Transcript 计算机交叉学科

MULTIMEDIA TECHNOLOGY
AND APPLICATIONS
CHAPTER 3. GRAPHICS & IMAGE
PROCESSING
LIGHT
Light: electromagnetic radiation of a wavelength
that is visible to the human eye.
 Visible Spectrum: 380/400 nm ～ 760/780 nm).

COLOR
Color：the visual perceptual property corresponding
in humans to the categories called red, green, blue
and others.
 Derives from the spectrum of light interacting in the
eye with the spectral sensitivities of the light
receptors.

wavelength
interval
frequency
interval
red
~ 700–635 nm
~ 430–480 THz
orange
~ 635–590 nm
~ 480–510 THz
yellow
~ 590–560 nm
~ 510–540 THz
green
~ 560–490 nm
~ 540–610 THz
blue
~ 490–450 nm
~ 610–670 THz
violet
~ 450–400 nm
~ 670–750 THz
color
COLOR





Color in human vision: Hue,
Saturation, and Lightness.
Hue: the property of colors
by which they can be
perceived as ranging from
red through yellow, green,
and blue.
Saturation: the colorfulness of a color relative to its
own brightness, (the amount of white light).
Hue + Saturation = Chroma
Brightness: reflects the subjective brightness
perception of a color for humans along a lightness–
darkness axis.
COLOR
Color Model: an abstract mathematical model
describing the way colors can be represented as
three or four values or color components.
 RGB Model: an additive color model in which red,
green, and blue light are added together in
various ways to reproduce a broad array of colors.

Red (R):
Green (G):
Blue (B):
0~255
0~255
0~255
COLOR
CMYK Model: a subtractive color model, used in
color printing.
 CMYK refers to the four inks used in some color
printing: cyan, magenta, yellow, and key black
Cyan (C): 0-100%
Magenta (M): 0-100%
Yellow (Y): 0-100%
Black (K): 0-100%

C=M=Y=K=0% White
C=M=Y=K=100% Black
COLOR
RGB & CMYK
 R＝Y＋M
 G＝C＋Y
 B＝C＋M
 K＝C＋M＋Y
 W＝R＋G＋B
 C＝W－R
 M＝W－G
 Y＝W－B
COLOR


HSL/HSB: stands for hue,
saturation, and
lightness/brightness.
Based more upon how colors
are organized and
conceptualized in human
vision.
COLOR
YIQ/YUV: Color models used by TV systems.
 YIQ: NTSC color TV system (mainly in North
and Central America, and Japan).
 YUV: PAL, SECAM color TV systems (China,
France)
 Y represents the luma information.
 IQ/UV represent the chrominance information.
 UV = X and Y coordinates within the color space.
 IQ = a second pair of axes on the same graph,
rotated 33°.

COLOR


Grayscale: describes the colors ranging from black to
white. (8 bits for each pixel, 28=256 levels)
Black-and-White (monochrome): 1 bit for each pixel
Color
Greyscale
Black-and-White
GRAPHICS & IMAGE
Graphics (Vector Graphics): the use of geometrical
primitives such as points, lines, curves, and shapes or
polygon(s), which are all based on mathematical
equations, to represent images in computer graphics.
 Example: Circle = (location of centre point, radius,
color).
 Strength: storage space requirement
 Drawback: processing time
 Software: CorelDRAW, FreeHand

GRAPHICS & IMAGE
Image (Bitmap): Bitmap-based images are
comprised of pixels in a grid. Each pixel or "bit"
in the image contains information about the
color/brightness to be displayed.
 Discretization of space and brightness.
 Strength: abundant of colors, realistic
 Drawback: loss quality when resizing, big storage
spare
 Software: Photoshop
PhotoImpact

GRAPHICS & IMAGE

Vector Graphics vs. Bitmap Image
Vector
Bitmap
• scalable
• resolution independent
• no background
• cartoon-like
• inappropriate for realistic images
• metafiles contain both raster and
vector data
• pixels in a grid
• resolution dependent
• resizing reduces quality
• easily converted
• restricted to rectangle
• minimal support for transparency
Photorealistic Rendering
Vector
Pattern Recognition
Bitmap
IMAGE DIGITALIZATION

The discretization and digitalizaiton of the
continuous spatial position and brightness values.
Spatial
space
sampling
m×n
20×13
Brightness
quantization
256
8b
24b
IMAGE CHARACTERISTICS

Resolution: a measurement of the output quality of an image,
usually in terms of samples, pixels, dots, or lines per inch.
Display Resolution: the number of distinct pixels in each
dimension that can be displayed on digital device. (640*480,
800*600, 1024*768)
 Image Resolution: the actual number of pixels contained in the
digital image, it decides the displaying size of the image on the
display device.
 Pixel Resolution: the aspect ratio of displaying a pixels.
Different pixel resolutions between the transferring
devices would cause image distortion.

