Input and output devices Flashcards
How do 2D scanners work?
- Place the device on the glass plate and close the cover.
- Bright light (fluorescent lamp, CCFL, xenon lamps - order of previously used to modern) illuminates the document.
- Scan head moves across the document until the whole page has been scanned.
- Image of the document is produced, which undergoes a series of reflection on mirrors, and is sent to a lens. Lens focuses the image onto the CCD.
- Charged coupled device (CCD) consists of thousands of light-sensitive elements or pixels. Each pixel creates an electric charge when light falls on it. This way, the document is turned into an electronic form and sent to the computer.
Where are 2D scanners applied?
- flatbead scanners for scanning documents
- scanners used at airports to read passports -
Scanner technology is used to read passports.
OCR is used for converting the content to digital files (e.g. ASCII for text and JPEG for images).
By doing so, the information can be manipulated in different ways, for example, it can be saved in the database of records of passengers.
Image of the person is taken, at many airports, using a digital camera. This image is compared to the one in the passport for authentication.
Key parts of the face are given coordinates by the software - both on the passport image and the new image - and the distances are mapped onto each other. If they match, the software determines that it is the same person.
Example distances could be the distance between eyes, shape of the brows, width of the nose, facial width, etc.
How do 3D scanners work?
Laser scanners:
- Object is placed on a turner.
- Laser light rays are shot at the object to figure out its size and shape (depending on how long the rays took to reach the object).
- A 3D model of the object is constructed on a software (eg. AutoDesk).
Light scanners:
- Object is placed on a turner in a well-lit room.
- Several images of the objects are taken at different angles as it is turning.
- These images are all assembled using a software to construct a 3D image of the object.
Where are 3D scanners applied?
- 3D models in the software are used for printing objects (using 3D printers).
- CT scanners - a person is sent through a tunnel equipped with a X-Ray sender and a receiver opposite it. X-Rays are sent through the person’s body and sent to a software, which forms a 3D image of the person’s cross section.
- MRI scans
- SPECT scans
What is barcode?
A series of parallel black bars of varying width printed on objects, that contains information about them.
What are barcode readers?
Scanners that read barcode.
How do barcode readers work?
- Use a barcode scanner to read the barcode. Red laser beam or LED is emitted.
The light is reflected off the products. It can be read since the dark areas reflect no light.
- Sensors are used for determining if an area is dark or light.
- The pattern generated by the sensors (eg. A B B B A A A; where A is light and B is dark) can be used for creating a corresponding binary code (eg. 1001000).
- The binary number generated is the key field in the stock item record in the database that uniquely identifies each item.
- Information (eg. price) about the item is sent to the checkout.
Where are barcode readers applied?
- They are used at supermarkets to facilitate buying of products.
- They are used in airports, to scan boarding tickets of passengers.
- They are used in libraries to keep track of the procedures.
(They are also inspiration for art and architecture. For example a building in St. Petersburg and Oslo have modeled the barcode design.)
What are the advantages of using barcodes?
Advantages of using barcodes at supermarkets:
- The process is much faster for customers than a manual entering of data.
- The burden on the cashiers is minimized since the software performs a lot of tasks simultaneously and at a high speed.
- Accuracy of data is assured.
- Customers are saved from fraud, since they are given details of their purchases.
- It is a good way of compressing a large amount of data.
- It is less costly to the management.
What is a QR code?
Quick Response code is a matrix or 2 dimensional barcode that can store information.
How is it different from barcode?
- The structure - QR code is designed to store more information than a barcode; it is a matrix rather than a series of lines.
- QR code can store 7000 digits, as compared to barcodes, which can store only up to 30.
- QR codes have an error margin ranging from 7-30%, which means that even if there are minor damages made to the code, the scanning would still work.
Where are QR codes used?
- In many supermarkets, they have replaced barcodes for holding information of products.
- They are used by advertisers to reach out to consumers. You may see a code in a newspaper, that you can read by downloading an app on your smartphone.
- They can be used for keeping track of your dietary habits. You can keep track of your calorie intake and nutrition levels by scanning (using the app on a smartphone) the QR code on the items you eat.
- They are printed on business cards to let people get more information about a person or business.
How do digital cameras work?
What exactly happens when picture is taken?
- The lens focus the image onto a mosaic filter. This filter is used for determining the color of the image. It consists o red, green, and blue filters arranged in a Bayer pattern.
- The light then passes through a photosensor. The sensor determines 1. the areas that are dark (since black light reflects no light), and 2. the brightness of the light that falls on it, therefore the brightness of the image.
- The next component is analogue electronics/circuit that converts the data it is receiving to analogue signals.
- The signals are converted to digital signals by a analogue to digital converter.
- The signals are sent to the Digital Image Processor, which edits the data to give a final image. (For example, it uses an algorithm to make certain aspects of the image visible.)
- Next the data is sent to the buffer, which stores the data then sends it to flash memory card. (It stores the data and retains it even when there is no power supply.)
- From the flash memory, the data is displayed onto the LCD/LED screen on your camera.
What are the factors that affect the quality of a photograph?
- Sharpness - How detailed the image is. It is affected by the quality of the lens (its thickness, quality of material and focal length)
- Image noise - Differences in pixel levels. If the density of the pixels in the image is large, then there is high image noise. There are noise filters used to remove this.
- Color - This is how accurately the color of the image is captured. It is affected by the lighting and quality of lens.
- Contrast - Differences in color/lighting that makes objects distinguishable. The quality and size of photosensors affects this feature.
- Vignette - This is the loss of clarity and quality of the image at the corners. It is affected by the quality and size of photosensors, and that of the lens.
What are keyboards?
It is an input device used for entering data into a computable device. They may be a hardware device plugged to a computer (or operating wireless) or a virtual one as in the case of touchscreen devices or a keypads on mobiles.
