Page 54 - DCAP303_MULTIMEDIA_SYSTEMS

Multimedia Systems

notes
figure 4.9: 16 Bit rGB

4.1.2 resolution
Resolution is an attribute of a bitmap that is necessary when visually viewing or printing bitmaps
because pixels by themselves have no explicit dimensions. Resolution is normally specified in
pixels per inch but could be in terms of any other unit of measure. Most printing processes retain
the pixels per inch (PPI) units for historical reasons. On devices with non-rectangular pixels, the
resolution may be specified as two numbers, the horizontal and vertical resolution.

The concept of resolution being independent of the information content of a bitmap is very
important, given a constant colour depth then the information content between different bitmaps
is only related to the number of pixels vertically and horizontally. The quality however, when the
bitmap is displayed or printed, does depend on the resolution. Since the resolution determines
the size of a pixel, it can also be used to modify the size of the overall image.
As an example, consider one bitmap which is 200 pixels horizontally and 100 pixels vertically.
If this bitmap was printed at 100 DPI then it would measure 2 inches by 1 inch. If, however, the
same bitmap was printed at 200 DPI (See Figure 4.10) then it would only measure 1 inch by half
an inch.
figure 4.10: resolution of Bitmap

Whenever a bitmap is displayed on a computer monitor resolution need to be considered. Most
computer monitors have a range of resolution from 60 DPI at the low resolution end to 120 DPI
for high resolution displays. As with printed matter the higher the resolution, the less apparent
the pixel nature of the bitmap will be.

As a further example the following (See Figure 4.11) two images are identical in information
content, they do however have different resolutions and hence different pixel sizes. The smaller
is 80 DPI, the larger is 30 DPI. The pixels are much more evident in the larger version.

48 LoveLy professionaL University