程序代写代做代考 GPU PowerPoint Presentation

PowerPoint Presentation

Images and Displays

Computer Graphics
Instructor: Sungkil Lee

Today

• Digital Images

• Raster Graphics

• Vector Graphics

• Displays

Images

• Image:

• (continuous) 2D distribution of intensity or color, defined as a 2-D
function 𝑓 𝑥, 𝑦 at spatial coordinates (𝑥, 𝑦)

• 𝑓 𝑥, 𝑦 is the intensity (or gray level) or the amplitude of light.

Lena: the most famous test image in image processing community

Digital Images

• Digital image: a finite, discrete quantities of image

• finite range: e.g., 0-255

• discrete quantities: e.g., 0, 1, 2, …., 255 (integer only here)

• usually has 3 channels: RGB (red, green, and blue)

• motivated by 3 types of cone cells (L, M, S) in the retina

• Pixel (picture element):

• A single element of a digital image

• For multi-channel images, three channel elements form a pixel.

• c.f., voxel (volume element), texel (texture element)

Digital Images: Example

• 3-channel RGB format

• Intensity of the red channel is stronger than the other two in the example.

red green blue RGB+ + =

Raster Graphics

• A raster graphics representation (also called the bitmap)

• 2D array structure that represents a rectangular grid of pixels.

• When enlarged, a blocky structure is visible

Raster Graphics

• Memory structure

• e.g., BGR format in Windows BMP

B G R B G R B G R

…

B G R B G R B G R

B G R

B G R…

…

width × 3

h
e
ig

h
t

unsigned char image[height*width*3]; // as a 1D array

Raster Graphics

• Implication of a raster image

• approximation (sampled representation) of a real intensity distribution

• c.f., a float-point number in computer is always an approximation.

• A single pixel represents the color of the pixel center, not on the whole
area of a pixel.

• example: the yellow color of the center approximates the whole pixel area.

• Advantages:

• Brute-force sampling can represent arbitrary images; memory is cheap.

• Quality becomes higher with increasing resolution (denser sampling)

• 2D array can easily be mapped to display devices.

Raster Graphics: Data Types

• Bitmaps:

• boolean per pixel (black or white); e.g., fax, (old) newspaper

• Grayscale:

• integer per pixel (gray levels)

• Precision: usually 8-bits per pixel (bpp), but often 10, 12, 16 bpp

• Color:

• 3 or 4 integers per pixel (RGBA for 4 integers)

• “A” means “alpha” or opacity

• Precision: usually 24 bpp (RGB) or 32 bpp (RGBA)

• Floating-point

• Floating-point format is often used for high-dynamic range (48 or 96 bpp)

• Exposure effects can be captured with HDR formats

Raster Graphics: Storage Requirements

• 1024 × 1024 image (1 Megapixel) example

• bitmap: 128 KB

• grayscale 8bpp: 1MB

• grayscale 16bpp: 2MB

• color 24bpp: 3MB

• floating-point HDR color: 12MB

• Think about:

• how many memory is required for an arbitrary resolution and bpp.

Raster Graphics: File Containers

• Compression of image files

• When images are stored into disks with particular formats, they are
usually compressed. So, you see much smaller file sizes for them.

• Typical containers

• BMP: Lossless raw format

• JPEG: Lossy compression (pronounced as “Jay-Peg”)

• Using DCT (discrete cosine transform for compression)

• PNG: Lossless compression (pronounced as “Ping”)

• Using ZLIB for compression

• TIFF, GIF, … (obsolete)

• WebP (recent container/compression by Google)

Vector Graphics

• Unlike the raster graphics, vector graphics uses geometrical
primitives such as points, lines, triangles, curves, etc.

• The primitives are represented as a mathematical expressions.

• “Vector”, in this context, is more than a straight line.

• Common tools/formats to manipulate 2D vector graphics

• Adobe illustrator

• Adobe Acrobat

• SVG (Scale Vector Graphics; recently available on the web)

• Postscripts (for printers or printer file)

Vector Graphics

• Vector graphics representations are usually independent of
the output resolution.

• Because they are rasterized on the fly at the output stage to be displayed.

• Still, most of display devices use raster display.

3D Graphics and Images

Vector Graphics to Raster Graphics

• Input: vector representation

• Graphics uses vector graphic formats as an input

• Points, lines, triangles, quads, polygons, curves, …

• Output: raster representation

• Raster images whose dimension is identical to the window resolution

Graphics Terms

• “capture images” means:

• record the light distribution on the sensor (using cameras)

• “represent images” means:

• encode images numerically (normally binary)

• “display images” means:

• realize the encoded images as actual intensity distribution on the display
devices (e.g., monitors)

Displays

Raster Display System

• Screen image is defined by a 2D array in RAM

• The memory area is called the frame buffer.

• Nowadays, the most system has it in Graphics Processor Unit (GPU)
memory.

• Architecture of raster display system

CPU GPU
Main

memory

System Bus

I/O Devices

GPU

Memory

Frame

Buffer

Video

Controller
Monitor

Display Devices

• Computer displays

• CRT (Cathode Ray Tube)

• LCD (Liquid Crystal Display)/LED (Light Emitting Diode)

• OLED (Organic LED)

• AMOLED (Active Matrix OLED)

• Printers

• Laser printers

• Inkjet printers

• Dot printers (-1990s)

• not much of interests in this course

Cathode Ray Tube (CRT)

• Raster scan display

• Can be used either as vector (calligraphic or random-scan) display device
or raster display system (from frame buffer)

• TV-standards: PAL, NTSC

• Direct view storage tube (DVST):

• an early alternative for persistent display without constant refresh

y deflect

x deflectElectron gun

Focus

Phosphor

LCD Flat Panel (TN: Twisted Nematic)

• Principle:

• Block or transmit light by twisting its polarization

• Intermediate intensity levels possible by partial twist

• Fundamentally raster technology

• Always need backlight (often using LED)

LCD Flat Panel (IPS: In-plane Switching)

• Principle:

• While TN panel twists LC vertically, IPS panel twists
LC horizontally in its plane.

• Better for wide-angle viewing.

OLED (Organic Light Emitting Diode)

• Principle:

• Self-emit or not light by organic materials

• Works without backlit: better in contrast ratio than LCD

• Fundamentally raster technology

1. Cathode (−), 2. Emissive Layer, 3. Emission of radiation, 4. Conductive Layer, 5. Anode (+)

AMOLED (Active-Matrix OLED)

• Principle:

• Active matrix addressing:

• Each element’s state is maintained by individual circuits.

• Faster than passive matrix addressing in refresh rates

※ Super AMOLED (Samsung Elec. Co. Ltd.) = AMOLED + touch digitizer

Pentile matrix pattern on Galaxy S6/S7

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