Image Capture

Scanner

A scanner is a device that creates digital versions of photographs or written work by scanning them and converting it into a digital file. This file can then be viewed and edited on the computer like other image files, and it would typically be saved as a JPEG file. Scanners are usually flatbed devices, meaning they have a flat scanning surface that makes it easier to scan things such as books or magazines. When a scanner is bought, it will come with software that needs to be installed first before it can work. This software imports data from the scanner and allows the user to initiate and configure scans. The scanning process consists of several stages. Firstly, the document is placed on the glass plate and the cover closed. The cover is usually white, and provides a uniform background colour that the scanner can use as a reference to determine the documents size. Next, the document is illuminated by a lamp which may be cold cathode fluorescent lamp, or a xenon lamp. Scanning can then proceed, and the scan head (Which consists of mirrors, the lens, the filter and the CCD Array) moves slowly along the document until it achieves a pass; a single total scan of the document. A curved mirror (Curved to focus the image) then reflects the image onto another curved mirror, and then onto the lens. The lens then focuses the image through a filter on the CCD Array.

Older scanners worked using a three pass technique. This is where the Scan Head needs to make 3 complete scans of the document, one for each colour filter; Red, Green and Blue. Once the scans are complete the 3 images are assembled into 1 fully coloured image. Nowadays scanners often use a 1 pass technique where the Lens splits the image into 3 smaller versions, and these are put through a colour filter. The image is then combined into a full-colour version. The parts that make up a scanner are; the Charged Coupled Device (CCD) Array, Mirrors, the Scan Head, the Lens, Filters, a Glass Plate, Lamp, and Cover, the Stepper Motor, Stabilizer bar, a belt, and finally the power supply, interface ports and control circuitry. The most important feature is the CCD array, which is the part that allows for image capture. It consists of many Light Sensitive Diodes, called Photosites. The final aspect is image transfer, which is commonly done by USB connection as it is efficient and affordable, however methods like Small Computer System Interface or FireWire are used too. Also, driver software needs to be installed that can communicate with the scanner. Scanners know the language TWAIN, and the TWAIN driver acts as an interpreter between the computer and the scanner.

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Digital Camera

The digital camera is a device that can take photographs and store them digitally so they can be transferred on to a computer and be viewed or edited there. Digital cameras feature built in computers and capture images electronically. When a digital camera takes a photo, it samples the light coming from an object, and breaks the light down into a series of pixel values. It is recorded in a digital form that consists of a long string of binary code, and these represent the information in each of the pixels in the photo. The camera breaks light into electrical charges by using sensors, this censor is usually a CCD or Charged Coupled Device. This is, put simply, like an array of millions of tiny solar cells that convert light into electrons. When a camera takes a photo, the detail is determined by the amount of pixels used for the photo; it's Resolution. Mote pixels mean a better quality images. On a good camera, resolutions of at least 1600 x 1200 would be used, with top of the range cameras using as high as 4064 x 2704.

On a digital camera, the one way to capture colour is to use three sensors each with a different colour filter; red, green or blue. A Beam Splitter is used to split the light equally between the filters, each of which sees the same image but only in the colour of the filter. They are then combined to create a full colour image. The best way however is to use a colour filter array placed over each photosite. The colour filter array breaks a sensor up into red, green and blue pixels and enables it to make a very accurate guess about the true colour of an object according to other pixels near the sensor. This process is called Interpolation, and allows for smaller, cheaper cameras. Demosaicing Algorithms are used to convert this mosaic into a full colour version, on the basis that each coloured pixel can be used over and over. Colours for one pixel are found by getting an average of values from surrounding pixels. Once a photo is taken, it can be viewed immediately on the LCD screen, but it can also be sent to a computer via USB or other methods. Typically this means the photo must be converted to a file format suitable for storing and transferring to a PC. Common file types used are TIFF, and JPEG as they create high quality images (Although TIFF files have a large file size).
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