1. IS502:Multimedia Design for Information System Digital Representation for Multimedia
Presenter Name: Mahmood A.Moneim
Supervised By: Prof. Hesham A.Hefny
Winter 2012
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2. Introduction In this lecture we look at :
images, starting with 1-bit images, then 8-bit gray scale images , then 24-bit color images.
Bitmap versus vector graphics.
Image representation
Video and animation representation
Audio representation
Text representation
Give a brief overview of the presentation. Describe the major focus of the presentation and why it is important.
Introduce each of the major topics.
To provide a road map for the audience, you can repeat this Overview slide throughout the presentation, highlighting the particular topic you will discuss next.
By Mahmood A. Moneim

3. 1-bit images
Images consist of pixels – picture elements in digital images.
1-bit image consist of 0 or 1 bits only and thus is the
simplest type of image. Hence It refer to binary image.
Also called monochrome image, since it contains
no color.
if an image has dimension 640X480 then it requires 38.4 Kbytes of storage.
By Mahmood A. Moneim

4. 8-bit Gray-Level Images
Each pixel is represented by a single byte.
The entire image can be thought of as a two-dimensional array of pixel values.
We refer to such an array as a bitmap.
Image resolution refers to the number of pixels
in a digital image.
By Mahmood A. Moneim

5. 8-bit Gray-Level Images
We can think of the 8-bit image as a set of 1-bit bitplanes, where each plane consist of a 1-bit representation of the image at higher levels .
Each pixel is usually stored as a byte (0-255)
So a 640X480 grayscale image requires 300KB.
By Mahmood A. Moneim

6. 24-bit Color Images
In a color 24-bit image, each pixel is represented by three bytes, usually representing RGB.
Each value is in the range
A 640X bit color image would require KB of storage without any compression
An Important point of
note is that many 24-bit color images
are actually stored as 32-bit images ,
with the extra byte of data for each
pixel storing an α (alpha) value
representing special effect information.
By Mahmood A. Moneim

7. Image Representation
Images may be modeled as bitmaps or vector graphics
Bitmaps: A bitmap is an array of logical pixels (stored color values) that can be mapped directly to the physical pixels on the display
By Mahmood A. Moneim

8. Image Representation
Vector Graphics: The image is stored as a mathematical description of a collection of individual lines, curves and shapes making up the image, which requires computation to render it
Rendering: Generating the pixels from the model
By Mahmood A. Moneim

9. Image Representation
Using vector graphics, the image is represented in only 284 bytes
Using bitmap, if the image is of a square of width 45mm and we use 24-bit for each color at a resolution of 72 pixels/inch, we need a total of 48 kilobytes .
By Mahmood A. Moneim

10. Image Representation
Vector graphics are often smaller than bitmaps, are resolution-independent and can be scaled without loss of quality, but they are only suitable for certain sorts of synthetic image, not photographs
By Mahmood A. Moneim

11. Image Representation
When scaling up an image in vector graphics format, curves remain smooth whereas in bitmap format they become blurred
Original image
Original image
By Mahmood A. Moneim

12. Video and Animation Representation
Displaying moving pictures depend on the phenomenon known as persistence of vision: A lag in the eye’s response to visual stimuli resulting in “after- images” being seen briefly when the stimulus is no longer present
If still images are presented to the eye at a rate above the fusion frequency (around 16 to 40 pictures/sec), we experience a continuous visual sensation
Thaumatropes Video
By Mahmood A. Moneim

13. Video and Animation Representation
A sequence of frames has two types: Live-action: Sequences recorded from real life (video) Animation: Artificially created (drawn) sequences
Video frames are stored digitally as bitmapped images which require extensive compression Example: A frame that is generated by a Digital Video camera is 720 pixels wide x 576 pixels tall (PAL) and should be displayed at a rate of 25 frames/sec With no compression, each pixel requires 24 bits for color, so each frame would be 720 x 576 x 24 ≈ 1 MB and each second of video would be 25 x 1MB = 25 MB, so a 10 minute video will take ~15 GB
Because of the large size of video data, compression is always applied such as the MPEG-4 standard
By Mahmood A. Moneim

14. Video and Animation Representation
Animations may be captured from external source or created in a computer
Animations can be created using vector graphics (cartoon style) which results in small files compared to video
By Mahmood A. Moneim

15. Audio Representation
Sound can be represented as a sequence of samples after digitization
Audio File
CD audio is sampled at 44.1 kHz
, higher sampling rates are sometimes used
Audio delivered over the Internet is compressed, often using the MP3 codec
Digital representation of audio facilitates editing (such as slowing down the music by adding samples)
By Mahmood A. Moneim

16. Text Representation
A character set is a mapping from characters to character codes
Unicode is a character set capable of representing text in all known languages
A font is a set of character shapes, called glyphs, which define how a character is displayed
By Mahmood A. Moneim

17. Text Representation
Many aspects of layout must be controlled when text is displayed
Images can only be displayed in one way whereas the same words can be arranged in many different ways
By Mahmood A. Moneim

18. Microsoft Engineering Excellence
Questions?
By Mahmood A.Moneim
Microsoft Confidential