Graphics and Images Graphics and images are both non-textual information, that can be displayed and printed. These images may appear on screen as well as on printers but cannot be displayed with devices only capable of handling characters. The topics discussed are computerized graphics and images, their respective properties, and how they can be acquired, manipulated and output on computers.

Graphics and Images Introduction: Graphics are normally created in graphics application and internally represented as an assemblage of objects such as lines, curves and circles. Attributes of such as style, width and color define the appearance of the graphics. Difference between objects graphics and images Object graphics are composed of can be individually deleted, added, moved or modified later. In contrast, images can be from the real world or virtual and are not editable.

Graphics and Images What is Bitmap (BMP)? The array of pixels (i.e. set of pixels) is called a bit map. In bitmap object based editing is not possible, but image editing tools exist for enhancing and retouching bitmap images. The drawback of bitmaps is that they need much more storage capacity than graphics. Their advantage is that no processing is necessary before displaying them, unlike graphics where the abstract definition must be processed first to produce the bitmap.

Graphics and Images

Graphics and Images (contd…)

Graphics and Images

Portable Bitmap Plus (PBMplus) It is a software package that allows conversion of images between various image formats and their script based modification. PBMplus includes four different image formats PBM – Portable Bitmap for binary images PGM- Portable Graymap for gray-value images PPM – Portable Pixmap for true color images PNM – Portable Anymap for format-independent manipulation of images.

Graphics and Images The contents of PBMplus files are the following:-  A magic number identifying the file type i.e “P1” for PBM.  Blanks, tabs, carriage returns, and the line feeds.  Decimal ASCII characters that define image width.  Decimal ASCII characters that define image height.  ASCII numbers plus blanks that specify the maximum value of color information Filter tools are used to manipulate internal image formats. The functions offered by these tools include color reduction, quantization and analysis of color values etc.

Graphics and Images Bitmap (BMP) BMP files are device independent bitmap files most frequently used in Windows systems. The BMP format is based on the RGB color model. BMP does not compress the original image. The BMP format defines a header and a data region. The header region (BITMAPINFO) contains information about size, color, depth, colortable and compression method. The data region contains the value of each pixel in a line. Lines are flush-extended to a value divisible by 32 and padded with zero values.

Graphics and Images Valid color depth value are 1,4,8 and 24. The BMP format uses the run-length encoding algorithm to compress images with a color depth of 4 or 8 bits/pixel, where two bytes each are handled as an information unit. If the first byte value contains zero and second value is greater than three, then the second value contains number of bytes that follow and contains the color of the next pixel as a reference to the color table (no compression) BMP specifies an additional option to specify a color table to be used to select colors when the image is displayed. BMP specifies an additional option to specify a color table to be used to select colors when the image is displayed.

Creating Graphics Input Devices Modern graphical Input devices include mice, tablets, and transparent, highly sensitive screens, or input devices that allow three- dimensional or higher-dimensional input values. Trackball models are available today that rotate around the vertical axis in addition to the two horizontal axes. A space ball is a solid ball positioned on the elastic base. Pressing or pulling the ball in any direction produces a 3D translation and a 3D orientation. A data glove is a device that senses the hand position and its orientation. It allows positioning objects, exploring and navigating with the scenes, or acting at a distance on the real world. Virtual objects may be manipulated, for example rotated for further examination.

Creating Graphics Graphics software Graphics are generated by use of interactive graphic systems. The conceptual environment of almost all interactive graphic systems is an aggregated view consisting of three software components – application model, application program and graphics system (one hardware component)

Creating Graphics Storing graphics Graphic primitives and their attributes are on a higher image representation level because they are generally not specified in pixel matrix. The higher level has to be mapped to a lower level at one point during image processing, for example when representing an image, having the primitives on a higher level is an advantage because it reduces the data volume that has to be stored for each image allows simpler manipulation. Some graphic packages for example, SRGP (Simple Raster Graphics Package), includes conversion which requires additional step for this conversion which is a drawback, Many color systems uses 8 bits per pixel (eg GIF) so that 256 colors can be represented simultaneously, other formats (including JPEG) allow 24 bits per pixel, representing approximately 16 million colors. Other packages include PHIGS(Programmer’s Hierarchical Interactive Graphics System) and GKS (Graphics Kernel System) use graphics specified by pixmap.

Creating Graphics Graphics storage formats File format for vector graphics allow loading and storing of graphics in vectored representation, such as files created in a vector graphics application. IGES: The initial graphics Exchange Standard was developed by an industry committee to formulate a standard for the transfer of 2D and 3D CAD data. DXF: Autodesk’s 2D and 3D format was initially developed for AutoCAD a computer aided design application. HPGL: The Hewlett Packard Graphics Language has been designed to address plotters, which is the reason why it only supports 2D representation. The combination of vector and raster graphics is generally possible in modern vector graphics systems. Only few so called meta files such as CGM- Computer Graphics Meta file, WMF (Windows Meta File) and others allow an arbitrary mixture of vector and raster graphics