digital imagingDigital imaging is the creation of digital images, typically from a physical scene. The termis often assumed to imply or include the processing, compression, storage, printing, anddisplay of such images. The most usual method is by digital photography with a digitalcamera but other methods are also employed.A digital photograph may be created directly from a physical scene by a camera orsimilar device. It is used to pass some kind of information to the viewers. there are twotypes of digital images. one is raster images and the other is vector images.
vector imagesA vector image is a collection of connected linesand curves that produce objects. When creatinga vector image in a vector illustration program,node or drawing points are inserted and linesand curves connect notes together. This is thesame principle as "connect the dots". Each node,line and curve is deﬁned in the drawing by thegraphics software by a mathematicaldescription. Every aspect of a vector object isdeﬁned by math included node position, nodelocation, line length and on down the line.
advantages of vectors Data can be represented at its original resolution and form withoutgeneralization. Graphic output is usually more aesthetically pleasing(traditional cartographic representation); Since most data, e.g. hardcopy maps, is in vector form no data conversion is required. Accurategeographic location of data is maintained. Allows for efﬁcient encodingof topology, and as a result more efﬁcient operations that requiretopological information, e.g. proximity, network analysis.
disadvantages of vectors The location of each vertex needs to be stored explicitly. For effectiveanalysis, vector data must be converted into a topological structure.This is often processing intensive and usually requires extensive datacleaning. As well, topology is static, and any updating or editing of thevector data requires re-building of the topology. Algorithms formanipulative and analysis functions are complex and may beprocessing intensive. Often, this inherently limits the functionality forlarge data sets, e.g. a large number of features. Continuous data, suchas elevation data, is not effectively represented in vector form. Usuallysubstantial data generalization or interpolation is required for thesedata layers. Spatial analysis and ﬁltering within polygons is impossible
raster imagesA raster image is a collection of dots calledpixels. Each pixel is a tiny colored square.When an image is scanned, the image isconverted to a collection of pixels called araster image. Scanned graphics and webgraphics (JPEG and GIF ﬁles) are the mostcommon forms of raster images.Web graphics, including JPEG and GIF ﬁles,are always low-resolution raster images.For this reason, web graphics are always apoor choice for imprinting and editing.Production-ready clip art is an essential toolfor creating high quality imprints.
advantages of rasters The geographic location of each cell is implied by its position in thecell matrix. Accordingly, other than an origin point, e.g. bottom leftcorner, no geographic coordinates are stored. Due to the nature ofthe data storage technique data analysis is usually easy toprogram and quick to perform. The inherent nature of raster maps, e.g. one attribute maps, isideally suited for mathematical modeling and quantitativeanalysis. Discrete data, e.g. forestry stands, is accommodatedequally well as continuous data, e.g. elevation data, and facilitatesthe integrating of the two data types. Grid-cell systems are verycompatible with raster-based output devices, e.g. electrostaticplotters, graphic terminals.
disadvantages of rastersThe cell size determines the resolution at which the data isrepresented.; It is especially difﬁcult to adequately representlinear features depending on the cell resolution. Accordingly,network linkages are difﬁcult to establish. Processing ofassociated attribute data may be cumbersome if large amounts ofdata exists. Raster maps inherently reﬂect only one attribute orcharacteristic for an area. Since most input data is in vector form,data must undergo vector-to-raster conversion. Besides increasedprocessing requirements this may introduce data integrityconcerns due to generalization and choice of inappropriate cellsize. Most output maps from grid-cell systems do not conform tohigh-quality cartographic needs.
GIF format The GIF name is a acronym for Graphics Interchange Format, and was ﬁrstintroduced by Compuserve in 1987. This is a popular format next to the JPEGformat and is still used on Web pages today. Digital cameras, however, don’t usethis format because it only supports 256 colours.There are currently two versions of GIF in use: GIF87a (the original version) andGIF89a. The GIF89a version supports multiple images in stream which allowsyou to create animated GIF images.Advantages – One advantage to a GIF is that it uses lossless compression tomake an image smaller. This means that no image information is lost duringcompression. It also has the advantage of making one of the colours in the imagetransparent to allow the background to show through. As mentioned earlier, youcan create simple animations by combining multiple images into a single GIF89aﬁle.Disadvantages – The biggest disadvantage for the GIF ﬁle format is that it onlysupports 256 colours, which isn’t nearly enough for a digital photo. This meansthat GIF ﬁles are restricted to sharp-edged line art (such as logos) that have alimited number of colours.
JPEG formatThis is perhaps the most popular ﬁle format used for digital pictures, especially now that all digitalcameras store their pictures in this format. Similar to GIF, JPEG is also an acronym for JointPhotographic Experts Group. This group was ﬁrst formed in 1986, issued a standard in 1992,which was approved in 1994.Unlike the GIF ﬁle format, the JPEG format can compress images that contain up to 16.7 millioncolours. This is more than enough for a digital photo. Besides the number of colours, anotherdifference between the GIF format and the JPEG format is the type of compression used. While a GIFuses a lossless compress, a JPEG ﬁle is compressed using a lossy compression algorithm. This meansthat each time you save a JPEG ﬁle, it loses more information.Digital cameras may also have the ability to save a picture in the RAW format. This format, however,is a proprietary format that is different between cameras manufacturers, so it isn’t used at all on theInternet. For more information about the JPEG and RAW ﬁle formats, please read JPEG or RAWFormat.Advantages – The biggest advantage is the ability to save a digital photo in a very small size (inbytes). Another advantage is that it can save an image that includes up to 16.7 million colours,which is more than enough for a digital picture. It is a very popular format for those two reasonsalone.Disadvantages – The biggest disadvantage is that the compression used in a JPEG image is lossy.Each time you save a JPEG image, the more data you lose. Another disadvantage is that if youcompress an image too much, you will get JPEG "artifacts". These look like distorted sections of theimages, usually looking like squares. You should minimize the amount of compression of the image,while at the same time managing the size of the ﬁle, to reduce these artifacts.
TIFF formatAs with many names in the computer world, the TIFF name is also an acronym. TIFF isshort for Tagged Image File Format. This a very popular format for archiving digitalphotos, mainly because it is widely supported by most image editing programs acrossmany different operating systems.Similar to the JPEG format, it supports 24-bit (16.7 million) colours. You can even saveup to 48-bits of colour information within the ﬁle. The trade off is the ﬁle size. While JPEGﬁles are compressed, TIFF ﬁles are generally uncompressed, which results in very largeﬁle sizes. You can, however, compress TIFF ﬁles but not to the same size of JPEGs.Advantages – Since the TIFF ﬁle format is supported by pretty much all image editors onmany different operating systems, it is the ﬁrst choice for archiving digital photos. SinceTIFFs don’t use compression, at least by default, you can continuously save a TIFF ﬁle andnever lose any information. When editing photos, it is best to ﬁrst save the ﬁle in a TIFFformat during editing, and then JPEG once your are ﬁnished.Disadvantages – The biggest disadvantage for a TIFF ﬁle is the size. Compared to JPEGs,TIFF ﬁles are enormous. Depending on the bit depth (24 or 48) you are talking 100MB+for a single ﬁle. Although, with the size of hard drives and DVDs it will be worth it to saveyour photo archives in the TIFF format. d