Visual Development Lab

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Computers

Graphics

There are two kinds of computer graphic:

  • Bit-mapped graphics create images pixel-by-pixel and record the state of each pixel in memory.
  • Vector graphics create images by drawing mathematical vectors on screen—"Draw a line from here to there."

Bit-mapped graphics can be manipulated pixel-by-pixel but no element of the graphic can be manipulated as an object: you can select any pixel in a line but you cannot select the line itself. Photographs are bit-mapped graphics and PhotoShop is a bit-map editor. Bit-mapped graphics require less processing, which makes them quicker to display, but they require more memory.

Vector graphics cannot be manipulated pixel-by-pixel but graphical elements can be manipulated as objects: you cannot select a single pixel in a line but you can select the entire line. Create is a vector-graphics editor. Vector graphics require less memory but more processing, which makes them slower to display.

Bit-mapped graphics are difficult to modify but vector graphics are easy to, so always use vector graphics when you can. Thus, you may need to retouch photographs in Photoshop but never use Photoshop to combine several photos on a page or to label or number them. Instead paste the finished photos into a vector-graphics package like Create and create the final document there. Resist the temptation just to finish the job in Photoshop. This will nearly always make more work later, for somebody else if not for you.

File formats

Any application used to create graphics may have its own proprietary format. If you are actively working on a document, or if you want to be able to work on it in the future, you need to save the file in that format. However, proprietary formats have a short life expectancy and you cannot assume that somebody else will be able to read it. For these reasons, finished work should be in one of these formats:

  • PNG (Portable Network Graphics) will compress any image without losing any information. This is the first choice for storing graphics. However, older programs cannot handle PNG files, and PNG does not compress photographs efficiently, so other formats are also needed.
  • TIFF (Tagged Image File Format) is an uncompressed pixel-by-pixel bit-map. It loses no information but it can create large files and is not completely standardized. If you need to store an image without any modification, this is the second choice.
  • JPEG (Joint Photographic Experts Group) compresses continous-tone images like photographs. It will always lose some detail but how much can be determined by the user: there is a trade-off between size of file and loss of detail, a setting that can be optimized for each photograph. Every program that saves JPEG files allows you to set this the degree of compression, often allowing you to preview the results. It is important to make an intelligent decision for the intended use. The variation in size can be tenfold.
  • JPEG2000 is a newer replacement for JPEG that loses less information and can be altogether lossless. It ought to be the best way to store and distribute large files but it is not in general use. Macintoshes come able to handle JPEG2000 files but most computers require some additional software to be installed.
  • GIF (Graphics Interchange Format) compresses graphics containing lines and blocks rather than continuous tones, and with fewer than 256 colours. It is usually appropriate for simple graphics on web pages (although sometimes JPEG works better for those as well).
  • PDF (Portable Document Format) is based on vector graphics, although bit-mapped pictures can be subsumed within it. PDF has several versions ("levels") but if the document does not contain links or graphical effects dependent on specialized hardware, it will be readable on any computer.

PICT files

PICT used to be the most generic graphics format available but the format was restricted to the Macintosh. The format is now obsolescent and PICT files are on the way to becoming unreadable. Never use PICT files unless an application requires them and if you need to make PICT files, keep originals in a generic format.

Converting & resizing

Almost any graphics package will resize images and convert them to different formats but if all you want to do is resize an image or convert its format, or if you need to resize or convert a batch of images, the easiest way is to use ResizeIt.

Graphics engines

On a Macintosh, the applications you use do not create graphics themselves, they control graphics engines in the operating system. OS X has a number of these engines. You rarely need to know anything about them but they work just differently enough to be confusing if you do not understand them. These are the three that you will use most of the time:

