gdmodule true type font size

[John Hunter]

When using gdmodule to draw text using true type fonts

im.string_ttf(font, fontsize, angle, (x,y), s, color)

the docs say 'draw string s at (x,y) using the TrueType font at the
given pointsize and angle.' It is not clear to me how gd handles
point size. A fontsize of 12 should be 12/72 = 1/6 inches tall but
how does gd decide what an inch is? 72 pixels? Is there some scale
parameter or constant that allows gd to make the conversion from
pixels to points?

I want my text to scale with image resolution which is determined by a
dpi parameter, and I tried doing

scale = dpi/72.0
im.string_ttf(font, scale*fontsize, angle, (x,y), s, color)

but the fonts are larger than they should be, at least according to my
calculations.

Thanks,
John Hunter