Which size for DCP subtitles?

A question about the "best" size of DCP subtitles piqued my curiosity. Since I have access to a sample of DCP folders from a distributor, it was easy to do some statistics and find out what others felt was the right size for subtitles.

Executive summary: the answer is 42, which seems perfectly appropriate since it also happens to be "the answer to life, the universe and everything". (If you didn't know, you may be interested to see that Google's calculator does, and gives you the correct answer when asked this essential question).

 

All the DCP's I had access to used the CineCanvas (or Interop) standard for subtitles, which is described in the "Subtitle Specification for DLP Cinema" published by Texas Instruments. The document doesn't give an "official" size recommendation for subtitles, but it does provide a default size if the file doesn't specify it. The default is 42.

It also explains what the number 42 is supposed to mean (in the context of subtitles, not in that other more profound meaning):

"Size is given in points. Fonts are rendered as if the screen height is 11 inches, so a 72pt font would be 1/11 screen height.
Default Size = 42"

And that also seems to be the preferred size for the 124 feature length movies in my sample:

Font Size	Number of DCPs
36	1
37	2
38	7
39	21
40	10
41	3
42	68
44	6
45	3
46	1
47	1
48	1
Total	124

 

That disk also had 40 trailers with subtitles. For these, the preferred font size seems to be smaller at 39:

Font Size	Number of DCPs
39	31
40	1
41	1
42	6
44	1
Total	40

 

Points and pixels

There are 72 points per inch, so the screen height is 11 * 72 = 792 points.
In 2K, the DCP sizes are:

• 2048 x 1080 pixels for full frame
• 1998 x 1080 pixels for 1.85
• 2048 x  858 pixels for Cinemascope (2.39)

(In 4K, the sizes would be 4096x2160, 3996x2160 and 4096x1716 pixels)
So in full or 1.85:

• 792 points = 1080 pixels
• 1 point = 1.3636... pixels
• 1 pixel = 0.7333... points
• 42 points = 57.3 pixels

In Belle-Nuit Subtitler, the subtitle size appears to be set in pixels, which it then converts to points when exporting to "DLP Cinema".
I'm not sure about Cinemascope. Would 42 points be rendered as 45.5 pixels (42x858/792) ? Or still as 57 pixels ? Or would it depend on the projector ?