IMAGE CHARACTERISTICS

Color Depth: the number of bits used to
represent the color of a single pixel in a
bitmapped image or video frame buffer.

Color Image: the maximum number of colors

Grayscale Image: the maximum number of
brightness
1-bit (21): monochrome, often black and
white.
2-bit (22): CGA, gray-scale.
4-bit (24):EGA and the least common
denominator VGA standard at higher resolution,
color Macintoshes, Windows 3.x.
8-bit (28 = 256): most early color Unix
workstations, VGA at low resolution, Super
VGA, AGA, color Macintoshes.
16-bit (216 = 65536): some color Macintoshes
COLOR DEPTH

24-bit truecolor uses 8:8:8 bits to represent
R:G:B, respectively. 16,777,216 mixed colors
(256 × 256 × 256).

32-bit color is generally a misnomer in regard
to display color depth. While actual 32-bit color
at ten to eleven bits per channel produces over
4.2 billion distinct colors.

Sometimes refers to 24-bit color images with an additional
eight bits of non-color data (I.E.: alpha, Z or bump data).
IMAGE CHARACTERISTICS

Storage Requirement:
Storage ＝Resolution×Color Depth/8 (Byte)
A 640×480 bitmap image requires
640×480×24/8＝921600B＝900KB of storage.
IMAGE CHARACTERISTICS

Image Quality Assessment



Full-reference (FR): the quality of a test image is
evaluated by comparing it with a reference image
that is assumed to have perfect quality.
No-reference (NR): assess the quality of an image
without any reference to the original one.
Image Quality Factors







Sharpness
Noise
Dynamic Range
Contrast
Distortion
Exposure Accuracy.
Etc.
IMAGE FILE FORMAT
Image file formats are standardized means of
organizing and storing digital images. Image files
are composed of either pixel or vector (geometric)
data that are rasterized to pixels when displayed
(with few exceptions) in a vector graphic display.
 BMP (Bitmap): standard bitmap digital images,
especially on Microsoft Windows and OS/2.

Each file stores only one image
 Image pixels are stored with a color depth of 1, 4, 8,
16, 24, or 32 bits per pixel.
 Uncompressed bitmap files are typically much larger
than compressed versions.

IMAGE FILE FORMAT
JPEG (Joing Photographic Experts Group): The most
important current standard for image
compression.
 The human vision system has some specific
limitations and JPEG takes advantage of these to
achieve high rates of compression.
 JPEG allows the user to set a desired level of
quality, or compression ratio (input divided by
output).

IMAGE FILE FORMAT






GIF (Graphics Interchange Format): format commonly used
to display indexed-color graphics and images in HTML
documents over the internet and other online services.
LZW-compressed.
GIF format preserves transparency in indexed-color
images; however, it does not support alpha channels.
Limited to 8-bit (256) color images only.
GIF standard supports interlacing --- successive display
of pixels in widely-spaced rows by a 4-pass display process.
GIF actually comes in two flavors:
GIF87a: The original specification.
 GIF89a: The later version. Supports simple animation via a
Graphics Control Extension block in the data, provides simple
control over delay time, a transparency index, etc.

IMAGE FILE FORMAT
PNG (Portable Network Graphics) meant to
supersede the GIF standard, and extends it in
important ways.
 Special features of PNG les include:

Support for up to 48 bits of color information --- a
large increase.
 Files may contain gamma-correction information for
correct display of color images, as well as alphachannel in formation for such uses as control of
transparency.
 The display progressively displays pixels in a 2dimensional fashion by showing a few pixels at a
time over seven passes through each 8 8 block of an
image.

IMAGE FILE FORMAT

TIFF (Tagged Image File Format): The
support for attachment of additional information
(referred to as “tags”) provides a great deal of
flexibility.
The most important tag is a format signifier: what
type of compression etc. is in use in the stored image.
 TIFF can store many different types of image: 1-bit,
grayscale, 8-bit color, 24-bit RGB, etc.
 TIFF was originally a lossless format but now a new
JPEG tag allows one to opt for JPEG compression.
 The TIFF format was developed by the Aldus
Corporation in the 1980's and was later supported by
Microsoft.

