Data Translation, Inc.
Download
1 / 63

Imaging-Concepts - PowerPoint PPT Presentation


  • 97 Views
  • Uploaded on

Data Translation, Inc. Basics of Image Processing. Types of Video Images. Monochrome Image made up of varying shades of gray, from black to white Number of shades depends on resolution of frame grabber. Monochrome Resolutions. Types of Video Images. RGB Color –

loader
I am the owner, or an agent authorized to act on behalf of the owner, of the copyrighted work described.
capcha
Download Presentation

PowerPoint Slideshow about 'Imaging-Concepts' - Lucy


An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.


- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -
Presentation Transcript

Data Translation, Inc.

Basics of Image Processing


Types of video images
Types of Video Images

  • Monochrome

    • Image made up of varying shades of gray, from black to white

    • Number of shades depends on resolution of frame grabber



Types of video images1
Types of Video Images

  • RGB Color –

    • Three sets of brightness signals

    • One for each: RED, GREEN, BLUE


Capturing images
Capturing Images

  • Terminology

    • Video formats

    • Frames (interlaced and non-interlaced)

    • Fields (odd and even)

    • Video signals


Standard video fundamentals
Standard Video Fundamentals

  • Light collides with the surface of an image sensing device (camera)

  • Result: an electrical voltage level, related to the amount of light hitting the particular area of the surface, is produced


Video format
Video Format

  • This information is then arranged into a standard format and output from the camera

  • Sync pulses are also added so that the receiving device can recognize where the sequence is in the frame data


Simplified camera diagram
Simplified Camera Diagram

Lens

Target

Object

Electron Beam

Video Signal


Pixels
Pixels

  • Images are broken down into horizontal lines

  • Lines are broken down into picture elements, or pixels


Monochrome pixels
Monochrome Pixels

Each pixel has a gray value. On 8-bit systems, 0=black and 255=white. All other values are shades of gray.


Color pixels
Color Pixels

Each pixel contains 3 colored phosphors: RED, GREEN, and BLUE. Each color receives a different intensity value (similar to “gray scale” in monochrome image processing). The resulting combinations determine which color we see.


Frames
Frames

  • Interlaced

  • Non-interlaced


Interlaced image frames
Interlaced Image Frames

  • All odd-numbered lines are read from top to bottom, followed by all even-numbered lines


Interlaced image frames1
Interlaced Image Frames

  • - Diagonal lines are active video

  • Horizontal lines are blanking (beam off)

  • - At the bottom of the raster, the beam if off and video begins its vertical retrace (vertical blanking)


Fields
Fields

  • Interlacing causes the frame to be divided into two fields: odd and even

  • Each field is displayed sequentially giving the perception that the frame is updated twice as often as it really is


Fields1
Fields

  • Each field updated every 1/60 or 1/50 s

  • Each frame updated every 1/30 or

    1/25 s

  • 60 (50) fields per second: 30 (25) odd and 30 (25) even


Fields2
Fields

  • This method reduces noticeable flicker when displaying images

  • When working with graphics or thin lines, flicker becomes extremely noticeable


Fields3
Fields

  • To reduce flicker:

    • Use horizontal lines that are wider than 1 pixel (2 lines??)

    • Use long-persistence monitor

    • Use non-interlaced monitor for graphics


Monitors
Monitors

  • An electron beam scans the surface of the display tube

  • A horizontal sync resets the beam to the left-most side of the screen and then moves it down to the next line

  • When a vertical sync is detected, the beam is reset to the top, left-most point of the screen


Diagram of monitor essentials
Diagram of Monitor Essentials

Phosphors

Video Signal

Gun

Grid

Electrons


Video signals
Video Signals

  • A video signal contains a series of analog TV lines

  • Lines are separated from one another by a sync pulse called horizontal sync

  • Fields are separated by a longer sync pulse called vertical sync


Typical video line
Typical Video Line

Blanking Level

Active Pixel Region

Horiz. Sync

Horiz. Blanking

Full Scan Area


Video signals1
Video Signals

  • Digital video transfers several bits (representing pixel values) simultaneously

  • Two voltage levels, Logic 0 and 1

  • Transmitted on individual TTL (Transistor-Transistor Logic) lines or pairs of lines in differential mode (RS-422 standard, less noise)


Interfacing input devices with frame grabbers
Interfacing Input Devices with Frame Grabbers

  • Video Formats:

    • RS-170 and CCIR

    • RS-170 RGB and CCIR RGB

    • NTSC and PAL


Rs 170
RS-170

  • Specifies all timing and voltage levels for standard commercial video signals

  • Used as basis for most B&W video equipment in the U.S.


