1. Dr. Jim Rowan ITEC 2110 Chapter 3
Digital Media
Dr. Jim Rowan
ITEC 2110
Chapter 3

2. Computer Graphics... Arguably a very different viewing media
Forced to look carefully at the processes that move stuff from the real world to the computer... AND BACK!
Usually consumed on a fairly low resolution monitor
Graphic images work very differently on a screen than when in print
can be seen with lights out
will be viewed from different resolution monitors
viewing angles are different
reflections off screen... magazine (gloss)

3. Computer Graphics
Complex enough to be arguably an enabling technology not just a single thing
WWW
fostered the shift from text based media
has begun to develop its own visual vocabulary
Ways to model computer graphics
(there’s a numeric model of a real-world phenomenon)
bitmapped images
vector graphics
each with their advantages and disadvantages

4. But first: How to display a bunch of data?
This is a field of study all by itself that includes computer graphics, cognitive science and psychology
For example: Different graphing forms
pie charts
bar charts
use color for delineation?

5. Designing information display
How to lie with statistics
Edward Tufte, Yale University
Visual Display of Quantitative Information
Envisioning Information
Visual Explanations

6. Computer Display types
Now... all are rectangular arrays of pixels
Not always that way
Early graphics (1976) used a “steerable” electron gun, not raster graphics
Since then...
we have moved away from electron gun

7. Internal and External graphics models
Internally an application keeps a numeric model
Externally an application must project this internal model onto a bitmapped display
This process is called “rendering”
An application must also project this internal model onto a storage model to be able to store and recall it later

8. Two approaches to graphic modeling
Why two approaches?
drastic size differences
each was good for its type of image
Bitmapped graphics
grandfathered name... more like pixel mapped graphics
Vector graphics
more like object graphics because you describe objects using vectors (formulas)
a line is defined by slope, length & position
a circle is radius & position
a square is length of side & position

9. Bitmapped graphics... Logical and physical pixels
images are modeled internally as an array of pixel values... the logical pixels
physical pixels are the actual dots on screen
Moving from logical and physical pixels
called rendering
may be different size, shape and different resolution
will probably require clipping and scaling to move from logical to physical pixels

10.
A true bitmapped image is black and white
Each logical pixel is represented by a single bit

11. When color came along it borrowed the idea...
except that each logical pixel became a 3 byte
RGB specification instead of a single bit

12.
...
for 1080 more bits...
255
2550

13. 72 bits in the color table 100 bits in the pixel map 172 bits total
Question:
With 2 bits encoding the color, if we expanded the color table, how many colors could be represented?
255 00 01 10

14. Vector graphics
Internal model is very different than bitmapped graphics
Images are described as mathematical equations
Rendering is very different
must translate EQUATIONS to physical pixels
not simply clip or scale
must compute the array of physical pixels from the equations

15. bitmapped graphic
vector graphic
Here are two images, blue squares
Both are displayed at 72 pixels per inch
Both are 1024 X 1024 pixels in size
Each with 3 byte (24 bit, millions of colors) color encoding
Which would be bigger?
Why?

16. bitmapped graphic
vector graphic
Here are two images, blue squares
Both are displayed at 72 pixels per inch
Both are 318 X 318 pixels in size
Each with 3 byte (24 bit, millions of colors) color encoding
Which would be bigger?
Why?

17. Bitmapped/Vector Graphics
Bitmapped image size is set by
size, resolution and color resolution
not affected by contents
Vector graphics size is set by
the contents of the image
the more complex, the larger the file gets
resolution does not affect the size of the file

18. Bitmapped/Vector Graphics
Selection of objects in the image
vector is easy, objects are described by mathematical equations
bitmapped, no objects, just pixels
Special effect (like blur) differences
bitmapped, easy
vector, first convert to bitmapped, then blur

19. Bitmapped/Vector Graphics
Scaling and Resize
Vector? Simple... change formula
Changes can be made BEFORE pixel values are calculated
Bitmapped? Complicated...
frequently results in artifacts
Why is bitmapped complicated?

20. Original image: 10 x 5
Now make it twice as big
[Draw on image]

21. Original image: 10 x 5
[Draw on image]
Now make it twice as big
What happens if there are
two colors next to one
another?
Strictly duplicate?
jagged edges
Interpolate them?

22. Original image: 10 x 5
To make it 50% larger...
What do you do?
Do you make it
15 x 7? or 15 x 8?
1 pixel => 1? 2?
There is no such thing as
1.5 pixels...

23. Bitmapped <==> Vector
Vector can be converted to bitmapped (rasterized)... this process already exists since you RENDER vectors to display them.
Bitmapped to vector is complicated
Vector is based on shapes but bitmapped does not define any shapes
Software must identify edges and find the shapes.

24. Image layers
Bitmapped and vector graphics use this as an organizational device
In bitmapped graphics
layers are used like digital tracing paper to isolate objects in the image
colors can be separated and manipulated individually

25. Now for some calculations!

26. Size and download speed calculations
How big is the audio file?
44,100 samples per second
16 bit quantization
stereo
3m16 seconds in length
How long to load to youTube over
highest speed dial up connection?
adsl?
How long to download from youTube over

27. Size and download speed calculations
How big is the audio file?
44,100 samples per second
8 bit quantization
stereo
3m16 seconds in length
How long to load to youTube over
highest speed dial up connection?
adsl?
How long to download from youTube over

28. Size and download speed calculations
How big is the audio file?
8,000 samples per second
8 bit quantization
stereo
3m16 seconds in length
How long to load to youTube over
highest speed dial up connection?
adsl?
How long to download from youTube over

29. Show Image: testPageImage.tiff
1574 pixels wide
1987 pixels tall
RGB encoded
8-8-8 bits each
No compression
No table
How Big?

30. Show Image: testPageImage.tiff
Inspect it with mac cmd-I
Open image with hexFiend
How big is it?
What is in it?
Mostly why?

31. Questions?