An optical scanner is a device designed to convert physical images or text on paper into digital format that computers can process. It achieves this by digitizing the image, essentially converting it into a grid of boxes and assigning each box a value of either zero or one, representing whether the box is filled in or not. This process is applicable to color and grayscale images as well, where each box may be represented by up to 24 bits to capture the color information accurately. The resulting collection of bits forms a bitmap, which can be saved in a file, displayed on a screen, or manipulated using software programs.
It’s important to note that optical scanners do not differentiate between text and illustrations; they treat all images as bitmaps. Therefore, direct editing of scanned text is not possible. To edit scanned text, Optical Character Recognition (OCR) systems are used to convert the image into ASCII characters. Many modern optical scanners come bundled with OCR software to facilitate text editing.
Optical scanners vary in several aspects:
- Scanning Technology: Most scanners utilize Charge-Coupled Device (CCD) arrays, consisting of closely packed rows of light receptors capable of detecting variations in light intensity and frequency. The quality of the CCD array significantly impacts scanner performance. Higher-end drum scanners use Photomultiplier Tube (PMT) technology, but these are costlier than CCD-based scanners.
- Resolution: The resolution of a scanner determines the density of the bitmap and is measured in dots per inch (dpi). Scanners typically support resolutions ranging from 72 to 600 dpi, with higher resolutions producing sharper images.
- Bit Depth: This refers to the number of bits used to represent each pixel in the bitmap. A higher bit depth allows for more colors or grayscale levels to be represented accurately. For example, a 24-bit color scanner can capture 16.7 million colors. However, the effectiveness of a large color range depends on the CCD’s ability to detect distinct colors.
- Size and Shape: Scanners vary in size and design. Hand-held scanners are compact and suitable for small images but may be challenging to use for scanning entire pages. Sheet-fed scanners are larger and can process loose sheets of paper efficiently. Flatbed scanners, resembling photocopy machines, are ideal for scanning books, magazines, and other bound documents.