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.

colorwavelength

intervalfrequency 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 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): 0~255Green (G): 0~255Blue (B): 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% WhiteC=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

Vector Bitmap

Photorealistic Rendering

Pattern Recognition

IMAGE DIGITALIZATION

The discretization and digitalizaiton of the continuous spatial position and brightness values.

Spatial Spatial space space

samplinsamplingg

m×nm×n

2020×13×13

256256

Brightness Brightness quantizatiquantizati

onon

8b8b

2424bb

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 alpha-channel in formation for such uses as control of transparency.

The display progressively displays pixels in a 2-dimensional 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

LosslessReversible

Huffman codingRun-length codingArithmetic codingetc.

LossyIrreversible

Predictive codingTransforming codingSubband codingWavelet-based codingetc.

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

Reconstructed Image

Inverse DCT

DCT Quantization

Re-Quantization

Coding

Decoding

Image Compression

Quantization Tables Coding Tables

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. 

Standard JPEG JPEG 2000

Date 1986.3-1992.10 1996.2-2000.12

Compression Ratio

2-30:1 2-50:1(improved 30-50%)

Techniques

Discrete Cosine TransformHuffman CodingArithmetic Coding

Discrete Wavelet TransformEmbedded Block Coding with Optimal TruncationRegion of Interest

Applications

InternetDigital CamerasVideo Imaging

InternetDigital camerasPrintersScannersMobile phones

JPEG COMPRESSION STANDARD

JPEG vs. JPEG2000

IMAGE PROCESSING SOFTWARE

Adobe Photoshop: graphics editing program developed and published by Adobe Systems

1978, “Display” by Thomas Knoll & John Knoll

1990, Adobe released Photoshop 1.0

Thomas KnollJohn Knoll

PHOTOSHOP

Photoshop Release History

PHOTOSHOP

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