Download Lecture 3: Images - Dr. Aris Triwiyatno, ST, MT

TKE317 Multimedia
Lecture 3: Images
Dr. Aris Triwiyatno, ST, MT
Dept. of Electrical Engineering
Diponegoro University
[email protected]
Guess
• Original or artificial?
What is Image?
• Citra (image) merupakan suatu representasi spasial
dari suatu objek, dalam pandangan 2D atau 3D.
• In common usage, an image or picture is an
artifact, usually two-dimensional, that has a
similar appearance to some subject—usually a
physical object or a person (wikipedia.org).
– Images may be two-dimensional, such as a photograph or
screen display, or three-dimensional such as a statue.
They may be produced by optical devices—such as a
cameras, mirrors, lenses, telescopes, microscopes, etc.
and natural objects and phenomena, such as the human eye
or water surfaces.
Image Representation
• Image is represented by grid of square
picture elements
s termed pixels
el
pixels
• Citra digital merupakan suatu fungsi dengan
nilai-nilai yang berupa intensitas cahaya
pada setiap pixel pada bidang yang telah
dikuantisasikan (diambil sampelnya pada
interval diskret).
–Nilai intensitas warna pada suatu pixel disebut
pula sebagai aras warna (color
color level)
untuk
level
citra warna
–Nilai intensitas keabuan pada suatu pixel
disebut pula sebagai aras keabuan (grey
greygrey-level
atau greyscale) untuk citra keabuan
Image Representation
Pixel:
- Tersusun dalam M baris dan N
kolom: ukuran citra (M x N ).
- Merupakan komponen citra
terkecil
- Memiliki nilai numerik yang
berkorespondensi dengan sebuah
warna atau aras keabuan (color or
greylevel/greyscale)
Pixel Intensity/Color
• Beberapa referensi membedakan antara warna
(bersifat umum) dengan intensitas (intensitas
digunakan biasanya pada citra aras keabuan)
• Bila intensitas pi
piks
ksel
el di
disaj
sajikan
ikan ddengan
engan 1 bit
• Nilai 0 = Hitam
• Nilai 1 = Putih
• Bila intensitas
• Nilai 00 =
• Nilai 01 =
• Nilai 10 =
• Nilai 11 =
piksel di
disaj
sajikan
ikan dengan 2 bit
Hitam
AbuAbu-abu
AbuAbu-abu terang
Putih
Color
Light and Spectra
- Visible light is an electromagnetic wave in the
400nm - 700nm range.
- Most light we see is not one wavelength, it’s a
combination of many wavelengths.
Figure 9: Light Wavelengths
•
The profile above is called a spectra
Color
Human eye
•
•
•
•
•
•
The eye is basically similar to a camera.
It has a lens to focus light onto the Retina of eye.
Retina full of neurons.
neurons.
Each neuron is either a rod or a cone.
Rods are not sensitive to color.
Cones come in 3 types: red, green and blue. Each responds
differently to various frequencies of light.
Color Depth
• 4 bit 24 16 grey levels
0000, 0001,0010, 0100, 1000 …,
…, dst.
8 bit 28 256 aras keabuan
Color Depth
• 1bit color (21=2 colors) monochrome, often black and white
• 2bit color (2²=4 colors) CGA, gray-scale early NeXTstation
• 3bit color (2³=8 colors) Many early home computers with TV
out displays
• 4bit color (24=16 colors) as used by EGA and by the least
common denominator VGA standard at higher resolution
• 5bit color (25=32 colors) Original Amiga chipset
• 6bit color (26=64 colors) Original Amiga chipset
• 8bit color (28=256 colors) Most early color Unix
workstations, VGA at low resolution, Super VGA, AGA
• 12bit color (212=4096 colors) some Silicon Graphics systems,
Color NeXTstation systems, and Amiga systems in HAM mode.
• 24bit color true color
• 32bit color true color
• 64bit color LCD
Color Depth
2 bit
8 bit
4 bit
24 bit true color
Color Model
Additive (RGB)
Subtractive (CMYK)
Having fun with...
Multimedia
HW
• 1. Find how many colors are visible?
• 2. In color image with 8 bits per pixel, how
is the representation?