  • QuickDraw is the original graphics technology used in the Macintosh. A set of QuickDraw commands written to a file form a PICT document. Before OS X, this was the lingua franca of Macintosh graphics programs. Since every program "understood" QuickDraw, every program could copy and paste PICT files. With OS X, however, a new generation of graphics engine has superceded QuickDraw and PICT. Older applications may use QuickDraw but newer ones will not.
  • Quartz is Apple's next generation of graphics, a subset of the technology that Apple call Cocoa. Quartz takes maximum advantage of modern computers—it can generate three-dimensional graphics for example, and transparent washes of colour—but it does not always create images identical to QuickDraw's. For example, the ends of a line will be shaped differently. For this reason, PICT documents opened in Quartz applications are likely to be changed a bit. Graphics created by Quartz routines can be saved in applications' proprietary files or in the generic formats above but not as PICT documents. Note that some of the more exotic Quartz effects depend on specialized graphics boards built into modern Macintoshes. These cannot be displayed on most other platforms.
  • Open GL is a comprehensive, open-source graphics library that is available for Windows and linux as well Macs, so it is very widely used.
  • PostScript is a language created by Adobe to describe the complete content of pages to be printed by machines. PostScript can generate any image that a commercial printer can print, including any QuickDraw image, but not a few of Quartz's special effects like transparent washes. PDF files use PostScript at their core, so generic PDF files cannot show those either.
  • Java is a cross-platform programming language, not a specialized graphics engine, but it contains a graphics engine that is used by Java applications.

Those are the graphics engines provided by the operating system but applications do not need to use any of them. Microsoft Office supplies its own.

Recommended applications:

*Applications using Cocoa technology are indicated by an asterisk. Cocoa programs are usually easier to use than others, their text is usually easier to read, and they send files to one another more handily.

†Applications supporting LinkBack are indicated by a dagger. If you copy and paste something from one LinkBack program to another, then double-clicking on the pasted object will bring up the original file in the original application, and editing that file will cause the copied version to change. Several text tools work with LinkBack.

Vector graphics

  • Keynote*†
    Apple's simpler & more sophisticated answer to PowerPoint. Opens PowerPoint files and saves in many formats.
  • Pages*
    Apple's simpler and more sophisticated answer to Word. It is excellent for graphical page layouts, and is as compatible with Word files as Word is itself.
  • Numbers*
    Apple's simpler and more sophisticated answer to Excel.
  • Create*†
    An extremely versatile program for general-purpose vector graphics. Does everything but wipe your nose yet is easy to learn.
  • OmniGraffle*†
    For making diagrams: keeps lines connected to shapes no matter where you move the shapes.
  • OpenOffice*/NeoOffice*
    Open-source replacements for Microsoft Office—two versions of the same package—that have separate modules for drawings and for presentations. Here is a comparison of OpenOffice, NeoOffice and Microsoft Office.
  • MS Office
    PowerPoint, Excel & Word contain an assortment of tools and can usually be made to read and write generic formats.
Bit-mapped graphics
  • SnapNDrag*
    Takes snapshots of the screen. Equivalent to Apple's Grab but more flexible and convenient.
  • PixelNhance*
    The simplest way to adjust the overall brightness, contrast, color and sharpness of a photo.
  • Photoshop
    This manipulates photographs bit-by-bit. It is the standard program for professional retouchers but it is complicated. The lab has version 7.
  • Pixen
    A simple bit-map editor designed for tiny objects.
  • VueScan
    Runs the scanner and will also read the scanned file (or any bit-mapped file) and perform optical character recognition (OCR) to convert the file to text. This an unusually competent scanning program with settings that can save a lot of time but it will not be obvious what those settings are. Considering how long it takes to re-scan pages, it's probably worth reading the manual.
  • ImageJ
    An open-source package written by the NIH for scientific manipulations of bitmaps, with innumerable plug-ins available from labs around the world. Do Fourier transforms here. Documentation is on the Web in Wiki form.
  • GraphicConverter
    This is a Swiss Army Knife program. If you need to convert a lot of graphics files from one format to another, or from one size to another, or modify their parameters, this is the program for the job. It is reasonably logical but it is complicated and uses jargon in its menus, so it is indecipherable without a translation. Use the accompanying manual by Henke. It's a PDF file in the same folder as the program.
Combined vector & bit-mapped graphics
  • Preview*
    Views, crops and converts among all generic formats. Use this to extract a portion of a PDF file as another PDF or a JPEG. This is usually the most sensible default application for viewing graphcs, especially PDF files.
  • ResizeIt*
    Resizes images and converts from one format to another.
  • FileJuicer*
    Extracts images from PDF, Microsoft Office, and many files. Its Help menu points to a short web page that explains what it can and cannot do.

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