Let's start with the capital letters.
Bearing for Roman is relatively simple, or at least in theory it is based on clear principles.
The LSB and RSB in /O/ are the same; the LSB for /D/, /E/, /F/, /H/, /I/ etc are the same, and so on.
In Italic, on the other hand, I see completely different settings in various fonts. In GaramondPremierPro the measurements are completely different even for the same rods; in the Palatine the LSB is the same for /H/ and /I/, but completely different between /E/ and /F/, which nevertheless have the same design.
What then is the logic, the general conceptual approach of bearing, precisely for italic?
Thank you!
Comments
(a) the Italic needs to work alongside the roman (which can usually not be delivered without some kind of compromise – try typesetting “(f)” – you will need manual kerning),
(b) font editors may not offer complete tooling to aid italic spacing (I saw there was some functionality for this in FontLab but I found it a headache, so I opted out). Because of the angle, if you don't use such features to calculate the sidebearings at an angle, some distances may seem non-obvious, and the whole process is more prone to errors.
In fact, for example, the Minion Pro Italic has marked regularity.
In GaramondPremierPro Italic instead, to give an example, the LSB of /I/ is -20pt, that of /E/ which has the same profile -42 and that of /F/ -28. I wonder the reason for these deviations.
The LSB of Garamond Premiere himself is negative for almost all glyphs; in the Palatino it is positive for almost all glyphs. So I ask: what do we start from?
It seems to me that you consider it a more correct practice
Standardization may seem like a good idea, but I have to wonder whether this “cut and paste” ethos hasn’t been excessively promulgated by the hinting requirements established in the early days of digital, with low-res rendering.
I understand that the practice is to measure the bearing more or less in the middle of the stem. It also seems to me that for some it is good to "center" /H/, while the centering of /O/, very common practice for Roman, is not followed by many.
But, what then are the basic criteria for Italic, since in some fonts the location of the glyphs is very "shifted" to the left with a large amount of negative offset, while in others the location of the glyphs (obviously this will not be the case for the italic /f/) is much more centered in general?
Firstly, by examining how others have done it, by opening up their fonts and seeing if there are any general principles that emerge.
Secondly, by prototyping of your fonts in a variety of documents. A useful method here is to designate a benchmark font(s) that is well established, and see how your design performs in a rendering comparison of the same text and layout.
For instance, when I was developing the Pratt fonts for a Globe and Mail newspaper redesign, they were using Utopia; therefore, my design had to have at least the same character count and apparent size as that, &c., &c.
The bearing difference then strongly depends on the font style. The MinionPro has consistent lines and graces, and consequently the bearing as well.
The GaramondPremierPro is irregular, somewhat following the idea of calligraphy and nib markings, and features entirely different designs and sizes.
Even the width of the stems in some fonts is absolutely identical, in some others it has a certain variety.
In any case, your advice is worth studying the best fonts ...