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Chapter 4 Text, Graphics, Symbols, and Codes

Chapter 4 Text, Graphics, Symbols, and Codes. Deals primarily with displays that present static information, that is display of visual stimuli that are unchanging or remain in place for a reasonable time. The eye. Aqueous Humor.

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Chapter 4 Text, Graphics, Symbols, and Codes

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  1. Chapter 4 Text, Graphics, Symbols, and Codes Deals primarily with displays that present static information, that is display of visual stimuli that are unchanging or remain in place for a reasonable time

  2. The eye

  3. Aqueous Humor

  4. Sinar cahaya yang direfleksikan objek diterima dan melewati kornea yang transparan dan suatu cairan bening (aqueous humor) yang mengisi ruang antara kornea, pupil, dan lensa. Pupil merupakan sebuah bukaan melingkar yang ukurannya berubah menurut aktivitas otot iris. Pupil menjadi lebih besar dalam keadaan gelap (diameternya sampai 8 mm) dan menjadi lebih kecil jika berada dalam keadaan yang lebih terang (diameternya menurun jadi 2 mm). Sinar cahaya yang yang melewati pupil dan menuju lensa, direfraksi olah lensa menuju ke bagian yang terang, suatu zat berbentuk jel, vitreous humor, yang mengisi bola mata di belakang lensa. Proses Melihat

  5. Proses Melihat (2) Lensa memfokuskan sinar cahaya di retina. Retina terdiri dari dua tipe photoreceptors, rods dan cones. Cones berfungsi ketika ada iluminasi dengan level yang tinggi, seperti pada waktu siang hari. Rods berfungsi pada saat iluminasi yang diterima rendah, seperti pada waktu malam. Sinar cahaya ketika diserap oleh rods dan cones menyebabkan terjadinya suatu rekasi kimia yang mengakibatkan rangsangan syaraf ditransmisikan ke otak melalui syaraf optik. Otak kemudian menggabungkan berbagai rangsangan yang diterima dan kemudian memberikan kepada kita, manusia, kesan visual dari dunia luar.

  6. The eye • Lens - Focusing - Accommodation • Vitreous Humor - Shape • Retina - Rods: black & white, night vision - Cones: color, day vision - Fovea: sharpest vision (concentration of cones) • Cornea • Protection • Focusing • Aqueous Humor • Shape • Nutrition • Iris • Light control • Focusing • Optic Nerve - Nerve signals to brain - Optic Disk: blind spot • Eye Muscles - Eye movement - Convergence

  7. Visual Acuity Visual acuity is the ability to discriminate fine detail and depends largely on the accomodation of the eyes.

  8. Acuity usually is measured in terms of the reciprocal of the visual angle subtended at the eye by the smallest detail that can be distinguished. The visual angle (VA) is measured in minutes of arc or in second of arc. VA (minutes) = [3438 x H] / D H = height of stimulus or detail D = distance from eye “Normal” VA is 1.0, depend on type of target The higher the acuity score, the smaller the size of the detail that can be resolved.

  9. Visual Angle of Familiar Objects Object Distance Visual Angle Sun 93,000,000 mi 30’ Moon 240,000 mi 30’ Lowercase pica type reading distance 13’

  10. Snellen Acuity In clinical testing of acuity with letter charts, an observer is usually 20 ft or 6 m from the eye chart. Acuity is expressed as a ratio. 20/30 vision :this indicates that the person tested can barely read at 20 ft what a normal person can read at 30 feet. 20/20 vision : The person can read at 20 ft that a normal person can also read at 20 ft = normal vision

  11. Minimum separable acuity • Smallest space eye can detect between parts of a target (visual object). Also called gap resolution.

  12. Contrast Sensitivity Visual displays refer to any visual presentation of information. A negative contrast display has dark information presented on a lighter background. A positive contrast display is just the opposite, with light information presented on a darker background. Because the background space usually controls the perceived brightness of the visual display, negative contrast displays appear brighter to the eye, causing a smaller pupil size. Conversely, positive contrast displays lead to larger pupil sizes, potentially decreasing iris fatigue.

  13. The fact that we perceive a difference is very important for an understanding of how our visual system works (spatial frequency). • Modulation contrast (Michelson contrast) C = (Lmax-Lmin) / (Lmax+Lmin) • Evans & Ginsburg (1985) : contrast sensitivity is a better predictor than standard visual acuity of people’s ability to discriminate highway signs.

  14. Text : Hardcopy Human factors criteria related to text presented by any means (books, magazine, news paper, computer screen,etc): • Visibility : The quality of character or symbol that makes it separately visible from surroundings. • Legibility: The quality of characters allowing reader to quickly and positively identify characters. This depends on stroke width, form of characters, contrast, and illumination on page. • Readabilty:The quality of print allowing rapid recognition of words, word groups, etc. This depends on character spacing word spacing line spacing character area/background area ratio

  15. Typography • The term typography refer to the various features of alphanumeric characters, individually and collectively (arrangement, style, appearance of type, etc). • Considerations using typography: • non-optimal viewing conditions • changes in accommodation (near/far) • interruptions & distractions • several age groups

  16. Stroke Width :Ratio of the thickness of the stroke to Height of letter or numeral

  17. Stroke width (2) • The effects of stroke width are intertwines with nature of the backgraound (black on white versus white on black, called irradiation), and with illumination. • In general, black on white letters should be thicker (have lower ratios) than white on black ones.

  18. Width to Height Ratio for Distance Reading Ws = 1.45 X 10-5 X S X d HL = Ws / R Ws = stroke width S = denominator of snellen acuity score D= reading distance HL = letter height R = stroke width-to-height ratio of the font, expressed as a decimal proportion (0.2 for 1:5)

  19. Text : VDT ScreensReading text from Visual Display Terminal or Visual Display unit/computer screen, is not the same as reading text from hardcopy.People proofread about 20-30% slower when material was presented on a VDT than when it was presented on hardcopy. The reason: image quality of dot-motrix.The higher the resolution of the screen, the less the difference between VDT and hardcopy.

  20. Text : VDT Screens (2) Arrangement (or layout) to reduce complexity

  21. Symbols • Criteria for Selecting Coding Symbols • Recognition • Matching • Preferences and opinions

  22. Right lane ends ahead. If you are in the right-hand lane you must merge safely with traffic in the lane to the left. Pavement is slippery when wet. Slow down and drive with caution. Bump or uneven pavement on the road ahead. Slow down and keep control of your vehicle. The road ahead is split into two separate roads by a median. Keep to the right. Each road carries one-way traffic.

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