Page 174 - DCAP303_MULTIMEDIA_SYSTEMS

Multimedia Systems

notes
figure 10.8: an example of Contrast Correction. Left side of the image is Untouched

Gamma Correction
In addition to the capability of changing the images’ brightness and/or contrast, most current
image editors provide an opportunity to manipulate the images’ gamma value.
Colour adjustments
The colour of images can be altered in a variety of ways. Colours can be faded in and out, and
tones can be changed using curves or other tools. The colour balance can be improved, which is
important if the picture was shot indoors with daylight film, or shot on a camera with the white
balance incorrectly set. Special effects, like sepia and gray scale, can be added to an image. In
addition, more complicated procedures such as the mixing of colour channels are possible using
more advanced graphics editors.
figure 10.9: an example of Colour adjustment Using raster Graphics editor

The red-eye effect, which occurs when flash photos are taken when the pupil is too widely open
(so that light from the flash that passes into the eye through the pupil reflects off the fundus at
the back of the eyeball), can also be eliminated at this stage.

printing
Controlling the print size and quality of digital images requires an understanding of the pixels-
per-inch (ppi) variable that is stored in the image file and sometimes used to control the size of
the printed image. Within the Image Size dialog (as it is called in Photoshop), the image editor
allows the user to manipulate both pixel dimensions and the size of the image on the printed
document. These parameters work together to produce a printed image of the desired size and
quality. Pixels per inch of the image, pixel per inch of the computer monitor, and dots per inch on
the printed document are related, but in use are very different. The Image Size dialog can be used
as an image calculator of sorts. For example, a 1600 × 1200 image with a ppi of 200 will produce
a printed image of 8 × 6 inches. The same image with a ppi of 400 will produce a printed image
of 4 × 3 inches. Change the ppi to 800, and the same image now prints out at 2 × 1.5 inches. All
three printed images contain the same data (1600 × 1200 pixels) but the pixels are closer together

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