1. Scanners

2. Learning Objectives Understand what the TWAIN standard is/
Understand how TWAIN drivers interface with hardware and applications.
Understand how a scanner is constructed.
Understand how a scanner captures an image.
Understand the different types of flat bed scanners.

3. TWAIN
TWAIN is a standard which specifies how image acquisition device such as scanners and digital cameras transfer data to applications
TWAIN allows applications to work with image acquisition devices without knowing anything about the device itself.

4. TWAIN (cont)
If a image acquisition device and an application are TWAIN compliment they should work together.
When you purchase an image acquiring device such as a digital camera or a scanner in comes with TWAIN drivers.

5. TWAIN (cont)
This makes it possible for TWAIN compliant applications to access different hardware devices.
In software applications that are TWAIN compliant the Select Source option on the File menu is used to select the device.

6. TWAIN (cont)
When you select the specific device the TWAIN drivers for that device are launched
A screen will appear that allow you to control the device and access the images you want to transfer.

7. TWAIN (cont)
When you complete any image processing such as scanning, the image is transferred to the application.

8. Imaging Software
TWAIN
Module
Scanner
TWAIN
Module
Digital
Camera

9. Imaging Software
TWAIN
Module
Scanner
TWAIN
Module
Digital
Camera

10. TWAIN (cont) The letters in acronym TWAIN have no real meaning.
Kevin Bier the chairman of the original TWAIN standards group was aggravated by all of the suggestions for a name for the technology

11. TWAIN (cont)
Kevin made up the name TWAIN and said it meant “toolkit without an important name”

12. Scanners
Light-sensing device that reads printed text and graphics and converts them into digital information

13. Scanners (cont.) There are four basic types of scanners; Sheet-fed
Flatbed
Pen or Handheld
Drum

14. Scanner How it works Step 1
Document to be scanned is placed face down on the glass window

15. Scanner How it works Step 2
Bright light moves underneath scanned document.

16. Light Source (lamp) A lamp is used to illuminate the document.
The light source can be either a
Cold Cathode Fluorescent Lamp (CCFL)
xenon lamp

17. Scanner How it works Step 3
Image of the document is reflected into a series of mirrors and into a lens.

18. Scanner How it works Step 4
The lens focus the light on to a CCD device.

19. Scan Head
The mirrors, lens, filter and CCD array make up the scan head.

20. Scanner How it works Step 5
Light is converted to analog electrical current in the CCD device.

21. CCD The core component of the scanner is the CCD array
CCD is a collection of tiny light-sensitive diodes, which convert photons (light) into electrons (electrical charge).

22. Scanner How it works Step 6
The analog information is sent to a ADC where it is converted to digital information. The digital information is transferred to the PC through a USB cable.

23. Step Motor
The scan head is moved slowly across the document by a belt that is attached to a stepper motor

24. Stabilizer Bar
The scan head is attached to a stabilizer bar to ensure that there is no wobble or deviation in the pass.

25. Scanners (cont) The resolution of a scanner is determined by;
The number of sensors in a single row (x-direction sampling rate) of the CCD or CIS array
the precision of the stepper motor (y-direction sampling rate).

26. Scanners (cont) The CanoScan 8400F has optical: 3200 dpi
hardware: 3200 x 6400 dpi
Interpolated: 19,200 x 19,200 dpi

27. Scanners (cont)
Interpolation is a process that the scanning software uses to increase the perceived resolution of an image.
It does this by creating extra pixels in between the ones actually scanned by the CCD array

28. Scanners (cont)
These extra pixels are an average of the adjacent pixels.
Interpolation creates slightly soft focused results.

29. Scanners (cont)
Another imaging array technology that has become popular in inexpensive flatbed scanners is contact image sensor (CIS).
CIS replaces the CCD array, mirrors, filters, lamp and lens with rows of red, green and blue light emitting diodes (LEDs).

30. Scanners (cont)
When the image is scanned, the LEDs combine to provide white light.
The illuminated image is then captured by the row of sensors.
CIS scanners are cheaper, lighter and thinner, but do not provide the same level of quality and resolution found in most CCD scanners.