Glossary
Digital Photography Terms |
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| Term | Definition |
| Aperture | The opening in the lens that controls how much light hits the camera's image sensor. The aperture is an iris in the lens that can be opened or closed to allow more or less light into the camera. The smaller the aperture the less light it allows to enter through the lens. This is one of the ways a camera regulates exposure. |
| Artefact | Misinterpreted information from a JPEG or a similarly compressed image; includes defects that appear in an image as colour flaws or skewed lines. |
| CCD | Charge Coupled Device. This the light sensitive device in most all digital cameras that turns the light entering though the lens into electronic signals that can be digitally processed and saved; a mechanism that converts light into a proportional (analog) electrical current; the two main types of CCD are linear arrays, used in flatbed scanners and digital copiers, and area arrays, found in camcorders, digital cameras, and the like. |
| GIF | GIF (Graphics Interchange Format) is limited to an 8-bit palette, or 256 colors. This makes the GIF format suitable for storing graphics with relatively few colors such as simple diagrams, shapes, logos and cartoon style images. The GIF format supports animation and is still widely used to provide image animation effects. It also uses a lossless compression that is more effective when large areas have a single color, and ineffective for detailed images or dithered images. |
| jpeg | JPEG (Joint Photographic Experts Group) files are (in most cases) a lossy format; the DOS filename extension is JPG (other OS might use JPEG). Nearly every digital camera can save images in the JPEG format, which supports 8 bits per color (red, green, blue) for a 24-bit total, producing relatively small files. When not too great, the compression does not noticeably detract from the image's quality, but JPEG files suffer generational degradation when repeatedly edited and saved. Photographic images may be better stored in a lossless non-JPEG format if they will be re-edited, or if small "artifacts" (blemishes caused by the JPEG's compression algorithm) are unacceptable. The JPEG format also is used as the image compression algorithm in many Adobe PDF files. |
| MegaPixel | Instead of using film, digital cameras capture images with a sensor. Usually, the sensor used is called a CCD (though some manufacturers use CMOS sensors instead). Either way, the sensor is comprised of an array of light-sensing dots, called pixels (short for "picture elements"). A camera's resolution is simply the total number of pixels packed onto the CCD. Resolution is measured in two different ways--either as a pair of numbers signifying width times height (for example, 1,600 x 1,200) or as a total number of pixels. To convert from the first measurement method to the second, simply multiply the width by the height. In the previous example, 1,600 x 1,200 is approximately 2 million, indicating that this is a 2-megapixel (2-million-pixel) camera. Today's consumer cameras range from 640 x 480 (0.3 megapixels) to 2,048 x 1,536 (3.3 megapixels). |
| Raw | A raw image file contains minimally processed data from the image sensor of either a digital camera, image or motion picture film scanner. Raw files are so named because they are not yet processed and therefore are not ready to be used with a bitmap graphics editor or printed. Normally, the image is processed by a raw converter in a wide-gamut internal colorspace where precise adjustments can be made before conversion to a "positive" file format such as TIFF or JPEG for storage, printing, or further manipulation, which often encodes the image in a device-dependent colorspace. These images are often described as "RAW image files" based on the erroneous belief that they represent a single file format. In fact there are dozens if not hundreds of raw image formats in use by different models of digital equipment (like cameras of film scanners). Raw image files are sometimes called digital negatives, as they fulfill the same role as negatives in film photography: that is, the negative is not directly usable as an image, but has all of the information needed to create an image. Likewise, the process of converting a raw image file into a viewable format is sometimes called developing a raw image, by analogy with the film development process used to convert photographic film into viewable prints. The selection of the final choice of image rendering is part of the process of white balancing and color grading. Like a photographic negative, a raw digital image may have a wider dynamic range or color gamut than the eventual final image format, and is usually the one "closest" to the real picture in the sense that is preserves the most of its details. Raw image formats' purpose is to faithfully record both 100% of exactly what the sensor "saw" or "sensed" (the data), and the conditions surrounding the recording of the image (the metadata). |
| TIFF | The TIFF (Tagged Image File Format)is a flexible format that normally saves 8 bits or 16 bits per color (red, green, blue) for 24-bit and 48-bit totals, respectively, using either the TIFF or the TIF filenames. The TIFF's flexibility is both blessing and curse, because no single reader reads every type of TIFF file. TIFFs are lossy and lossless; some offer relatively good lossless compression for bi-level (black&white) images.Some digital cameras can save in TIFF format, using the LZW compression algorithm for lossless storage. The TIFF image format is not widely supported by web browsers. TIFF remains widely accepted as a photograph file standard in the printing business. The TIFF can handle device-specific colour spaces, such as the CMYK defined by a particular set of printing press inks. |
| Glossary V2.0 | |
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