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by Dinesh Thakur

The process by which CONTINUOUS TONE photographs are reproduced in print (for example in newspapers and magazines) by reducing them to a grid of tiny dots. (The resulting image is also commonly known as a halftone.) Each individual dot is printed using a single coloured ink of fixed intensity, and the intensity of colour the reader perceives is controlled by varying the size and density of the dots to reveal more or less of the underlying white paper.

 
by Dinesh Thakur

An algorithm employed in 3D GRAPHICS to fool the eye into seeing as a smoothly curving surface an object that is actually constructed from a mesh of polygons. Gouraud's algorithm requires the colour at each vertex of a polygon to be supplied as data, from which it INTERPOLATES the colour of every PIXEL inside the polygon: this is a relatively fast procedure, and may be made faster still if implemented in a hardware GRAPHICS ACCELERATOR chip. 

 
by Dinesh Thakur

Ray tracing is an incredibly complex method of producing shadows, reflections, and refractions in high-quality, three-dimensionally simulated computer graphics. Ray tracing calculates the brightness, the reflectivity, and the transparency level of every object in the image. And it does this backwards. That is, it traces the rays of light back from the viewer's eye to the object from which the light was bounced off from the original light source, taking into consideration along the way any other objects the light was bounced off or refracted through .



 
by Dinesh Thakur

To understand what rasterizing does, first you need to know a little about the images in the computer: Bitmapped (raster) graphics and fonts are created with tiny little dots. Object-oriented (vector) graphics and fonts are created with outlines. Output devices, like printers (except for some plotters) and monitors can only print or display images using dots, not outlines. This means that when an object-oriented graphic or font is output to a printer that prints in dots per inch (as most of them do) or to a monitor that displays in pixels (as most of them do), the outlines must be turned into dots. This process of turning the outlines of the objects into dots is called rasterizing. Everything you see on your monitor has been rasterized. Everything you print has been rasterized.



 
by Dinesh Thakur

Some computer screens are grayscale, rather than plainblack-and white (monochrome). On a black-and-white screen, there is only one bit of information being sent to each pixel (dot), so the pixels on the screen are either on (white) or off (black). On a greyscale monitor, anywhere from 2 to 16 bits of information are sent to each pixel, so it is possible to display gray tones in the pixels, rather than just black or white.



 
by Dinesh Thakur

On a piece of photographic film, such as the kind you use to shoot photographs, one side of the film is coated with a layer of chemicals called the emulsion. This is the side that absorbs the light, and the emulsion is scratch able and dull. The non-emulsion side of film looks shinier and is more difficult to scratch. You can see the emulsion side on any negative you have hanging around.

 
by Dinesh Thakur

Early computer-generated images used shaded objects that had unnaturally smooth surfaces. To produce a textured surface using the techniques discussed would require creating an excessive number of surface pieces that follow all of the complexities of the texture. An alternative to the explosion of surfaces would be to use the techniques of texture mapping. Texture mapping is a technique used to paint scanned images of a texture onto the object being modeled. Through an associated technique, called bump mapping, the appearance of the texture can be improved still further.

 
by Dinesh Thakur

A problem with the Painter's and Z-Buffer Algorithms is that they ignore the effects of the light source and use only the ambient light factor. Flat shading goes a bit further and includes the diffuse reflections as well. For each of the planar pieces, an intensity value is calculated from the surface normal, the direction to the light, and the ambient light and diffuse coefficient constants. Since none of these changes at any point on the piece, all of the pixels in that piece will have the same intensity value. The resulting image will appear to be faceted, with ridges running along the boundaries of the pieces that make up an object.

 
by Dinesh Thakur

An extra layer of information stored in a digital picture to describe transparency or opacity. For each pixel, the alpha channel stores an extra value called alpha, in addition to its red, blue and green values, which indicates the degree of transparency of that pixel.



 
by Dinesh Thakur

What is transformation? In  many  cases  a  complex  picture  can  always  be  treated as  a  combination  of  straight line, circles, ellipse etc., and if we are able to generate these basic figures, we can also generate combinations of them.  Once we  have drawn these pictures, the  need arises  to transform these pictures. 

 
by Dinesh Thakur

Both methods are used in color CRT monitors. Beam penetration method is used for random scan monitors. In beam penetration two layers of phosphor red and green are coated inside CRT screen, the display of color depend on how far electron excites outer red layer, then green layer. This method can produce four colors i.e red ,green, orange, yellow. This is less costly method as compared to shadow mask.

 
by Dinesh Thakur

The most common form of graphics monitor employing a CRT is the raster scan display, based on television technology. In a raster scan system, the electron beam is swept across the screen, one row at a time from top to bottom. As the electron beam moves across each row, the beam intensity is turned on and off to create a pattern of illuminated spots. Picture definition is stored in a memory area called the refresh buffer or frame buffer.



 
by Dinesh Thakur

The various techniques used are:


1) Graphics monitors for the display of three-dimensional scenes have been devised using a technique that reflects a CRT image from a vibrating, flexible mirror. In this system, as the mirror vibrates, it changes focal length.

 
by Dinesh Thakur

1. Optical Touch Panel: Optical touch panels employ a line of infrared light-emitting diodes (LEDs) along one vertical edge and along one horizontal edge of the frame. The opposite vertical and horizontal edges contain light detectors. These detectors are used to record which beams re interrupted when the panel is touched.

 
by Dinesh Thakur

It is a technique to modify or interpret existing pictures, such as photographs. Two principal applications of image processing are:

 
by Dinesh Thakur

Digital Differential Analyzer is a scan conversion line algorithm based on calculating either dy or dx. We sample the line at unit intervals in one coordinate & determine corresponding integer values nearest to the line path for the other coordinate.

 
by Dinesh Thakur

1. Translation: A translation is applied to an object by repositioning it along a straight line path from one coordinate position to another. We translate a 2-D point by adding translation distances tx & ty, to the original coordinate position ( x, y) to move the point to a new position (x? , y?)
X? = x + tx , y? = y + ty.

 
by Dinesh Thakur

Any procedure that identifies those portions of a picture that are either inside or outside of a specified region or space is known as clipping.

 
by Dinesh Thakur

In polygon clipping, we use an algorithm that generates one or more closed areas that are then scan converted for the appropriate area fill. The output of a polygon clipper should be a sequence of vertices that define the clipped polygon boundaries. We can correctly clip a polygon by processing the polygon boundary as whole each window edge.

 
by Dinesh Thakur

There are several techniques that can be used to provide text clipping in a graphics package. The clipping technique used will depend on the methods used to generate characters and the requirements of a particular application.

 
by Dinesh Thakur

Continuous-tone graphs are reproduced for publication in newspapers, magazines & books with a printing process called half toning, & the reproduced pictures are called halftones. For a black and white photograph, each intensity area is reproduced as a series of black circles on white background.

 
by Dinesh Thakur

A surface that is not exposed directly to a light source still will be visible if nearby objects are illuminated. In our basic illumination model, we can set a general level of brightness for a scene. This is a simple way to model the combination of light reflections from various surfaces to produce a uniform illumination called the ambient light, or background light.