Essential Concepts In Computer Graphics Lecture 2 PDF

Essential concepts in computer graphics Lecture 2  Pixel A pixel or pel of picture element is the smallest unit of a digital image or graphic that can be displayed and represented on a digital display device Resolution The display resolution or display modes of a digital television, co...

Essential concepts in computer graphics Lecture 2  Pixel A pixel or pel of picture element is the smallest unit of a digital image or graphic that can be displayed and represented on a digital display device Resolution The display resolution or display modes of a digital television, computer monitor or display device is the number of distinct pixels in each dimension that can be displayed Width × height = 1024 × 768  Aspect ratio the aspect ratio describes the correlation between width and height. Frequently encountered monitor aspect ratios include 4:3, 16:9, and 21:9. DPI/PPI DPI (dots per inch) indicates the number of dots found within a one-inch line of a scan or print PPI (Pixel per inch) indicates the number of pixel found within a one-inch line of digital screen Both define the resolution, or clarity, of an image  Frames What is Frame? a rigid structure that surrounds something such as a picture, door, or windowpane. frames are rectangular areas meant for inserting graphics and text. They allow users to place objects wherever they want to on the page. In video and animation, frames are individual pictures in a sequence of images.  Saturation In photography, the term 'saturation' describes the depth or intensity of colour present within an image. Saturation is also referred to as 'chroma'; The more saturated an image is the more colourful and vibrant it will appear, less colour saturation will make an image appear subdued or muted. Contrast Contrast describes tones, specifically the relationship between the darkest and brightest parts of an image. If the difference between darkest and lightest portions of an image is vast - for example, if the shadows are very dark and the highlights are very bright - an image is said to have high contrast. Rasterization Rasterization is the technique of taking an image described in a vector graphics format and transform it into a set of pixels for output on a screen. Aliasing the process by which smooth curves and other lines become jagged because the resolution of the graphics device or file is not high enough to represent a smooth curve. The aliasing effect can be reduced by adjusting intensities of the pixels along the line And by increasing the resolution of screen Foreshortening Foreshortening refers to the technique of representing an object or human body in a picture so as to produce an illusion of projection or extension in space. https://artincontext.org/ foreshortening/ Flickering A flicker is the appearance of flashing or unsteadiness in an image on a display screen. This issue can occur when the video refresh rate is too low Halftone Halftone is the reprographic technique that simulates continuous- tone imagery through the use of dots, varying either in size or in spacing, thus Dithering Dithering is a trick many graphic applications use to fool your eye into seeing a whole lot more colors (or grey tones) on the screen than are really there. The computer achieves this optical illusion by mixing together different colored pixels (tiny dots on the screen that make up an image) to trick the eye into thinking that a totally new color exists. Plotter A graphics printer that draws images with ink pens. Plotters actually draw point-to-point lines directly from vector graphics files. A plotter is a computer hardware device much like a printer that is used for printing vector graphics. Instead of toner, plotters use a pen, pencil, marker, or another writing tool to draw multiple, continuous lines onto paper rather than a series of dots like a traditional printer. Display Technologies display device the display device is a term used to describe the device used to view video, images, or text also referred to as a desktop display, a display A display device is an output device for the presentation of information in visual or tactile form example: TV monitor, mobile screen, desktop monitor etc  Video Display Devices Cathode-ray tube Liquid crystal (CRT) Monitor display(LCD) Raster-Scan Displays Light Emitting Random-Scan Displays Diode(LED) Color CRT Monitors Direct View Storage Flat-Panel Displays Tubes(DVST) Plasma Display 3D Display Cathode-ray tube (CRT) Monitors Primary output device – Video monitors Standard design of video monitor: Cathode-ray tube (CRT) Cathode-ray tube (CRT) Monitors © 2005 Pearson Education Display Technologies Cathode-ray tube (CRT) Monitors Refresh CRT Beam of electrons hit phosphor-coated screen, light emitted by phosphor Direct electron beam to the same screen repeatedly, keeping phosphor activated The frequency at which a picture is redrawn on the screen is referred to as the “refresh rate” The maximum number of points that can be displayed on a CRT is referred to as the “resolution” http://en.wikipedia.org/wiki/Display_resolutio n Display principle: Raster Scan Display Principle Random