17. What is the work of a modem?
Ans. Modem word is derived from modulator/demodulator. In electronics, modulation is a predecided change in output for a change in input. The digital signals produced in a computer are not suitable for transmission by long telephone wires. There are good chances of errors in received signals. So the digital signals are changed to a suitable analog form or modulated before transmitting by telephone wires. The received analog signals are demodulated to produce original signal suitable for computer.
18. When should I use GIF format for my image ?
Ans. GIF is a lossless method of compressing an image file. Lossless methods of compression can not achieve reduction of file size more than 2 to 3 times. If an image is created in a computer, it is most likely to have less than 255 different colors. Clipart pictures/drawings, paintbrush drawings and other such software generated images can be saved in GIF format. A BMP (bit mapped image) file opened and saved in GIF format reduces file size by a factor of 2 to 3. The resulting image retains all the features of the original image. But there may be a typical problem. One or two colors used in the original BMP image may change to nearby color value.This happens when a color used is not exactly same as any of the 255 colors chosen by the drawing software for the purpose of storing in GIF files. In such a case, the nearest color value is chosen to replace the original one. But GIF compression method is lossless or distortionfree. A text file is compressed or zipped by similar principles of compression.
19. When should I use JPEG format for my image ?
Ans. JPEG or JPG format can provide high compression levels. In images where more than 255 colors are used, JPEG compression is used. Digital cameras, Scanners, satellite image data etc contain many, many different colors. Each pixel color may be different from colors of nearby pixels. In such applications, GIF compression can not yield appreciable reduction in file size. However, JPEG compression method is lossy. At lower compression levels, loss is imperceptible. In all cases, compressed image pixels retain the overall features of color distribution. There may be visible distortion at edges or where color changes drastically. JPEG compression method allows highier or lower degree of compression depending on the satisfaction level of the user. An image file may be compressed by a factor of 10 without any perceptible distortion. Internet accepts both JPEG and GIF images, as the image files are compressed.
20. How do I produce a nonrectangular image?
Ans. All images are basically rectangular. The unwanted pixels around a nonrectangular area can be rejected in the following way. Open the image in a photoeditor or paintbrush. Cut or copy a narrow rectangular area around the desired part. Paste it as a fresh image. Choose a color of the background around the desired cutout. In most applications, the background color is white, black or a single color. Within the rectangular frame change the color of the unwanted pixels with a single chosen color. Do not disturb the colors of the pixels within the desired area. From the toolbars choose transparent color, point within the discolored region to apply transparency. Save the file as GIF file only. No other file format is suitable for transparency of unwanted areas. The saved image will still be rectangular, but rejected areas will not appear on the background, wherever it is placed. The background areas need not be composed of a single color. An example would be superimposition of your face cutout from any picture in the above way, on a picture of clouds |
