Page 13 - DCAP504_Computer Graphics

Computer Graphics

A typical contour image representation is clearly depicted in the figure 1.2.

Figure 1.2: Contour Image Representation

A contour representation helps in easy recovery of the full image in bitmap form. It has been used
mainly for data compression of an image. The main idea is to program each level with the boundaries of
connected regions of pixels at levels superior than or equal to each level. It is easy to recreate an original
image from these boundaries.

One of the main issues in using contour image representations is how to save such representations in a
compact manner. In practice, the complete contour representation is hardly ever required. Its distinctive
use is in the form of a query, where it asks for the contours matching for a given gray level. To provide
efficient solutions, the current data structuring techniques should be used. However, they have not yet
been used, but attempts are being made in order to solve this.

Consider a typical scenario encountered with this kind of representation.
Presume that you want to erase wrinkles around the eyes of a person in a

digitized picture given in contour representation. As the image of the wrinkles
may intersect contour lines, these may appear to be detached after removal of the
wrinkles. It is not easy to reconnect these contour lines. Dynamic programming
might be a normal approach to solve this problem.
Note: The dynamic programming has been tried in numerous experiments
effectively. The only drawback of dynamic programming is that it is very costly.
In fact, the total number of pixels in an image is a function of the size of the image and the number of
pixels per unit length, such as inch in the horizontal as well as the vertical direction. This number of
pixels per unit length is the resolution of the image.

A 3×2 inch image at a resolution of 300 pixels per inch would have a total of 5,
40,000 pixels.
In general, the image size is given as the total number of pixels in the horizontal direction multiplied by
the total number of pixels in the vertical direction, such as 512×512, 640×480, 800×600, or 1024×768.
Even though, this convention makes it comparatively easy to measure the total number of pixels in an
image, it does not specify the size of the image or its resolution.

A 640×480 image would measure 62/31 inches by 5 inches when displayed or
printed at 96 pixels per inch. Alternatively, the same image would measure 1.6

inches × 1.2 inches at 400 pixels per inch.
The ratio or the proportion of an image’s width to its height, measured in unit length or number of
pixels, is referred to as aspect ratio.

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