Lecture 3. Comp sci 1033b 04/17/2014
We rely on graphics for: entertainment, explanation, and information. They
visually appeal to us
What is the origin of graphics?
First it was by a nondigital media and then you’d scan the picture into your
computer and save it as a file. Then outside world digital camera. Take pictures
and upload them as a file onto your computer. Then clip art came out and you
could create the images and scenes yourself and save them as a file onto your
Computers only speak binary. They digitize your information into 0s and 1s
(everything including words, images, and sounds).
Digitization: is the processes of translating all of your information in the form of
electrical signals (Analog) into binary digits (digital). They translate all the
information to BITs because that’s the fundamental unit of information a
computer can speak.
Why is that the only language they can speak?
Ans: Because computers are systems that are built from devices that have 2
possible states. On (high volt)=1 or Off (low volt) = 0 .
*there is a temporary memory in the keyboard that has the binary digit codes.
Once you press a key on the keyboard or click on something using the mouse the
information is stored into a temporary space called the RAM. And then the
information is converted from these electrical signals into digital in the CPU.
The CPU decides where to send that information. If it’s a graphic it sends it to
the video card/ graphic card.
Most computers don’t deal with information on the level of bits. They move the
data in packages called bytes 8 bits.
There are 4 numbering systems:
a. Binary – 2 digits stored as 8 in a package (byte).
b. Octal8 digits
c. Decimal 10 digits or values
d. Hexadecimal 16 digits (ABCDEF) How many items can we represent using Binary digits? It depends. If we have : 1
bit : max of 2 values , 2 bits : max of 4 values, and 3 bits : max of 8 values. We
can conclude that we cant represent how many months are there using the 3 bits
system because there are 12 months and we have a max value of 8 with the 3 bit
But , how many items can we have? Measurement of each bit is based on
binary system base (2). Bit is 0,1 max of 2 values.
(2 =y) y is all the possible items that we could have, all possible combinations.
Rule: more bits, more colors available to assign to a pixel.
The process of converting analog to digital is a 2 step process:
1. Sampling measuring the image, breaking the thing into parts.
2. QuantizingHow many discrete values will you use to represent each part of the
Sampling for images:
Sampling the images means how many parts will you break the image up into. So
when an image is taken from a scanner, digital camera or clip art, rows and
columns of squares called pixels appear. Pixels are the smallest image unit, and
thus shows the smallest detail. The more samples taken for a picture, the clearer
the picture becomes because each pixel gets one color assigned to it.
Quantizing for images:
Quantizing an image is how many discrete values (bits) will you assign for each
pixel. This shows the color combinations that we could use depending on which
binary system we use. The more bits; the more colors we can assign to each
pixel.(2 = 16 million colors)
Sampling for words is breaking up the word into letters.
Quantizing for text:
Each letter is represented by 1 byte=8 bits. ( The ASCII CODE SYSTEM). So we
are using an 8 bits system. So there would be 256 possible values.
There are 2 color models:
Additive Color model WEB Subtractive ModelPrinting
RGB brighter than CMYK. CMYK.
Primary colors are red, green, and blue Primary colors are cyan, magenta, and yellow.
Adding light to a black background(Monitor) inUses printing ink. It subtracts or removes colors
order to obtain color shades. from a white background. Commercial print is built on CMYK plates and ink.
Why use RGB instead of CMYK for the web?
1. Cathode ray tube devices such as computer monitor display color with
RED,GREEN, and BLUE light.
2. Mixing red, green, and blue color gives us a wide range of colors of the color
How are colors coded?
We use the 24 bit color representation. This gives us 16 million colors.
Colors can be coded using the RGB code, or hexadecimal code.
The RGB notation:
• Each pixel is represented by 3 values.
• Each value ranges from 0255
• 0 represents no amount, 255 represents max amount.
• We have a maximum of 256 color shades