ITGS

Multimedia

Multimedia

• Multimedia– Computer graphics, video, audio and

interactive applications– Used extensively in entertainment, science

and journalism

• Bitmap graphics (raster graphics)– Images that are composed of a rectangle of

small dots called pixels• Photographs are made up of pixels

– Resolution• The higher the number of pixels in an image, the

more detail the image can hold.

Bitmap Graphics– Image editors

• Used to improve the appearance of a photo (Adobe Photoshop)

– Editing tools• Cropping - taking a subsection of a photograph and removing

everything else• Scaling - increasing or reducing the size of an image• Cloning - the process of copying one part of an image into

another part of an image• Selection tools - very useful for highlighting just part of an

image so that alterations are applied to only that area instead of the whole image

• Layers - commonly used when making composite images– They allow several images to be stacked on top of eachother

• Filters - effects features• Composite image - when editing tools are used to combine

tow or more images– Computer generated imagery - (CGI) - a combination of

photographs and computer-generated images

Social Impacts• Social impacts

– It has become harder to detect alterations as editing software and techniques become more sophisticated

• Health and Leisure– Altering the appearance of models to make them conform to a more

stereotypical image of attractiveness– This creates unhealthy eating practices and negative body images in

young people

• Legal impacts– 1994, O.J. Simpson case

• Simpson’s defense lawyer complained that a pair of rare, expensive shoes whose prints had been found at the crime scene were photoshopped into another photo of Simpson (wearing them)

• TIME magazine ran a photo of his mugshot which was digitally darkened to make him look more sinister

• Political impacts– 2004 Presidential election - a magazine combined two photos

Scientific Impactstogether - one of John Kerry in the 70’s and one of Jane Fonda

at a protest of the Vietnam War• The public believed the photo, but it was a composite• Other examples of composite photos made to make

situations look more dramatic– Scientific impacts

• 2005 - South Korean researcher Dr. Hwang Woo Suk resigned from his position at Seoul National University after allegations that he faked images showing research results

– He digitally altered images to show 11 stem cell colonies, when there were only 3

– Spotting digital fakes• The use of copy and paste and cloning tools often leaves tell-

tale patterns of repeated pixels in an image– When not clearly perceptible, they can be detected by

special photographic analysis software» It scans images looking for regions of similar color and

content - the greater the similarity between 2 regions of an image, the greater the chance of manipulation

Image Storage» Lighting inconsistencies can also be detected

• Image Storage– All bitmap images are stored in the computer as a

rectangular grid of pixels• Resolution - refers to number of pixels in the grid

– Higher resolution - more detail can be stored in the image

– Manufacturers of digital cameras quote the resolution in megapixels - the total number of pixels in the image, by the millions

• Anything above 8 megapixels is good– Computer screens have a lower number of pixels per

inch than cameras

• Bit Depth or Color Depth– The number of bits used to store each pixel in the image

• The higher the bit depth, the more colors an image can contain, but the more storage space it will require

Bit depth• True color

– The most common bit depth for photographs» 3 bytes of storage are used for each pixel» In each pixel, 1 byte = red, 1 = green, 1 = blue

• Storage requirements– Width x height x bit depth = storage

requirement

• Compression– Most file formats use some form of compression

to reduce redundant, repeated data in images and reduce the amount of storage required

• Lossless Compression– Looks for repeated patterns of data and stores them in a

manner which requires less space, but it still allows the original data to be exactly restored

Lossless Compression

All bitmap images are composed of grids of pixels (left)

Each pixel represents a binary color value for the computer to display (right)

Lossless compression

The values on the left represent each pixel value

On the right, the data is compressed to tell the computer that there are 8 pixels with the value 0 (blue), etc.

Lossy compression• Problems with Lossless Compression

– Lossless compression is less effective at compressing photographs, because they have a large variety of subtle shades rather than solid blocks of color

• Lossy Compression– Sacrifices image quality in return for storage space

» It discards data that ‘probably’ won’t be missed by the viewer

» For example, if two adjacent pixels are almost the same color in an image, lossy compression might make them exactly the same

– Problem: once data has been discarded, it cannot be retrieved again, so quality loss is permanent

» Repeatedly editing an image, saving in a lossy format, editing and sving again will result in a gradual loss of quality at each save

– Lossy format: jpeg; Lossless = tiff

PPI and DPI• Pixels per inch - how many pixels are

displayed in each output, whether on screen or on paper– This determines the physical size of the output and

how sharp it will be• Most computer screens are 96 PPI• Most commercial and professional printers require images

that are 300 PPI

• Dots per inch - printer resolution - the number of ink dots that a printer produces when creating an image– Printers only have CMYK (cyan, magenta, yellow

and black) ink colors, so to produce all possibly colors, they mix inks in the same spot on the paper

Vector Graphics• Vector graphics - composed of objects rather

than pixels (object-oriented graphics)– Each object is stored as a series of mathematical

equations that define its starting point, ending point, and path, along with info about color and style

– All objects remain separate in the image, so they can be edited, scaled, repositioned and recolored independently at any time

– Most software supports only bitmapped images, so vector editors can usually export images in bitmap formats

– Advantage: because they are defined mathematically, vector images can be scaled as large as required without any loss of quality

