Chapter 7 Digital Images and Video Information Technology in Theory By Pelin Aksoy and Laura DeNardis Chapter 7 Digital Images and Video

Information Technology in Theory Objectives Learn how images are digitized Understand the technical features and mathematical calculations that determine the bit size of a digital image Understand the process by which digital video is made Information Technology in Theory

Objectives (continued) Identify the factors that affect the quality of digital images Learn about popular digital image and video file formats Understand the technical attributes of different types of display technologies Information Technology in Theory

Information Technology in Theory Imaging Technologies Traditional camera Invented more than a century ago Captures images with a few simple components: Lens Shutter system Photographic medium such as film Light from the object is focused by the lens, the quick shutter action exposes the film to light, and the image is permanently captured on film The film is then developed and printed on photographic paper Information Technology in Theory

Digitizing Images and Video A digital image is an electronic file made up of a string of 1s and 0s when stored on a medium When the image file is accessed and shown on a display screen or monitor, it is called a pixelized image Composed of many elementary units called pixels (short for picture elements), each containing a single unit of color information A pixelized image is similar to a mosaic Information Technology in Theory

Information Technology in Theory Mosaic Image Information Technology in Theory

Information Technology in Theory Pixelized Images Information Technology in Theory

Information Technology in Theory A Bitmap Image Information Technology in Theory

Information Technology in Theory Vector Graphics Images are represented in the form of mathematical expressions Parameters can include attributes such as orientation, length, width, and color Takes up less storage space than bitmap images Can be easily scaled without degradation in quality and resolution Useful for representing geometric shapes but not effective for photographs Information Technology in Theory

Capturing Color Images Using Digital Cameras Lens system Sensor array Filter system Memory Processor Software Viewing screen Information Technology in Theory

Capturing Color Images Using Digital Cameras Lens system is used to focus the image onto a small sensor array called a CCD (charge-coupled device) array These sensors detect light and produce electricity proportional to the intensity of that light Information Technology in Theory

Information Technology in Theory The CCD Array Information Technology in Theory

The Additive Color Model Information Technology in Theory

The Additive Color Model Information Technology in Theory

Information Technology in Theory Spinning Disk Filter Information Technology in Theory

Image Resolved Into Basic Color Components Information Technology in Theory

Color Palette and Corresponding Binary Codes Information Technology in Theory

Information Technology in Theory Color Gamut The color gamut is directly related to the number of bits assigned per pixel The number of bits allocated to each pixel is called the bit depth Commercial cameras usually have a bit depth of 24, meaning that 224, or roughly 16.7 million, colors can be captured by the camera; “true color” This number of bits is necessary because our eyes are sensitive enough to detect approximately 10 million colors Information Technology in Theory

Spinning Disk Filter vs. Bayer Filter Information Technology in Theory

Calculating Digital Camera Image Sizes Calculate the number of megabytes in a color image captured by a digital camera that can produce images with 2272 x 1704 pixels with a bit depth of 24 Calculate the total number of pixels: Number of pixels = 2272 x 1704 = 3,871,488 Calculate the number of bits: 3,871,488 x 24 = 92,915,712 Convert bits to bytes (8 bits = 1 byte): 92,915,712 bits / 8 = 11,614,464 Convert bytes to megabytes (1MB = 220 bytes = 1,048,576): 11,614,464 bytes / 1,048,576 = 11.07MB Information Technology in Theory

Information Technology in Theory Scanning Color Images Scanner Lens system Sensor array Filter system Processor Mirrors High-intensity lamp Information Technology in Theory

Scanning Color Images (continued) Object to be scanned is placed on a glass plate The object is illuminated with a high-intensity light A scanning head that carries the CCD array is positioned on the object and slides over it as scanning takes place The image is filtered through RGB filters and focused on the CCD array by way of mirrors and lenses The image is quantized and converted to a binary number, then stored as an electronic file Information Technology in Theory

The CCD Array of a Scanner Information Technology in Theory

CCD Array Positioned on a Scanner Information Technology in Theory

Calculating Scanned Image Sizes Calculate the number of megabytes produced at the output of a 1200 x 2400 dpi scanner that has scanned an 8.5 x 11-inch photograph in true color Calculate the total number of pixels: Number of pixels = (1200 x 8.5) x (2400 x 11) = 269,280,000 Calculate the number of bits (true color corresponds to 24 bits): 269,280,000 x 24 = 6,462,720,000 Convert bits to bytes (8 bits = 1 byte): 6,462,720,000 bits / 8 = 807,840,000 Convert bytes to megabytes (1MB = 220 bytes = 1,048,576): 807,840,000 bytes / 1,048,576 = 770.4MB Information Technology in Theory

Some Facts on Resolution Two characteristics determine the quality of digital images: Spatial resolution Brightness resolution Information Technology in Theory

Information Technology in Theory Spatial Resolution Spatial resolution An indicator of the number of pixels per unit length The more pixels per unit length, the higher the spatial resolution The higher the spatial resolution, the better the image quality Affected by image size, viewing distance Information Technology in Theory

