Blocky, one of the examples) and had to adjust it manually on FontForge (configuring as square (ascent+descent=width), selected all the glyphs and changed size and scale on the Elements > Transformations > Transform... menu, checking Transform Width Too)

Acknowledgements

Enjoy and send feedback.
Thanks.

Chartotype is offered as is, with no guaranties whatsoever. I think it will behave however (mostly).