Draft for “4.2 Justification”
Of the four basic justification methods (flush left, flush right, justified, and centered), justified is the most challenging, as it requires changing the widths of the lines to a pre-defined measure. “Measure” refers to the width of a column of text. In a justified paragraph the width of all the lines should be the same as the paragraph’s measure (except, of course, the list line).
In Arabic there are six mechanisms for changing the width of a line of text. Each one has its limitations and considerations on when and how it can be applied. Furthermore, different typographers and calligraphers have divergent preferences for these mechanisms.
An important factor in the application of these mechanisms is they success in creating an even “color”. The color of the text refers to the amount of ink/blackness used to print or show a block of text. Color describes the density of the text against its background. Poorly justifying paragraphs can create uneven distribution of color.
These mechanisms are not exclusive. Quite the contrary, they are commonly used simultaneously to produce better justified paragraphs. Combination of these mechanisms is discussed in Combination of the Mechanisms.
This is the same mechanism widely used when justifying Latin scripts, where the width of the spaces between the words can be increased or decreased to change the width of the line.
Figure 1: Aligning lines by increasing and decreasing spaces between the words.
A minimum width is defined for how much the space can be shrunk, because putting the words too close to each other creates aesthetic and legibility problems.
Stretching the space too wide is also undesirable, but is utilized as a last resort when it is not possible to use other solutions to make fully justified paragraphs. In some applications a maximum width for the inter-word space is defined as a soft limit (compared to minimum width which is a hard limit). Reaching the maximum width makes the software to try to use other solutions for justification. If no other solution could yield the required result, the software would fall back to inter-word spacing and stretch the space past the maximum width.
Depending solely on this mechanism for aligning lines in a justified paragraph can lead to unpleasant results, such as rivers (multiple stretched spaces appearing vertically close to each other and forming a white gap inside the paragraph) and uneven distribution of color in the paragraph. Hence, typographers generally use other mechanisms as well to minimize the effect of adjusting inter-word spaces.
This solution alters the space between letters of each word to change the width of the text. Like adjusting inter-word spaces, this is used for Latin scripts as well, but using it for Arabic script involves considerations specific to Arabic, as noted in Joining and Intra-Word Spaces.
+(ri: i suggest adding something like the following: The principal consideration is that gaps between characters only exist for those letters that join only to the right, such as .... Adjustment of intra-word space is not relevant where one letter is joined to its neighbour.) +
Figure 2: Altering intra-word spaces between unjoined letters.
Depending on the writing style and the typeface in use, different amounts of alteration to the intra-word space is acceptable for Arabic. Some writing styles allow more liberal adjustments to the closeness of the letter groups, while others can only accept small adjustments in this regard.
+(ri: I think that intra-word spacing is much less common and involves much smaller adjustments than what we are talking about when we look at inter-word spacing. It may be worthwhile to mention that(?)) +
In addition to the four joining forms (isolated, initial, medial, and final), each Arabic letter can come with different shapes while preserving its joining form. For instance, a typeface or writing style can offer two or more shapes for the final form of a single letter.
These variant shapes usually have variant widths and hence can be used to adjust the width of the line.
Figure 3: Alternative shapes for changing the width of the text.
An advantage of using alternative letter shapes when justifying paragraphs is that it does not involve modifying default properties of the typeface (width of space or other characters). Instead, it is using shapes that are part of the typeface and are in harmony with other shapes in the lines.
But excessive use of alternative shapes, such as using multiple very wide alternatives close to each other, can create unnatural results.
It is not possible to justify paragraphs using only alternative letter shapes, because these shapes have predefined widths. For example, if a line should get 25 points wider, it is impossible to achieve that by using alternative letter shapes that are, say, 10 or 20 or 30 points wider than the default shapes. But these shapes can make the lines closer to measure, thus reducing the usage of other mechanisms.
TODO: Is it possible to say which OpenType tables describe these shapes?
Besides mandatory ligatures, Arabic typefaces can include a number of optional ones. These ligatures can be used in justification, because they usually reduce the width of the words.
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- Drop “elongation” from title of this section. It’s one of the mechanisms used for justification.
- Make sure these terms have correct definitions and translations in our glossary: elongation, kashida, tatweel, measure, color, river
- Discussion at ALReq meeting on 28 June, 2016
- Justify Just or Just Justify
- Arabic text justification
- Thomas Milo’s “Arabic script and typography: A brief historical view”
- Tasmeem Manual
- Justifying Text using Cascading Style Sheets (CSS) in Internet Explorer 5.5
- TODO: Improve the images.