PBA Front-End Programming

Visual Elements

Visual elements

• Why do we actually need graphics on a website…?

Visual elements

• Just as for colors, a distinct graphic can be part of a corporate identity

• In general, we use graphics for– Illustration– Explanation– Integration

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• ”Many children on the African continent suffer from malnutrition, which can be attributed to poor living conditions, climate changes, civil unrest and population growth”

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• ”Many people find that Puppies are cute, and the prominent eyes, fluffy fur and their childish personalities and behavior support this percep-tion of Puppies”

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• An illustration can – obviously – convey emotions very effectively

• Illustrations should of course be chosen in accordance with the general theme, style and tone of the website

• DNA…?

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• A diagram can help explain complex concepts to the user

• However, the complexity of the diagram need not be reduced (no dumbing-down…)

• Be aware of physical limitations– Printed material: 300+ dpi (dots per inch)– PC Screen resolution: 80-100 dpi

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• A chart can help present quantita-tive data to the user

• Same considerations as for diagrams apply to charts

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• General tips on using diagrams/charts:– Trust the reader’s intelligence– Respect the medium– Tell the truth as you see it– Do not bias your data– Be bold and substantial

• …and test it!

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• Still quite a number of technical issues to consider when using graphics– Display capacity– Bandwith– File formats– Graphics technology– Graphics compression

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• Mainstream PC monitor anno 2011– 24” size, 16:9 format (approx 20” x 12”)– 1920x1080 resolution– Approx 100 dpi– 24-bit color (16.7 mill hues)– Price: Cheap!

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• Other displays– Laptop: 12”-17”, around 120 dpi– Tablet: 7”-10”, around 150 dpi (iPad 132)– SmartPhones: 3”-5”, up to 300 dpi (!)

• Upcoming resolutions– 2560x1600 (even in 10” tablets!)– QFHD/4K, about 10M pixels (later…)

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• No reason to rework e.g. a printed image with regards to colors – we can show all colors!

• May need to rework resolution• Graphics for the web should be

optimised for typical screen resolutions – current recommen-dation is 72 dpi (ppi)

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• Gamma – degree of midtone contrast (?)

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• What can we assume about bandwidth…?• Does ”eyerybody” have a broadband (2+ mbps)

connection now…?• What about mobile broadband…?• Is the ”penetration” of high-speed access

related to e.g. demographic factors?

Visual elements

Visual elements

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• The more graphics on a web page, the longer it takes to load (duh!?)

• BUT – 0,01 sec vs. 0,1 sec, not so

important– 1 sec vs. 10 secs, definitely

important!

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• Even with broadband, care must be taken to optimise physical size of graphics

• Efficient algorithms for compressing images exist – images can thus be stored as:– Uncompressed– Compressed without quality loss– Compressed with quality loss

• Pixel-oriented graphics are called raster graphics

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• Uncompressed– Saved as ”raw” bitmap– Fixed number of bits per pixel (4-24)– Size only depends on image size– .bmp format (on Windows)– Should never be used on the Web!

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• Compressed without loss of quality– Several different algorithms (e.g. Lempel-Ziv-

Welch, or just LZW)– Used in the GIF image format (and PNG)– GIF only supports 256 colors in an image, but the

actual 256 colors can vary– GIF suitable for sharp-edge line art (logo), simple

animations, low-res clips (animated GIF)– Not so well suited for high-quality images

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Good for GIFNot-so-good for GIF

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• Compressed with (possible) loss of quality– Most common file format is JPEG– Offers image quality vs. file size tradeoff– Compression highly dependent on image content

and complexity, can be quite impressive– Can be used for….anything. But where is a non-

perfect image acceptable?• Logo, probably not• Photo, probably ok

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• http://en.wikipedia.org/wiki/File:Quality_comparison_jpg_vs_saveforweb.jpg

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• Progressive JPEG– Loads successively better versions of the image– Useful for providing ”preview” of a large image– Helps on user impatience – NOTE: Not fully supported by all browsers

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• Be aware that JPEG is a no-way-back compression of images!

• Keep the original material uncompressed, and create suitably compressed JPEG versions as needed

Visual elementsSmall graphics for navigation, buttons, logos, simple icons, etcSharp-edge line art, e.g. diagrams

Use GIF/PNG

Small-to-medium images(up to about 200x200)

Use GIF/PNG or JPEG, not much difference in file size

Large images Use JPEG

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• Vector graphics• Defining an image in

terms of geometric shapes instead of pixels

• No inherent resolution!• Image definition is purely

logical (geometric)

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• Creating vector graphics– Mostly useful for creating complex diagrams,

illustrations, etc.– Several professional programs for creating vector

graphics exist (Abode Illustrator)– Most common file format is SVG (Scalable Vector

Graphics), developed by W3C

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• Using vector graphics– Can be converted to e.g. JPEG in any desired

quality, and then published– Adobe Flash supports vector graphics directly– Some browsers support SVG, but not all– Recommendation: Create source material as

vector graphics, publish on the Web as raster graphics

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• Using video on a Website…why?– Some concepts lend themselves

well to ”dynamic” visual presen-tation (complex instructions, sales presentations, etc.)

– Users are used to video on the Web (Youtube)

– Bandwidth is not really an issue anymore

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• Using video on a Website…why not?– Producing high-quality video is

very costly and time-demanding– Users have higher and higher

expectations concerning quality of content

– Bandwidth is still an issue

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• Video uses a lot of bandwidth!• Almost all video formats use

some sort of compression• Other factors– Resolution– Frame rate– Content

• http://web.forret.com/tools/video_fps.asp

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• Examples of video bit rates (MPEG2)– Blu-Ray: 40 Mbit– 1080i: 25 Mbit– 720p: 18 Mbit– DVD: 10 Mbit– Standard TV, 576i: 3-4Mbit– 320x240: 0,5 Mbit

• BUT, can be reduced with quality loss

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• Video compression is also very sensitive to content

• Compression works by storing differences between subsequent frames– ”Car chase” – poor comp– ”TV speaker” – high comp

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• Tips on creating video for the Web– Shoot original video – full quality control– Use close-ups – better for low resolution– Use simple backgrounds – better compression– Steady camera – better compression– Avoid zooming and panning – bad for low

resolution, bad for compression– Use hard cuts, avoid ”silly” effects – bad for

compression

Visual elements