Page 172 - DCAP303_MULTIMEDIA_SYSTEMS

Multimedia Systems

notes enhancing images
In computer graphics, the process of improving the quality of a digitally stored image by
manipulating the image with software. It is quite easy, for example, to make an image lighter or
darker, or to increase or decrease contrast. Advanced photo enhancement software also supports
many filters for altering images in various ways. Programs specialized for image enhancements
are sometimes called image editors.

sharpening and softening images
Graphics programs can be used to both sharpen and blur images in a number of ways, such as
un-sharp masking or de-convolution. Portraits often appear more pleasing when selectively
softened (particularly the skin and the background) to better make the subject stand out. This can
be achieved with a camera by using a large aperture, or in the image editor by making a selection
and then blurring it. Edge enhancement is an extremely common technique used to make images
appear sharper, although purists frown on the result as appearing unnatural.
selecting and Merging of images

Many graphics applications are capable of merging one or more individual images into a single
file. The orientation and placement of each image can be controlled.
figure 10.5: photomontage of 16 photos which have been Digitally Manipulated in
photoshop to give the impression that it is a real Landscape

When selecting a raster image that is not rectangular, it requires separating the edges from the
background, also known as silhouetting. This is the digital version of cutting out the image.
Clipping paths may be used to add silhouetted images to vector graphics or page layout files that
retain vector data. Alpha compositing allows for soft translucent edges when selecting images.
There are a number of ways to silhouette an image with soft edges including selecting the image
or its background by sampling similar colours, selecting the edges by raster tracing, or converting
a clipping path to a raster selection. Once the image is selected, it may be copied and pasted into
another section of the same file, or into a separate file. The selection may also be saved in what
is known as an alpha channel.
A popular way to create a composite image is to use transparent layers. The background image
is used as the bottom layer, and the image with parts to be added are placed in a layer above
that. Using an image layer mask, all but the parts to be merged are hidden from the layer, giving
the impression that these parts have been added to the background layer. Performing a merge
in this manner preserves all of the pixel data on both layers to more easily enable future changes
in the new merged image.
slicing of images
A more recent tool in digital image editing software is the image slicer. Parts of images for graphical
user interfaces or Web pages are easily sliced, labelled and saved separately from whole images
so the parts can be handled individually by the display medium. This is useful to allow dynamic
swapping via interactivity or animating parts of an image in the final presentation.

166 LoveLy professionaL University