Image presentation
- 1. Image Presentation vectors and rasters
- 2. digital imaging Digital imaging is the creation of digital images, typically from a physical scene. The term is often assumed to imply or include the processing, compression, storage, printing, and display of such images. The most usual method is by digital photography with a digital camera but other methods are also employed. A digital photograph may be created directly from a physical scene by a camera or similar device. It is used to pass some kind of information to the viewers. there are two types of digital images. one is raster images and the other is vector images.
- 3. vector images A vector image is a collection of connected lines and curves that produce objects. When creating a vector image in a vector illustration program, node or drawing points are inserted and lines and curves connect notes together. This is the same principle as "connect the dots". Each node, line and curve is defined in the drawing by the graphics software by a mathematical description. Every aspect of a vector object is defined by math included node position, node location, line length and on down the line.
- 4. advantages of vectors Data can be represented at its original resolution and form without generalization. Graphic output is usually more aesthetically pleasing (traditional cartographic representation); Since most data, e.g. hard copy maps, is in vector form no data conversion is required. Accurate geographic location of data is maintained. Allows for efficient encoding of topology, and as a result more efficient operations that require topological information, e.g. proximity, network analysis.
- 5. disadvantages of vectors The location of each vertex needs to be stored explicitly. For effective analysis, vector data must be converted into a topological structure. This is often processing intensive and usually requires extensive data cleaning. As well, topology is static, and any updating or editing of the vector data requires re-building of the topology. Algorithms for manipulative and analysis functions are complex and may be processing intensive. Often, this inherently limits the functionality for large data sets, e.g. a large number of features. Continuous data, such as elevation data, is not effectively represented in vector form. Usually substantial data generalization or interpolation is required for these data layers. Spatial analysis and filtering within polygons is impossible
- 6. raster images A raster image is a collection of dots called pixels. Each pixel is a tiny colored square. When an image is scanned, the image is converted to a collection of pixels called a raster image. Scanned graphics and web graphics (JPEG and GIF files) are the most common forms of raster images. Web graphics, including JPEG and GIF files, are always low-resolution raster images. For this reason, web graphics are always a poor choice for imprinting and editing. Production-ready clip art is an essential tool for creating high quality imprints.
- 7. advantages of rasters The geographic location of each cell is implied by its position in the cell matrix. Accordingly, other than an origin point, e.g. bottom left corner, no geographic coordinates are stored. Due to the nature of the data storage technique data analysis is usually easy to program and quick to perform. The inherent nature of raster maps, e.g. one attribute maps, is ideally suited for mathematical modeling and quantitative analysis. Discrete data, e.g. forestry stands, is accommodated equally well as continuous data, e.g. elevation data, and facilitates the integrating of the two data types. Grid-cell systems are very compatible with raster-based output devices, e.g. electrostatic plotters, graphic terminals.
- 8. disadvantages of rasters The cell size determines the resolution at which the data is represented.; It is especially difficult to adequately represent linear features depending on the cell resolution. Accordingly, network linkages are difficult to establish. Processing of associated attribute data may be cumbersome if large amounts of data exists. Raster maps inherently reflect only one attribute or characteristic for an area. Since most input data is in vector form, data must undergo vector-to-raster conversion. Besides increased processing requirements this may introduce data integrity concerns due to generalization and choice of inappropriate cell size. Most output maps from grid-cell systems do not conform to high-quality cartographic needs.
- 9. GIF format The GIF name is a acronym for Graphics Interchange Format, and was first introduced by Compuserve in 1987. This is a popular format next to the JPEG format and is still used on Web pages today. Digital cameras, however, don’t use this format because it only supports 256 colours. There are currently two versions of GIF in use: GIF87a (the original version) and GIF89a. The GIF89a version supports multiple images in stream which allows you to create animated GIF images. Advantages – One advantage to a GIF is that it uses lossless compression to make an image smaller. This means that no image information is lost during compression. It also has the advantage of making one of the colours in the image transparent to allow the background to show through. As mentioned earlier, you can create simple animations by combining multiple images into a single GIF89a file. Disadvantages – The biggest disadvantage for the GIF file format is that it only supports 256 colours, which isn’t nearly enough for a digital photo. This means that GIF files are restricted to sharp-edged line art (such as logos) that have a limited number of colours.
- 10. JPEG format This is perhaps the most popular file format used for digital pictures, especially now that all digital cameras store their pictures in this format. Similar to GIF, JPEG is also an acronym for Joint Photographic 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 million colours. This is more than enough for a digital photo. Besides the number of colours, another difference between the GIF format and the JPEG format is the type of compression used. While a GIF uses a lossless compress, a JPEG file is compressed using a lossy compression algorithm. This means that 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 the Internet. For more information about the JPEG and RAW file formats, please read JPEG or RAW Format. Advantages – The biggest advantage is the ability to save a digital photo in a very small size (in bytes). 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 reasons alone. 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 you compress an image too much, you will get JPEG "artifacts". These look like distorted sections of the images, 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.
- 11. TIFF format As with many names in the computer world, the TIFF name is also an acronym. TIFF is short for Tagged Image File Format. This a very popular format for archiving digital photos, mainly because it is widely supported by most image editing programs across many different operating systems. Similar to the JPEG format, it supports 24-bit (16.7 million) colours. You can even save up to 48-bits of colour information within the file. The trade off is the file size. While JPEG files are compressed, TIFF files are generally uncompressed, which results in very large file 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 on many different operating systems, it is the first choice for archiving digital photos. Since TIFFs don’t use compression, at least by default, you can continuously save a TIFF file and never lose any information. When editing photos, it is best to first save the file in a TIFF format 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 save your photo archives in the TIFF format. d