Scan Display Principle © 2005 Pearson Education CRT Display Principles Raster-Scan Displays Based on TV technology Electron beam swept across screen one row at a time from top to bottom Each row is referred to as a scan line © 2005 Pearson Education CRT Display Principles Raster-Scan Displays Picture description(information) is stored in the memory area called as Refresh buffer, or Frame Buffer The number of bits per pixel in the frame buffer is called depth or bit planes Buffer with 1 bit per pixel – Bitmap Buffer with multiple bits per pixel – Pixmap Interlaced refresh procedure Beams sweeps across every other scan line Frame Buffer A frame buffer is characterized by size, x, y, and pixel depth. the resolution of a frame buffer is the number of pixels in the display. e.g. 1024x1024 pixels. Bilevel or monochrome Bit Planes or Bit Depth is displays have 1 bit/pixel the number of bits 8bits/pixel -> 256 simultaneous corresponding to each colors pixel. This determines the color resolution of 24bits/pixel -> 16 million the buffer. simultaneous colors Specifying Color direct color : 8 each pixel directly specifies 8 a color value e.g., 24bit : 8bits(R) + 8 Red 8bits(G) + 8 bits(B) Green palette-based Blue color : indirect specification 24 bits plane, 8 bits use palette per color gun. (CLUT) 224 = 16,777,216 e.g., 8 bits pixel can represent 256 colors Interlaced Scanning To reduce flicker, divide frame into two fields—one consisting of the even scan lines and the other of the odd scan lines. Even and odd fields are scanned out alternately to produce an interlaced image. Flat-Panel Displays A class of video devices that have reduced volume, weight and power requirement compared with CRT Two main categories Emissive Displays Convert electrical energy to light energy e.g. Plasma panels Non-emissive Displays Use optical effects to convert light from other sources into graphics patterns e.g. LCD monitors Plasma Panel Display Plasma panels (gas-discharge display) Contracted by filling the region between two glass plates with a mixture of gases Refresh buffer used to store picture description Firing voltages applied to refresh the pixel positions Liquid-crystal Displays Liquid-crystal displays (LCD) commonly used in small systems Liquid crystal, compounds have a crystalline arrangement of molecules, flow like a liquid Passive-matrix LCD To control light twisting, the voltage applied to intersecting conductors to align the molecules Active-matrix LCD Using thin-film transistor technology, place a transistor at each pixel location For more information about flat panel display https://www.tutorialandexample.com/display-devices-in- computer-graphics/ 3D Display It is also called stereoscope display technology. This technology is capable of bringing depth perception to the viewer. It is used for 3D gaming and 3D TVs. For Example: Fog Display, Holographic Display, Retina Display Etc. Advantages: Impressive Picture Quality Disadvantage: Expensive Binocular Fusion Video Output Devices Desktop Vector display CRT LCD flatpanel Plasma workstation displays(Sun Lab) PC and Mac laptops Tablet computers Wacom’s display tablet Digital Micromirror Devices (projectors) Field Emission Devices (FEDs) Organic Light-Emitting Diode (OLED) Arrays Traditional Input Device (1/4) Commonly used today Mouse-like devices mouse wheel mouse trackball Keyboards Traditional Input Device (2/4) Pen-based devices pressure sensitive absolute positioning tablet computers IPAQ, WinCE machines Microsoft eTablet palm-top devices Handspring Visor, PalmOS™ Traditional Input Device (3/4) Joysticks game pads flightsticks Touchscreens Microphones wireless vs. wired headset Traditional Input Device (4/4) Digital still and video cameras, scanners MIDI devices input from electronic musical instruments more convenient than entering scores with just a mouse/keyboard 3D Input Device (1/2) Electromagnetic trackers can be attached to any head, hands, joints, objects Polhemus FASTRAK™(used in Brown’s Cave) http://www.polhemus.com/ftrakds.htm http://www.isense.com/products/prec/is900/index.htm 3D Input Device (2/2) Gloves attach electromagnetic tracker to the hand Pinch gloves contact between digits is a “pinch” gesture in CAVE, extended Fakespace PINCH™ gloves with extra contacts http://www.fakespacelabs.com/products/pinch.html Display Processor The Display Processor digitizes picture definitions given in an application program into a set of pixel intensity values for storage in the frame buffer. This digitization process is called Scan Conversion. 3D Display Graphics Software Refers to a program or collection of programs that enable a person to manipulate images or models visually on a computer. Graphics Software Classifications Special purpose package Designed for non-programmers No graphics procedures involved Communicate with a set of menus General programming package Designed for programmers Provide library of graphics functions used in programming language  Graphic Standards Agreed specifications which define the common interfaces between computer systems or subsystems  the First quiz will be next WEEK online at 6 p.m For 15 minutes only on this lecture Thank you