Images with Different Spatial Resolutions Information Technology in Theory

Brightness Resolution Related to bit depth and thus the number of colors present in the image Low brightness resolution = fewer colors Changing the brightness resolution changes the number of colors visible in the image Human eye can discern about 24 bits worth of information Dependent upon the device used to capture the image Information Technology in Theory

Information Technology in Theory Monochrome Image Information Technology in Theory

Images with Different Brightness Resolutions Information Technology in Theory

Information Technology in Theory Digital Video Motion is emulated by showing images in rapid succession Visual persistence causes us to see an image for a split second after closing our eyes Human eyes can process approximately 20 images per second before losing the ability to distinguish the transition of one image to another Motion picture industry standard uses 24 frames per second (fps) to create a continuous motion effect Information Technology in Theory

Digital Video (continued) A stick figure drawn in different positions can be brought to life by flipping the pages in rapid succession Information Technology in Theory

Digital Image and Video Formats Digital images and videos could not be captured, stored, and disseminated without the existence of standard formats for compression These formats provide the sets of rules, or protocols, required to compress and view images on display devices such as televisions, computer screens, cellular phones, and PDAs Information Technology in Theory

Information Technology in Theory Image Formats JPEG: Joint Photographic Experts Group GIF: Graphics Interchange Format PNG: Portable Network Graphics BMP: Bitmap Picture TIFF: Tagged Image File Format Information Technology in Theory

Information Technology in Theory Video Formats MPEG: Moving Pictures Experts Group AVI: Audio Video Interleaved WMV: Windows Media Video MOV: Apple (Quicktime) Information Technology in Theory

Information Technology in Theory Display Technologies CRT: Cathode Ray Tube LCD: Liquid Crystal Display LED: Light Emitting Diode Plasma Display Information Technology in Theory

Information Technology in Theory CRT Displays CRT Some computer monitors Traditional television sets Cathode ray tube emits three electron beams Strength and direction of travel is controlled electromagnetically by a beam deflection mechanism Follows a raster scan format Information Technology in Theory

Components of a CRT Display Information Technology in Theory

Information Technology in Theory LCD Displays LCD displays Laptop computers Digital camcorders Gaming devices Cellular phone Use liquid crystal materials, whose properties can be varied by electrical signals An LCD system contains two glass plates that sandwich a liquid with tiny crystals filled in small cells, two polarizing filters on each side of the glass plates, a color filter, and backlighting for illumination from one face of the plates Information Technology in Theory

Components of an LCD Display Information Technology in Theory

Information Technology in Theory LED Displays LED displays Present both still and time-varying digital images Large billboards, concert hall marquees, and sports events An array of tiny light emitting diodes, similar to small bulbs, which emit light of a certain color Information Technology in Theory

Components of an LED Display Information Technology in Theory

Information Technology in Theory Plasma Displays Use an ionized gas that is trapped inside cells between two glass plates Each cell acts like a miniature fluorescent bulb The intensity of light emitted by each cell is controlled with electrical signals, and various phosphors that glow as red, green, and blue painted on one of the glass plates as light from the cells impinges on them The combination of red, green, and blue phosphors forms the color of each pixel in the display Information Technology in Theory

Technical Characteristics of Display Devices Spatial resolution Screen size Pixel/dot pitch Brightness resolution (bit depth) Information Technology in Theory

Measurement of Screen Size Information Technology in Theory

Information Technology in Theory Pixel/Dot Pitch Information Technology in Theory

Information Technology in Theory Projection Systems Film-based projectors LCD-based projectors Digital light processing (DLP) based projectors Information Technology in Theory

Components of a DLP Projector Information Technology in Theory

Information Technology in Theory Summary A digital image file is made up of a string of ones and zeros that represent the pixelized image A pixelized image is made up of rows and columns of pixels, each with a unique color associated with it; a binary code expresses each pixel color Two characteristics that determine the quality of images are spatial resolution and brightness resolution Spatial resolution indicates the number of pixels per unit length (such as inches or centimeters) contained in an image Brightness resolution describes the bit depth, and is the number of different colors inherently present in an image Information Technology in Theory

Information Technology in Theory Summary (continued) Digital video is based on the principle of motion emulation Because the human eye can distinguish at most 20 images per second, the frame rate standard used in the motion picture industry is at least 24 frames per second (fps), which creates the illusion of a perfect continuous-motion effect Formats such as JPEG, GIF, BMP, PNG, TIFF, MPEG, AVI, WMV, and MOV provide the rules for structuring and compressing files that allow us to share and display images and video Information Technology in Theory

Information Technology in Theory Summary (continued) The most common devices for displaying digital images are plasma displays, LCDs, CRT displays, and LED displays The design features that contribute to the quality of display devices are spatial resolution, screen size, pixel pitch, and brightness resolution (also called bit depth) Information Technology in Theory