Conversion of MS Word pt values into PPM values for FontLab

-Rudy-'s picture

I havent found anything about this. I hope I can explain it a bit...

For example: I have the character "Q" in MS Word at a size of 16 pt, this size is actualy 21 PPM in FontLab.
I also have the character "€" at a size of 10 in MS Word and which is actualy 13 PPM in FontLab.

Now my question is, does somebody have a list of all these conversions or a formula by which I can convert MS Word pt values into PPM values for FontLab?

Thanks in advance!

vinceconnare's picture

The general conversion is

point size * resolution (your OS rasterizer screen resolution) / 72 = PPEM

so this would mean your screen rasterizer is at 96 pixel per inch DPI.

16pt*96/72 = 21.33 or 21 PPEM

12pt*96/72= 16ppem etc.

-Rudy-'s picture

Just what I've been looking for, thanks Vince!

Rudy

twardoch's picture

Rudy,

the formula that Vincent has given above is in the FontLab Studio 5 user's manual in the first section ("Font Scaling, PPM") of chapter 9 ("Hinting"). I do recommend reading the FontLab Studio manual since it really includes some useful information about font development :)

Please note that 96 is not always the default DPI size on Windows. Some notebook manufacturers pre-install Windows with the "Large fonts" (120 DPI) setting, and of course some users have the choice to set a yet different Custom DPI. I used to work on a 133 DPI setting for quite some time on my Dell notebook (which had a 1600×1200 15 inch screen so the pixels really had a physical resolution of 133 DPI, and the default 96 DPI setting rendered type so small that it was unreadable).

Cheers,
Adam

-Rudy-'s picture

I actualy did read about Font Scaling, PPM in the FontLab manual a few weeks before I posted, only at that time I was searching for other info. By the time I needed this info, I didn't remember where I've read it and what it was called :P

I never change the DPI size of 96, I've gotten to used to it. The manufacturers pre-install always been 96 DPI with me so far.

Btw the manual does have a good explanation about the DPI conversion, thanks for the help Adam :)

Rudy

Rob O. Font's picture

>I actualy did read about Font Scaling...

Me too! I use this formula a lot, so res/72 * pts = ppm, is the choice of professionals as the easiest input to a calculator.

A higher dpi device generally means a given ppm appears smaller. And, at a higher dpi, a given point size requires more ppm to remain the same size.

So... indicating as that Vista dialog box does, that higher "DPI scaling" yields bigger type must be a windows way of saying 'OS zoom factor', cause though dpi does change from device to device, it does not scale.

Cheers!

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