Page 170 - DCAP303_MULTIMEDIA_SYSTEMS

Multimedia Systems

notes for Internet use. Image editor programs use a mathematical process called resampling to calculate
new pixel values whose spacing is larger or smaller than the original pixel values. Images for
Internet use are kept small, say 640 x 480 pixels which would equal 0.3 megapixels.

Cropping an image
Digital editors are used to crop images. Cropping creates a new image by selecting a desired
rectangular portion from the image being cropped. The unwanted part of the image is discarded.
Image cropping does not reduce the resolution of the area cropped. Best results are obtained when
the original image has a high resolution. A primary reason for cropping is to improve the image
composition in the new image.

Histogram
Image editors have provisions to create an image histogram of the image being edited. The
histogram plots the number of pixels in the image (vertical axis) with a particular brightness value
(horizontal axis). Algorithms in the digital editor allow the user to visually adjust the brightness
value of each pixel and to dynamically display the results as adjustments are made. Improvements
in picture brightness and contrast can thus be obtained.
noise reduction
Image editors may feature a number of algorithms which can add or remove noise in an image.
The JPEG artifacts can be removed; dust and scratches can be removed and an image can be de-
speckled. Noise reduction merely estimates the state of the scene without the noise and is not a
substitute for obtaining a “cleaner” image. Excessive noise reduction leads to a loss of detail, and
its application is hence subject to a trade-off between the undesirability of the noise itself and
that of the reduction artifacts.

Noise tends to invade images when pictures are taken in low light settings. A new picture can be
given an ‘antiquated’ effect by adding uniform monochrome noise.

removal of Unwanted elements
Most image editors can be used to remove unwanted branches, etc., using a “clone” tool. Removing
these distracting elements draws focus to the subject, improving overall composition.

figure 10.1: (a) notice the Branch in (b) the eye is Drawn to the Centre

the original of the Globe

selective Colour Change
Some image editors have colour swapping abilities to selectively change the colour of specific
items in an image, given that the selected items are within a specific colour range.

164 LoveLy professionaL University