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. Ever y
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.
In order to view on a computer screen, they must be
converted in the monitor resolution. the computer must
recalculate the number of pixels every time it refreshes.
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.
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.
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.
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.
