🚀 go-pugleaf

ab@nova.cc.purdue.edu (Allen B) writes:
>mmwang@adobe.com (Michael Wang) writes:
>> As the point size gets smaller than this optimum size, reading
>> comprehension begins to suffer  ...  Conversely, as the point size
>> gets larger, reading speed suffers ...
...
>...I'm just wondering how the optimum size is related to size
>(or, I guess it would be better to say "extent") and
>resolution.
...
>Let's not worry about resolution for the moment.  We can
>avoid that by assuming we're talking about billboards or
>very high resolution printer output.  The extent of a
>character on a billboard might be the same as that on a page
>at the expected viewing distance for both...

Yes, but there's one more factor which influences optimum size:  There's an
optimum viewing distance for the eye.  That is, the eye works best at one
particular distance.  If you look at 10 pt type from 1 foot distance, or
1000 pt type from 100 ft, the type has about the same apparent size (sub-
tends the same angle of view) to the eye...but the two aren't equally
readable.  For "normal" eyes, the close-in type is more easily read.

You can experiment with the eye's ability to resolve fine detail at various
distances.  In effect, you create a test chart of a certain size and use it
to test at one particular distance.  Then, say you double the size of the
test; use it to test at twice the distance.  Increase the size again and
increase the viewing distance by the same factor, test again.  What these
experiments find is that the eye's performance has a noticeable peak in
resolving power; resolution drops off at distances smaller or larger.  For
a normal eye (for some definition of "normal":-), the optimum distance is
supposed to be on the order of 25 cm or a little more.  (Make your rule of
thumb 25 cm if you use metric, a foot if you use English system.:-)  This
pins down one more constraint in choosing the best range of type size--
you know that it's not going to make sense to print in thumbnail format in
3-pt type for a book to be held just beyond the nose, nor at 18-pt in a
large format held at arm's length.  (This also gives one reason why "large
format" books for people with slight visual impairment won't become the
norm--they're not only more cumbersome; they're not as comfortably readable
to the average eye.)

>In Type 1 fonts, all the hinting is aimed at resolution
>limits and it seems to work OK.  What type of hinting
>mechanism would help optical scaling?  It'd be based on
>actual size (or extent if we know it), right?

It would be better to specify the desired effective (optical) size
explicitly.  That way (a) you don't get in trouble with re-scaling the
output by photo-reduction or the like, and (b) you don't have as much
bum code in applications grubbing around in the CTM.
-- 
Dick Dunn    rcd@raven.eklektix.com   -or-   raven!rcd    Boulder, Colorado
	...Simpler is better.