Rs 1701
RS-170

  • For 60 Hz television systems (North American standard)

  • Frame consists of 525 lines and is displayed once every 1/30 of a second

  • Each field contains 262.5 lines


Rs 1702
RS-170

  • Each field also contains 9 sync lines (18 lines per frame) and 11 “no video” or “blanking” lines

  • A video frame consists of 485 viewable lines:

    525 – 18 (sync) – 22 (blanking) = 485


Rs 1703
RS-170

  • For camera compatibility, most frame grabber manufacturers design boards which capture 480 lines

  • Therefore, lines are clipped at the top and bottom of the image


Rs 170 rgb
RS-170 RGB

  • Three RS-170 type signals, one for each of the additive primary colors – red, green, and blue

  • Red, green and blue images are displayed simultaneously

  • Image manipulations must be performed independently on all three components


CCIR

  • CCIR – International Radio Consultative Committee

  • 50 Hz equivalent to RS-170

  • A frame consists of 625 lines

  • Subtracting sync and blanking lines yields 544 lines of displayable video

  • Lines are clipped from top and bottom to display 512 lines


NTSC

  • NTSC – National Television Standards Committee

  • Standard specification for color signals – 60 Hz

  • Single line input

  • Color is superimposed over the monochrome (RS-170) signal


NTSC

  • Color can be removed by frame grabber using chrominance filter

  • Three most popular NTSC uses:

    • Broadcast television

    • Cable television

    • VCRs


Pal phase alternation line
PAL (Phase Alternation Line)

  • 50 Hz equivalent to NTSC

  • European standard


Summary of standard signals
Summary of Standard Signals

*USA = US, Canada, Japan, Brazil INTL = Most other countries


Non standard video signals
Non-standard Video Signals

  • Input device tells frame grabber when to digitize

  • Non-interlaced signal

  • All lines are read in succession to create a frame

  • One type is referred to as “slow scan”


Non standard video signals1
Non-standard Video Signals

  • The following control signals must be provided by the user

    • Scan trigger

    • Clock enable

    • Pixel clock

    • Pixel value (analog)



Picture aspect ratio
Picture Aspect Ratio

  • The relationship between the width and height of a frame

4

3


Pixel aspect ratio
Pixel Aspect Ratio

  • The relationship between the width and height of a pixel

US

5:4

1:1

INTL

3:2

1:1


Chrominance filter
Chrominance Filter

  • Jumper-selectable circuit that removes color information from NTSC signals. Normally found on monochrome frame grabbers to prevent interference with the monochrome image

  • Implemented via a notch filter


Look up tables lut s
Look-Up Tables (LUT’s)

  • Implements pixel (point) processing

  • One value goes in, another comes out

0 = 0

60 = 75

75 = 19

193 = 200

222 = 222

230 = 229

75

19


Input look up tables
Input Look-Up Tables

  • Used for thresholding

  • Real-time processing

  • Add or multiply by a constant


Thresholding
Thresholding

  • A pixel operation used to reduce the number of gray levels displayed

  • One example is binary thresholding, resulting in either black or white


Binary thresholding example
Binary Thresholding Example

0 - 160

0

LUT

161 - 255

255


Binary thresholding example 2
Binary Thresholding Example #2

0 - 80

0

81 - 175

100

LUT

176 - 225

200

226 - 255

0


Contrast
Contrast

  • Refers to the clarity (sharpness or dullness) of an image

  • A result of the ratio of black to gray to white


Histogram
Histogram

  • Graphic representation of contrast

Number of pixels

50

40

30

0 = black, 255 = white

20

10

0 20 40 60 80 100 120 140 160 180 200 220 240 255


Histogram equalization
Histogram Equalization

  • Alters the histogram, thereby smoothing the contrast


Zoom

  • Magnification of an image

  • Typical factors: 2, 4, or 8


Pan

  • Shifts image to left or right


Scroll
Scroll

  • Shifts image up or down


Overlay
Overlay

  • Graphics or text that can be added to an image

  • Destructive and non-destructive


Area of interest aoi
Area of Interest (AOI)

  • Also known as Region of Interest (ROI) or Active Region of Interest

  • A portion of an image

  • Specific rows and columns form a rectangular section to be worked on


Frame buffer
Frame Buffer

  • An individual array of image data. Most common are:

    • 512 x 512 x 8 bits (256 Kb of memory) used on older boards

    • 640 x 480 x 8 bits (300 Kb of memory) used on newer boards


Filtering
Filtering

  • A method of massaging the image’s data


Types of filtering
Types of Filtering

  • Low pass – blur

  • High pass – sharpen

  • Laplacian – enhance all edges

  • Horizontal edge detection/enhancement

  • Vertical edge detection/enhancement


Group processing
Group Processing

  • Works on a group of pixels at one time

  • Used for filtering


Kernel
Kernel

  • Arithmetic grid used to perform filtering

16

Original Pixel Values

Kernel

Resulting Middle Pixel


Frame averaging
Frame Averaging

  • Adds together several frames, then divides by the number of frames. This produces a less noisy image

  • True vs. Weighted


Logic operations
Logic Operations

  • Provide a pixel-by-pixel combination of two images


Logic operations1

0

1

0

0

0

1

1

0

Logic Operations

O = False

1 = True

AND

OR

XOR

0

1

0

1

0

0

1

0

0

1

1

1

1

0

1

1


Hue saturation intensity hsi
Hue Saturation Intensity (HSI)

  • “Human view of colors”

  • Rather than specifying a color as percentages of red, green and blue, they are specified as “dark magenta” or “light aqua”

  • Takes the same number of bits to store an HSI image as an RGB one


Conclusion
Conclusion

Additional image processing questions? Contact Data Translation at

(800) 525-8528


ad