Perception and scaling of inter-letter space

[nina]

This topic was imported from the Typophile platform

Here's something I've been thinking about and would love some input on. I'm sure this has been discussed at length before, and I know I'm still in a very early stage of learning, so I'll be equally glad about pointers to older threads, and/or literature.

Looking at Briem's page on spacing, I noticed he employs the "glass of water" analogy to describe correct spacing ("the same volume of water that filled the counters should also fill the gaps between the letters"), which is also how I was taught letterspacing at design school.
A different description, which —being more functionally-oriented than merely formalistically descriptive— intuitively seems to make more sense, is this one that I just came across in Peter Enneson's article in TYPO #13 (page 26): "Perceptual distances between letterforms must be great enough to minimize criterial cue confusions or masking. But not be so large that cross-letter binding or constructive conjunction is inhibited."

So here's the question. Especially compared to definions such as Peter Enneson's quoted above, I'm suspecting the "glass of water" model is overly simplistic – mainly because of the issue of optical scaling, the need of which I'm not sure it can accommodate. My impression from a typesetting/typography perspective is that the need for a relative expansion of inter-letter space (OK, tracking) is much increased at smaller point sizes. Now I know that optimally, setting text at a smaller size means employing a dedicated optically-sized cut, which (inter alia) increases the relative width and visible counterspace of the lettershapes. But it seems that the inter-letter space needs to be adjusted more for smaller sizes than the intra-letter space usually is – as in, the adjustments made to intra- and inter-letter space seem not to be linear.

If this is indeed so, then I'm wondering why. Does the effect of lateral interference increase at smaller sizes? Also, if intra- and inter-letter space do not in fact scale in a linear fashion, how can one talk about glasses of water without factoring in target point size?

Or am I mistaken (and most likely, visually misdirected from working too much with non-optically-sized digital fonts) and in proper optical sizing, the scaling of intra- and inter-letter space actually is parallel/linear, so that the concept of optical scaling does not in fact refute the "glass of water" model?

[daniele capo]

Well, consider the two shapes in the image below

 

they have the same area (‘volume of water’), do they 'look' equivalent? Even if you can calculate the volume of intra/interspaces, trying to equalize volumes (numerically) is a very crude approach, I suspect.
I don’t know much about perception but I think you need to consider other factors, like the 'compactness' of a shape, the absolute dimensions, etc.

daniele

[nina]

"I think you need to consider other factors, like the ’compactness’ of a shape, the absolute dimensions, etc."
Certainly. I sure hope the adherents of the "glass of water" model wouldn't apply the principle mechanically/mathematically (that would be scary), but adjust the space optically – but still based on the "glass of water" idea. (FWIW, that's what they taught me at school.)

Still, the metaphor is there and I wonder how much merit it has. How elastic can a glass be (esp regarding the point size question) before it stops being a glass? :->

As a PS, I just remembered a slightly different metaphor used by Jost Hochuli, who talks about the white as light shining into the lettershapes, which allows for slightly finer gradations (like he says light coming from above is stronger, which is why a sans serif "u" needs to be narrower than an "n") but still departs from the idea of equal "light" inside and around the letters.

[daniele capo]

Thanks for having quoted the light metaphor (I didn’t know about it), I like it. My hypothesis is that the liquid you have in the glass is not homogeneous and/or it can be 'activated'/'de/activated' by the boundaries of the glass.

[nina]

Cool, sci-fi plasma fluid! :-)

I can look up the light metaphor and quote it more precisely if you're interested.
But I read it in a book I don't have, so I'd hit the library tomorrow.

[dezcom]

Nina, Yes, generally, larger type needs less interletter spacing. Other things occur along with the visual mass concept (glass of water theory expanded to include perceptual bias). A big factor is proximity of nearest segment--meaning a serif on a cap V being near a Serif on a cap W. When the two are quite close, the proximity factor begins to overcome part of the visual mass of space issue. It is often impossible to have a space as those between upright adjacent letters like H and N be truly equal to adjacent opposing diagonals like V and Y unless you vastly letterspace. Using the proximity effect minimizes the perceived difference though.

ChrisL

[hrant]

That glass of water is not drinkable - dump it down the drain.
Proximity of parts is a central parameter.

hhp

[nina]

Thanks guys. Sounds like the "glass of water" model, at the very least, isn't accounting for everything that needs to be considered.

"Yes, generally, larger type needs less interletter spacing."
Thanks for confirming this, Chris.
I still wonder why, if anyone is up for explaining that. Maybe something to do with there being absolute limits to visibility of interletter space (especially related to the proximity parameter*)?

* Which I can see now is probably included in the concept of "perceptual distance" quoted above (I read "distance" as a linear concept rather than [only] volume-based).

[dezcom]

It could be like a visual Doppler effect where sound appears to increase in pitch as it gets closer,

ChrisL

[nina]

?
Sounds mysterious! (I know what the Doppler effect is, but I don't get how the translation works.)

[dezcom]

It is an effect of perception, not an actual effect on pitch of sound. Translated to looking at small type, our perception may make a feeling of closure to neighboring glyphs, at some point, almost a sense of gravitational pull takes effect but only in our eyes.

ChrisL

[nina]

No offense Chris, and I'm not contesting what you said, but this sounds a bit esoteric. :-)
And maybe this stuff is just that – but I guess I'm wondering if there are any attempts to find out how this funny effect of perception* comes about.

* By the way, I always thought the Doppler effect is an actual effect on pitch of sound, in the way that sound waves emanating from a moving object in the direction of that movement (relative to the observer) are "squooshed", making for a different received frequency – not just the brain playing tricks? I may be mistaken though.

