The Science Seeing of process Digital Media. The Science of Digital Media Introduction

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1 The Human Science eye of and Digital Displays Media Human Visual System Eye Perception of colour types terminology Human Visual System Eye Brains Camera and HVS HVS and displays Introduction 2 The Science The of eye Digital Media The Science Seeing of process Digital Media The Science Seeing of process Digital Media The Science Seeing of process Digital Media pticalillusions/illusions.aspx 5 6 1

2 The Science of Eye Digital Media The Science of Eye Digital Media Retina Three layers one converts light to neural signals, one does the image processing and one transfers information to the brain Rods and cones Rods see in black and white Cones create the colour images Red cone detects light around 564 nm, green at 533 nm and blue at 437 nm 7 Fovea In the center of the retina 1 mm in diameter Used for high resolution vision No rods around Makes it easier to see in dark when looking to the side rather than forward 8 The Summary Science of of Digital the eye Media The Camera Science versus of Digital HVS Media (1) 9 Camera and eye are built the same way Image based on light Lens and image sensor Two adjustable parameters Focus With camera: manually moving lens With eye: Cornea let's light in but lens behind it changes in shape and size Aperture 10 The Science Brightness of Digital Media The Science Contrast of Digital Media Subjective measurement Amount of light a display is capable of emitting Black should look black can change as ambient light varies With LCD displays usually affects to backlight luminance Measured with candelas per square metre 11 Luminance levels within an image difference between brightness of objects in an image In displays contrast affects to the luminance that is meant for reproducing a full white pixel Contrast and brightness must be in decent level to make image viewable 12 2

3 Dynamic range and Contrast ratio (1) Dynamic range and Contrast ratio (2) In display means the maximum and minimum intensities that a display can generate Brightest white and darkest black a display can display No common way of measuring measures are not comparable 13 Dynamic contrast ratio is difference in intensity over time Static contrast ratio is a difference between darkest and brightest pixels displayed by the display Intensity of the backlight affects as well Different areas of the screen may be illuminated differently With OLED only static contrast ratio matters 14 The Science Visual of acuity Digital Media Clearness of the vision Light enters the eye Through pupil, then lens and is projected on retina Muscles move eyeball so that image is in the fovea Level of detail eye can actually see from pattern of pixels on a screen Not usually counted separately 200 ppi good enough 15 The Science Angle of viewing Digital Media The angle in which eye tries to get the point of interest reflected to the foval area Usually around 155 degrees vertically and 185 degrees horizontally Camera Means the scene that can be imaged Angle in which you are still able to see the content of the display usually degrees with LCD displays 16 The Perception Science of Digital of colour Media The Science Colour of Digital Media Very often a subjective matter Hue dominant wavelength of the colour Brightness/lightness luminosity of the colour If an object reflects light, this is lightness, if it emits light, this is brightness Saturation pureness of the colour Can be called as white light mixed with hue 17 In additive colour mixing light is added to a dark background Example RGB In subtractive colour mixing a certain method is used for blocking white pixels Example CMYK 18 3

4 The Science Colour of gamut Digital Media The Science Colour of in Digital displays Media A certain part of the colour map that a device can present In 1931 Commission Internationale de l'eclaraige (CIE) developed the chromaticity diagram 19 s emit or reflect light with different strengths of three primary colours Ambient light has always an effect as well as it reflects off the display With LCD displays the gamut is related to the emitted spectrum of the backlight 20 The Science Colour of depth Digital Media The Science Refresh of rate Digital (1) Media The number of colours the display can display Bits LCDs 6-bits per pixel causing a 18-bit colour image Dithering increases the amount of colours Dithering artificially changing shade of a colour during a refresh of the display Causes 24-bit image 21 This means the number of times a display is repainted per second Expressed in Hertz Should be twice as much as the viewer's refresh rate 22 The Science Refresh of rate Digital (2) Media Detects and processes a moving object in about 120 ms requires 20 images per second for blurring to start Too slow refresh rate causes flicker effect Meaningful with CRTs With LCDs flickering does not occur because liquid crystals merely act as shutters against the backlight 23 Typical display types Terminology related to displays and visual system Introduction 24 4

5 The Cathode Science Ray of Digital Tube (CRT) Media The Liquid Science Crystal of Digital Display Media (LCD) The most common display until last years No fixed amount of pixels Image can be very good Usually big in size Not as bright as LCD displays Technology Electron guns send beams of electrons Stimulating a layer of phosphor that are the pixels of a CRT (red, green and blue) Magnetic field and deflection of the electrons form the image 25 Liquid crystals are sandwiched between two polarizing filters Backlight travels through the first filter while electrodes create a current that travels through liquid crystals and forces those to align in a certain way Alignment of the liquid crystals creates the intensity and the colour of light visible finally on the screen 26 The Plasma Science Display of Digital Panel Media The Organic Science Light of Emitting Digital Media Diode (OLED) High contrast ratio, panel can be big Popular in public places Contains cells that are filled with ionized gas Glows when electrical field around it is charged Pixels can be only on or off so no grey levels are possible to create Yet quite small displays Can be even flexible Do not use backlight Self illuminated materials Less power consumption Very good contrast ratio, colour reproductions and response time The Science Resolution of Digital Media The Science Response of Digital time Media CRT no resolution LCD, OLED, Plasma amount of pixels is fixed (pixels horizontally and vertically available) HDTV has made this especially important Resolution is not fixed quantity For that reason displays with same resolution but with different size are not comparable 29 A time it takes for pixels to move from one state to another Faster response time means smoother image transitions e.g. In sports Before this measure measured time for turning display on, off and on again 2005 manufacturers changed this for considering grey-to-grey changes Good LCD displays claim to have 2 ms response time 30 5

6 The Science Screen of Digital size Media The Science Summary of Digital Media Diagonal size of the screen in inches With CRTs there was screen size and viewable area separately Different LCD display manufacturers handle this differently EITHER viewable area OR actual screen size is a very complex system Camera is a simpler but similar system Different aspects have to be taken into account when designing displays Depends on technology