Page 173 - DCAP303_MULTIMEDIA_SYSTEMS

Unit 10: 3D Modelling and Animation Tools

special effects notes
Image editors usually have a list of special effects that can create unusual results. Images may be
skewed and distorted in various ways. Scores of special effects can be applied to an image which
includes various forms of distortion, artistic effects, geometric transforms and texture effects, or
combinations thereof.
figure 10.6: an example of some special effects that can be added to a picture

Change Colour Depth

It is possible, using software, to change the colour depth of images. Common colour depths are
2, 4, 16, 256, 65,536 and 16.7 million colours. The JPEG and PNG image formats are capable of
storing 16.7 million colours (equal to 256 luminance values per colour channel). In addition, gray
scale images of 8 bits or less can be created, usually via conversion and down-sampling from a
full-colour image.
figure 10.7: an example of Converting an image from Colour to Gray scale

Contrast Change and Brightening
Image editors have provisions to simultaneously change the contrast of images and brighten or
darken the image. Underexposed images can often be improved by using this feature. Recent
advances have allowed more intelligent exposure correction whereby only pixels below a particular
luminosity threshold are brightened, thereby brightening underexposed shadows without affecting
the rest of the image. The exact transformation that is applied to each colour channel can vary
from editor to editor. GIMP applies the following formula:
if (brightness < 0.0) value = value * ( 1.0 + brightness);
else value = value + ((1 - value) * brightness);
value = (value - 0.5) * (tan ((contrast + 1) * PI/4) ) + 0.5;
where, value is the input colour value in the 0..1 range and brightness and contrast are in the
-1..1 range.

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