1. Vector Graphics Digital Media Module – week 3

2. Graphics What sorts of computer graphics are there? How do they differ? What can we use them for? How can we create them?

3. Session Introduction Today’s first topic is Vector graphics - sometimes called clip art or drawings or pictures Don’t be misled they don’t have drawn by hand

4. Outline We will look at: –what vector graphics are exactly –why vector graphics are important –how they are created –what they are used for –how they are stored –what their use is in multimedia

5. Introduction to the Nature of Vector Graphics They are a static media, so they don’t change with time That isn’t to say that we can’t appear to make them change but they don’t change by themselves There are three sources of vector graphics: –Human-created drawings –Program or script generated drawings –Computer converted scans or digitised printed material

6. Vector Graphics The first major division of graphics files is the vector Literally a list of vectors (lines with length and direction) making up the graphic (image) –They may enclose areas for form shapes

7. Maths and Vectors The mathematical nature makes vector graphics suitable for: –technical drawings –outline drawings – cartoons –diagrams –flowcharts –graphs

8. Vector Graphics - 2 Even something as simple as an arrow may be a vector graphic Their content is normally characterised by shapes bounded by lines either straight or smooth curves – otherwise known as splines –the lines may be a different colour – line colour as opposed to fill colour Their colouring is normally characterised by areas of single colours

9. Spline-based Curves A spline is a mathematical representation of a curve - used in most drawing programs –defined by a series of anchor points for the curve –can manipulate the curve by moving the two control handles on each anchor point except the end points of the line which have only one –the program can ensure that the curve passes through the anchor points smoothly if required

10. Spline-Based Curves

11. Conclusion for Nature of Vector Graphics They are a static media There are five main uses for vector graphics: –technical drawings –outline drawings – cartoons –diagrams –flowcharts –graphs They are a just lines and shapes

12. Introduction to Vector Files What information the files actually hold What determines their size First we’ll consider types of item held in vector files

13. Drawings Sets of shapes created by a drawing or CAD application Consist only of lines Lines and enclosed shapes may be coloured Macromedia Freehand, Adobe Illustrator, MS PowerPoint, Corel Draw, Autodesk’s AutoCAD, etc.

14. Drawings - 2 May also be creatable by the MM authoring SW Supplied ready-drawn as clip-art One set of shapes for all sizes of reproduction –Very compact file storage –Relatively easy to alter

15. Graphs Shapes created by a Graphing application Consist only of lines –lines and enclosed shapes may be coloured MS PowerPoint, Excel, etc. May also be creatable by MM authoring SW One set of shapes for all sizes of reproduction –Very compact file storage –Relatively easy to alter

16. Digitising Digitised Drawings –Shapes created by using digitising tablet to pick out significant points – such beginning and ends of lines –Used within drawing or CAD package to create technical drawings

17. Size The size of a vector file – the amount of disk space it needs depends on two things –The complexity of the “drawing” –The efficiency with which the vector information is held in a particular format This may be related to the versatility of the format If it is program specific it may be quite compact If it is generic – designed by a committee perhaps – it may have to incorporate more types of information in less compact forms

18. Conclusion for Vector Files Hold information about vectors and colours Complexity determines their size

19. Introduction to Specific File Formats We’ll consider the need to choose the file formats that you will use carefully Common file formats To use a vector graphic that already exists your SW must be able to handle the format in which the graphic is saved

20. Vector File Formats There are numerous formats; some common ones are: –WMF, EMF, CGM, DXF, CDR, AI, FH10, PICT, PS, FLA and SWF Many vector graphics formats permit the saving of embedded image (bitmap graphic) within the file

21. Vector Graphics File Formats - 1 Windows metafile -.wmf –Created by Microsoft for drawings produced by Office mini-apps, i.e., Draw, and Office clip-art –updated enhanced version, Enhanced Metafile -.emf Computer Graphics Metafile -.cgm –Long established standard for graphics –Many component parts but many variations permitted

22. Vector Graphics File Formats - 2 Drawing Exchange Format -.dxf –AutoCAD’s open format –Designed for CAD drawings –Also Drawing -.dwg AutoCAD’s native format CorelDraw -.cdr –Proprietary format –Also newer open standard.cmx format, used for CorelDraw clip-art –.cdx CorelDraw compressed and.cpx Corel CMX compressed

23. Vector Graphics File Formats - 3 Adobe Illustrator -.ai –Proprietary format Macromedia Freehand -.fh9 (also.fh8,.fh5, etc.) –Proprietary format Macintosh PICT Files -.pic or.pct –A hold-all format that can be used for bitmaps or vector graphics Postscript -.ps –Adobe’s page description language –Can include a bitmap in the encapsulated (.eps) version