– Disadvantage: because they are so complex, vector graphics require computers with faster processors to perform the number of calculations necessary

3D Vector Images• 3D Vector Images - Vectors are the primary

method of creating three dimensional imagery– CAD - software used by architects and engineers to

create 3D technical drawings of products in development

• It can be viewed in detail before it is even created• It enables them to test physical properties such as weight,

strength and material

• Graphics in the Movies– CGI (computer generated imagery) is often used to

create animations or special effects• Motion capture - the actor wears a special suit with

markers at key points such as hands, arms, legs, head. As he/she moves, the markers can be detected by a camera connected to the computer, allowing it to know the position of the main parts of the body and build up a wireframe skeleton inside the computer

Movie graphics

• Textures - it’s impossible to create the required level of detail purely with 3D vectors, so the overall shape of objects is modelled using a simple 3D shape and then a 2D bitmap texture is applied to give a deeper and more life-like appearance

• Rendering or ray tracing - after properties such as reflections and light are added, the scene can be rendered to calculate how the light in a scene behaves bouncing off objects and into the virtual camera. Producing such high quality images for film and television can take hours for a single image, even on very fast computers.

– Render farms - hundreds or thousands of computers working together to improve processing speed for this type of entertainment

Common video formats

AVI - Audio Video Interleave

Lossy; early video format

MOV Used in Apple’s quick time system

MP4-Motion Pictures Expert Group 4

New file format; more efficient lossy compression

WMV-Windows Media Video

Microsoft proprietary; supported on Windows

Common audio formats

AAC-Advanced Audio Coding

Apple iTunes; lossy compression, supports DRM

FLAC-free lossless audio codec

Open file format, lossless

MP3-MPEG Audio Layer 3

Lossy format; the format that changed the music industry in the 90s

WAV - Wave Common, supported by all audio hardware and software

WMA Windows only; lossy, can be streamed

Common image formats

BMP-Bitmap image Windows Paint Only

TIFF-tagged image file format

Lossless; used in professional printing

GIF-Graphics Interchange Format

Common on the web; supports transparency

PNG- Portable Network Graphics

Lossless, open format, supported by most browsers

JPEG-Joint Photographic Experts Group

Most common lossy file format; produced by all digital cameras; common on web

Common image formats

PSD-Photoshop Document

Photoshop proprietary

RAW-raw image Raw image formats produced by digital SLR cameras. They maintain more color info than JPEG files and include metadata such as shutter speed and aperture.

SVG-Scalable Vector Graphics

Format for storing vector graphics; actually XML test files, meaning they can be edited in normal text editors

Digital Audio• Sounds and music projects are now produced

entirely digitally– Sound is recorded, converted into digital data

(digitized) - and loaded into audio editing software, where it can be manipulated using a wide range of effects and filters

• Most audio editing software represents sounds graphically as waves, and allows sections to be selected, cut, pasted and moved freely

– Sample rate or sampling frequency - determines the quality of a recorded sound

• Analog data captured by a microphone must be converted into digital data for the computer to process

• Sample rate determines how many times each second a digital sample of the analog data is taken

– More frequent samples means the digital sound will be closer to the original

» CDs are high in sampling quality = 44,100 Hz

Bit rate– Bit rate - a value displayed in some music players; the amount of

data used to represent each second of audio• Higher bit rate = larger number of digital values to choose from when

taking a sample

• MIDI - Musical Instrument Digital Interface -communication standard for music devices, computers, and music creation software– MIDI devices have built-in recordings of different instruments played

at different notes and pitches• MIDI music files contain only the instructions for how to play the

instruments, not the actual sound

• Digital Video– Moderately advanced video editing software allows the editor to add

several video and audio tracks to allow smooth fades between videos and to provide separate audio layers such as dialog, music and background sound

• Chroma key - (green or blue screen) effects allow part of a video image to be replaced with another image or video source by removing specific colors

• Morphing - a source image is slowly transformed into a second image over a series of frames

Codecs• Codecs-needed to play compressed audio or video data on a

computer– (compressor decompressor) is a piece of software which tells

media players how to decode the particular compression format used by that video or audio data

• Streaming media - video or audio that is played while it is being downloaded from the internet– Streaming media systems download a small part of the media

into a buffer, which is played while another section is downloaded and loaded into the buffer

• Intellectual property– Refers to non-physical creations such as stories, music, works of

art and computer software• Copyright law provides protection against use of this intellectual

property by unauthorized users– Copyright is automatically obtained by the author of a work when it is

created - there is no registration or application process involved– Intellectual property refers to the work or idea itself, not the physical

media containing it» Example: making a film adaptation of a book is a breach of copyright

Fair Use• Fair use

– Some countries allow exceptions to copyright laws under certain limited circumstances

• Purpose is important– Educational fair use: can’t copy full copies of a whole book

• Impact on the copyright holder: will he/she lose money?

• Enforcing copyright– Watermarking - photographers and artists insert a semi-

transparent image , such as a name or logo, into the piece that makes it hard to remove but still easy to view the image

• Free licenses– Licensing your work freely for non-commercial use

• Creative Commons - free licnesing for non-commercial purposes, requiring attribution

Citing SourcesSources of material should be citedNever assume everything on the internet is free from copyright