IMAGE FILE FORMAT



PSD (Photoshop format): the default file format
supports all Photoshop features. Because of the
tight integration between Adobe products
Maintains the appearance of the document, just
in case future versions of Photoshop change the
behavior of some features.
16-bits-per-channel and high dynamic range
32-bits-per-channel images can be saved as PSD
files.
IMAGE FILE FORMAT

Vector Image

EPS (Encapsulated PostScript)

DXF (AutoCAD file format)

CDR (CorelDRAW file format)

WMF / EMF (Windows Metafile / Enhanced Metafile)
IMAGE COMPRESSION

Compression: the process of coding that will
effectively reduce the total number of bits needed
to represent certain information.
1st Generation: Information Theory (e.g., Predictive
coding, Transforming coding)
 2nd Generation: Subjective Factors (e.g. Subband
coding)
 3rd Generation: International Standard
(ISO/IEC/ITU-T：JPEG、MPEG、H.261)

IMAGE COMPRESSION
Necessity of compression: Redundancy and
Relevancy
 Compression Techniques

Lossless
Reversible
Huffman coding
Run-length coding
Arithmetic coding
etc.
Lossy
Irreversible
Predictive coding
Transforming coding
Subband coding
Wavelet-based coding
etc.
JPEG COMPRESSION STANDARD
JPEG is a lossy image compression standard that
was developed by the “Joint Photographic
Experts Group".
 JPEG was formally accepted as an international
standard in 1992.
 Employs a transform coding method using the
DCT (Discrete Cosine Transform).

Original
Image
DCT
Quantization
Quantization Tables
Reconstructed
Image
Inverse DCT
Re-Quantization
Coding
Coding Tables
Decoding
Image
Compression
JPEG COMPRESSION STANDARD

JEPG2000 created by the Joint Photographic
Experts Group committee in 2000 with the
intention of superseding JPEG with a newly
designed, wavelet-based method








Superior compression performance
Multiple resolution representation
Progressive transmission
Lossless and lossy compression
Random code-stream access and processing
Error resilience
Flexible file format
Side channel spatial information.
JPEG COMPRESSION STANDARD

JPEG vs. JPEG2000
Standard
Date
Compression
Ratio
Techniques
Applications
JPEG
JPEG 2000
1986.3-1992.10
1996.2-2000.12
2-30:1
2-50:1(improved 30-50%)
Discrete Cosine Transform Discrete Wavelet Transform
Huffman Coding
Embedded Block Coding with
Arithmetic Coding
Optimal Truncation
Region of Interest
Internet
Digital Cameras
Video Imaging
Internet
Digital cameras
Printers
Scanners
Mobile phones
IMAGE PROCESSING SOFTWARE
Adobe Photoshop: graphics editing
program developed and published by Adobe
Systems
 1978, “Display” by Thomas Knoll & John Knoll

John Knoll

Thomas Knoll
1990, Adobe released Photoshop 1.0
PHOTOSHOP
Photoshop Release History
1.0
2.0
2.5
3.0
5.0
Feb 1990
Jun1991
1993
Sep 1994
May 1998
5.5
6.0
7.0
Feb1999
Sep 2000
Mar 2002
Color correction with Balance, Hue, and Saturation, Curves, etc.
Paths; Rasterizer for Adobe Illustrator® files; Support for CMYK color, etc.
Palettes, Support for 16-bit files, etc.
Layers; Tabbed Palettes, etc.
ICC-based color workflows, Multiple Undo, Magnetic Lasso, Editable Type, etc
ImageReady, Save for Web; Extract; Image slicing and rollover effects, etc
Vector Shapes, Updated user interface, Liquify filter, etc
Healing Brush, New painting engine, Photoshop file browser,etc
Shadow/Highlight command, Match Color command, Lens Blur filter, Real-Time
CS (8.0)
Oct 2003
Histogram, Highly modified Slice tool, Hierarchical Layer groups
Adobe Bridge 1.0, Smart Objects, Image Warp, Spot Healing brush, Red-Eye
CS2 (9.0) Apr 2005
tool, Lens Correction filter, Smart Sharpen, etc.
Smart Filters, Native Intel Macintosh support, Quick Selection tool, 3D
CS3 (10.0) Apr2007
visualization and texture editing, MATLAB integration, etc.
Adjustments panel, Masks panel, Breakthrough 3D editing and compositing,
CS4 (11.0) Sep 2008
Enhanced motion graphics, Volume Rendering, etc.
Content-Aware Fill, HDR Pro and HDR Toning, Easy 3D extrusions with Adobe
CS5 (12.0) May 2010
Repoussé, Rich 3D materials library, Motion-based content editing, etc.
PHOTOSHOP
©Some of the pictures and text are from internet online free resource and wikipedia