24. Vector Graphics File Formats - 4 Macromedia Flash -.fla –Proprietary format proposed for adoption as WWW standard –Vector graphics drawing package that also animates and can incorporate audio and add interactivity –Designed for the Web – produces small files –Native Flash files -.fla – are editable files that contain the material Flash works on –Shockwave Flash files -.swf –the optimised files for web use –Flash will create the Shockwave Flash file

25. We’ll summarise briefly things to bear in mind when using vector graphics Look at where you get them from and copyright implications We’ll consider the need to choose the file formats that you will use carefully Common file formats DrawingsDiagrams/Graphs/Cartoon Compact and easily altered Remember

26. Create them yourself –if you create, you own it Copy them from another source –if you copy, you don’t own it but you may or may not be entitled to use it –if you do use it you must have a clear written agreement that you may use it Where Do You Get Them? When in Doubt, Don’t Copy Buy rights from a stock media house

27. Bitmap Graphics Bitmap graphics are sometimes called bitmap images Commonly photographic and painting images

28. Bitmap Agenda We will look at: –what bitmap graphics are exactly –why bitmap graphics are important –how they are created –what they are used for –how they are stored –what the consequences of using many colours are on storage requirements –what their use is in multimedia

29. Introduction to the Nature of Bitmap Graphics They are a static media, i.e., they don’t change with time That isn’t to say that we can’t appear to make them change But they don’t change by themselves

30. Sources of Bitmaps There are three sources of bitmap graphics: –Human-created Images –Natural Images –Pre-existing Images Normally characterised by far greater variation in colours and shapes than a vector graphic

31. Bitmap Graphics Literally a map of the colours used for each bit (pixel) making up the graphic (image) With no mathematical limitations imposed they can be used for pictures created: –by hand – sketched or painted –from vector graphics packages – by exporting at a specific size and colour depth –from photographs – by scanning –from video – by image capture –directly with a digital camera

32. Human-created Images Paintings or Drawings –patterns of dots created by “Paint” application –Adobe PhotoShop, MS Paintbrush, Corel PhotoPaint, Paint Shop Pro, etc. Even if it consists only of geometric shapes it’s still a bitmapped image if that’s how the package, that creates it, stores it –some packages that normally create vector graphics offer the option of converting the graphic into a bitmap

33. Natural Images Patterns of coloured pixels created by: –scanning a photograph –capturing a still image from a video –using a digital camera Always a bitmap

34. Pre-existing Images Patterns created by scanning: –painting or drawing or hand-writing (no matter how created) –printed matter: text in book or on magazine page - computer printout Always a bitmap –scanned drawings can be converted to vector drawing by special software –sometimes called digitising

35. Conclusion for Nature of Bitmap Graphics They are a static media There are three primary sources of bitmap graphics: –Human-created Images –Natural Images –Pre-existing Images They are a map of the colours used for each pixel making up the image

36. Introduction to Bitmap Files What determines their size What information the files actually hold How this relates to the characteristics of the files What standards there are for the colours used in bitmap images First we’ll consider what bitmap files actually store:

37. Bitmap Files Store the colour value (and possibly various other information) of each pixel (picture element) File size depends on number of pixels in the image AND the number of colours used (and amount of other information) in the image

38. –each pixel must be capable of specifying any of the possible colours –number of colours to be used is specified initially by creator –number of colours may be altered during creation/editing process or finally when saving

39. Bit Depth Bit Depth is the amount of memory needed to store the colour information A single bit can only store a 1 or a 0 So a single bit is used to store Black or White information Any number of bits could be used: –e.g., 4 bits can hold information on 16 colours –Equally 4 bits could describe 16 shades of grey –transparency Information can also be stored

40. Bit Depths for Images 1 bit = 2 colours, i.e., Black and White 8 bits = 256 possible shades of grey or = 256 possible colours But which is it and which 256 greys or colours? Clearly it is important to know File starts with header information which contains such details How many colours can a 24-bit image hold?

41. Conclusion for Bitmap Files They store information about pixels Bit depth is how many bit are used per pixel 24-bit images  16.7 million possible colours (True Colour) today’s multimedia standard is 24-bit, most potential customers have 24-bit graphics cards

42. Common standards What is the de facto standard for multimedia and why? 24-bit images  16.7 million possible colours (True Colour) 48-bit images  281,500 billion possible colours the de facto multimedia standard was 8-bit, since 256 colour video adapters were the best that all potential customers were likely to have

43. Modern standard today’s multimedia standard is 24-bit, most potential customers have 24-bit graphics cards

44. Summary of the Lecture bitmap graphics use pixel information to store an image they enable photographic and painted images to be stored we can create them by: –Painting, capturing or scanning –scanning a photograph or drawing bitmap images are stored with various amounts of colour information: –24-bit 16.7 M, 16-bit 65,536, 8-bit 256