[Chris Dean]

I post "tracking" when I want to follow a thread so it "bookmarks" it in my account settings. RSS seems to not work on my current computer. Funny miscommunication given the content of this thread eh? None taken.

[nina]

Christopher, I was talking to ChrisL. I only got confused about your "Tracking" posts the first twenty times or so I saw them. :->

[Chris Dean]

@ A,

That made me laugh. Thank you.

[dezcom]

Nina, the sound of a car engine at the source is a given pitch and does not change. Sound moving through an air mass with dense atmosphere can alter what hits your ear some distance away but does not truly change the source of the sound (the car engine). Granted, I am making a metaphoric comparison, not a scientific one--so far, none exists. The ratio of letterspace to glyph does not change in reality but it appears to. Since the eye is always the final arbiter, we have to appease then not a measuring device. There may come a day when science has a more measurable reason for the difference and can predict the proper distance of change but it is just easier to make your change visually. Take a font designed for text reading and another for display from the same family and scale them to the same size. You will see the difference but you may not find a ratio of change that suits all families of type.

ChrisL

[nina]

"the sound of a car engine at the source is a given pitch and does not change."
Of course not at the source, but in this case, in the space between the source and the ear; I'd put that in the realm of physics, not perceptional psychology. Whereas with the issue of spaces between small lettershapes, I wouldn't expect some light rays to physically go astray on the way to the eye – but rather something strange to happen inside the eye, or the brain? But that's conjecture, and maybe also semantics rather than anything else.

"Since the eye is always the final arbiter, we have to appease then not a measuring device."
Oh that point is totally clear. And I wasn't looking for numbers (how much to adjust it by, or something). I'm just very curious to learn how perception works, maybe overly so. If you say science doesn't know yet, that's an answer.

[dezcom]

Nina,

My sound analogy probably was less helpful than confusing :-)

We actually only anecdotally know that it works--even preferentially if you count legibility studies where "increased letter spacing" seems to be preferred by subjects of studies at reading text sizes. I don't remember the names of the studies any more and am sadly only left with what the perceived conclusion was. We are all curious to find out more about how perception works. There have been numerous studies but the why and how to part still does not seem clear enough to help a type designer much more than trial amd error. Oh, well, sorry I could not be of much help.

ChrisL

[1985]

I might have said this before but I always thought a surface area calculator would be a useful plug-in. Not to be relied on, of course.

[dberlowgone]

"And I wasn’t looking for numbers (how much to adjust it by, or something)"
Following, Briem’s page on spacing you always have the type you are employing to guide you. So, if you are composing type, and you want to see what tracking works, and how the glasses of water are equalized, set a line like iiiniii in the face you are spacing, or IIIHIII if caps, (the i's and l's have 'no water inside' and the n or H show you the how the average inside space relates). With tracking you can adjust this text sample so that the space between i's and the counter of the n are even, or as I and many others prefer, with slightly less space outside than in. Then, you can apply this tracking to broader text.

"I post “tracking” when I want to follow a thread so it “bookmarks” it in my account settings."
...but like so many things we are all free to do, if we all did this...

Cheers!

[kentlew]

> But it seems that the inter-letter space needs to be adjusted more for smaller sizes than the intra-letter space usually is

Nina, can you explain what you base this statement on? I'm just interested in understanding your frame of reference. I want to make sure I'm reading you right. You're saying that it seems that for smaller sizes the space inside letters is usually adjusted more than the space between letters. Did I get that right?

Are you thinking about a comparison of text to small text, or are you comparing display to text? (I think these are definitely two different paradigms, so I want to understand which you're talking about.)

And are you looking at/thinking about metal type (which was inherently optically scaled) or current "opticals" like what Adobe and others have done?

-- Kent.

[William Berkson]

The glass of water thing in Briem is seriously misleading if you take it too seriously. Looking visually equal and actually being equal in area are two different things. I've tested it by measuring inter-letter areas between nn and oo on well-spaced type. They're not mathematically equal, even though they look nicely balanced.

As well as visual equality of inter-letter space, making the outer space proportional to inner counter space, keeping adjacent parts from visually crowding, keeping a (not exact) regular rhythm of verticals and white, and even adjusting for weight of strokes--left vs right side of M--are all things to consider and weigh. And they are sometimes in conflict with one another.

I certainly don't claim to know the ideal way to balance all these. Then again there may not be any ideal, but various compromises.

Oh, and it does change with optical size. Further, the tightening of display vs text is probably best not simply tracking tighter. The oo and ll may work a little differently--at least that's Slimbach's view.

[Bendy]

With tiny letters, the whitespace is tiny too...so that the eye needs to be much more acute if the letterspacing isn't increased (due to clotting). So there's an inverse relationship, but I don't imagine that it's a linear one. And I imagine that the intra-letter space doesn't change so much because the letterforms themselves are still recognisable as long as they're not crunched up next to other ones? However, I think also that the x-height tends to increase as your point size goes down too?

I don't know enough, again! :)

[Bert Vanderveen]

Could it be that there is a very simple technical explanation/reason for larger sidings in small type vs smaller in larger type? Eg the fact that there is a lot more wear and tear on the parts of metal type that are close the the edge?

I imagine a natural process having taken place where the typecasters explored this and came to the evident conclusion that there is a minimum amount of sidebearing needed to keep type in good shape (at least for a period long enough…).

Readers would of course become accustomed to this and notice discrepancies from this practice, making it kind of obligatory to continue, even after we left metal type behind.

. . .
Bert Vanderveen BNO

[dezcom]

Nina,
Post away. You are not too demanding at all! Your posts are intelligent and insightful!

ChrisL