IT82: Mul timedia. Practical Graphics Issues 20th Feb Overview. Anti-aliasing. Fonts. What is it How to do it? History Anatomy of a Font

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1 IT82: Mul timedia Practical Graphics Issues 20th Feb Anti-aliasing What is it How to do it? Lines Shapes Fonts History Anatomy of a Font Overview Types of Fonts ( which do I choose? ) How to make them look nice Font foundries Chapman & Chapman, chapter 7 2 1

2 Digitizing Pictures Historically, digitizing pictures worked as follows: A picture is scanned (sampled) and the bits of the bitmap set according to what colour wins for that pixel 3 Digitizing Pictures Same principle for text production: Also for vector graphics fi bitmap conversion! 4 2

3 Digitizing Pictures Each bit/pixel set to one of two colours because screens were monochrome (one colour on black) Often the results were not good! So how do we make the results better, in particular with colour monitors that can do greyscale? Also, don t forget that monochrome bitmaps still important today, e.g. for high contrast applications Good design says use strong dark/light contrasts for text on a background Non-colour printing involves just the one colour (black) on white paper 5 Anti-aliasing Richardson, Sections 1.5,

4 (a close-up) 7 Shapes Opaqueness in proportion to coverage of shape 8 4

5 Lines 9 Historically there were no fonts (styles of text) Characters were just characters, displayed on the screen (fixed number of columns and rows) or printer (dot matrix, daisywheel) Fonts Chapman & Chapman, chapter 7 Richardson, chapter

6 Anatomy of a Font sans serif baseline point size ascent descent leading serif Point size is in 72ths of an inch 11 Fonts Not to be confused with character sets! Fonts are different ways (styles) of representing characters e.g. to get the Greek letter alpha, a in Symbol font is displayed as α α can also be obtained as character 03B1x of the Unicode character set Not a 1-1 correspondence between characters and font shapes (glyphs) - different shapes for characters when appearing together e.g. Arabic characters ligatures 12 6

7 Some Common Fonts Arial (sans serif, TrueType) Times New Roman (serif, TrueType) Lucida Console (TrueType, fixed-width) Courier New (serif, fixed-width TrueType) Courier (serif) Genius of Crack (serif, TrueType) Σψνβολ (Symbol, a symbol font) ❿ (Wingdings, a symbol font) 13 Bitmapped Fonts Each font shape/glyph represented as a bitmap Scaling doesn t work Entire font families required (how fonts were used in early word processors) 8 point 10 point 12 point 14 point 16 point 18 point 20 point 24 point 36 point 72 point 14 7

8 Vector-based Fonts Nowadays, vector-based (scalable) fonts have taken over. These are defined in terms of three things: glyphs (straight lines and curves) hints Scalable fonts are converted to bitmapped glyphs as needed (e.g. for rendering on a printer) Aside: Java s fonts in Java2D are scalable fonts These use Unicode as the character set 15 Displaying Fonts Nicely Ways to do this include: Non-fixed-width Anti-aliasing Hinting Kerning (spacing) 16 8

9 Anti-aliasing Text 17 It s not always better: Anti-aliasing Text Here s a 8pt plain A in Times New Roman enlarged antialiased 18 9

10 Hinting Problem: display of small-sized text Digitizing results in un-evenness 19 More examples: 20 10

11 11 Hinting Hinting is the provision of hints as to how to display fonts in certain circumstances. A font may be defined without hints, but having hinting results in a better quality font A Microsoft hint to leave vertical and horizontal strokes solid! 21 Without kerning: With kerning: 22

12 12 Kerning Improves text appearance by changing the spacing of adjacent text (even to the point of overlapping) Done by use of kern pairs A high quality font (such as TrueType fonts) have suitable kern pair settings TrueType fonts may have anything from 100 to 500 kern pairs (150 is typical) 23 Font Foundries: the rivals Postscript A PDL (page description language) for printers Often hardware-implemented in a printer Provides many fonts (more than 20,000) TrueType A collection of high quality fonts Software-implemented (suitable for non-printing uses), converted to bitmaps which are then sent to a printer Other fonts required can be purchased from specialist font foundries. Postscript & TrueType are both designed to produce scalable fonts (for printing) & make use of hints etc. 24