Everything we read either book or web pages are documents made of 2 things i.e., Text and Graphics.
a) When we look around we find many graphics software such as Corel Draw, Photo shop, AutoCAD, Snag it and many more. Why do we need so many software for generating Images / Drawings?
b) When I look at any Magazine or Hoarding I see the Graphics Quality is very nice but when I put images in word and stretch them, why the Quality Diminishes?
c) How Quality of Print is measured? Or What is the Meaning of DPI?
Many Questions come to users mind when working with Graphic Files.
Understanding difference between Vector, Raster and Hybrid Graphics helps them to address these Questions.
What is a Raster Image?
A raster image is collection of various square or rectangle shaped color boxes (array of dots) called pixels. Each Pixel square (or rectangle) is described as black, white, gray or any color in a Raster image. Let it be Text, Line, Circle or Arc, all will be represented by coloring the appropriate pixels.
When you scan a drawing, take a photograph with a digital camera or create an image in paint, we get Raster Images.
Raster images can be saved as various sorts of file formats including BMP, CALS, GIF, IMG, JPEG, PCX, PDF, PNG and TIFF.
What is a vector image?
A vector image is made up of mathematically defined entities identified by coordinates. CAD programs such as AutoCAD and other vector-based software like Corel Draw create vector images.
Vector image file types include DXF, DWG, DGN, HPGL, SVG, EMF, WMF and PDF.
Advantages of Raster Images
a) Since each pixel can be given a different color, it helps in creating graphically appealing output
b) It is comparatively easy to create Raster Images.
Limitations of Raster Images
a) You will notice the difference in clarity when you scale (magnify) the Raster Image.
b) It is more difficult to edit Raster Images
Some of the Raster Image Applications
Most of the Artworks that gets printed will be Raster Image. Let it be Advertisement, Photos, and Graphic Images that you see in web pages, or a Globe that you see in Google Map / Earth will all be raster images.
Adobe Photoshop is one of the most popularly used Raster Image Editors.
Advantages of Vector Images
a) Vector Graphics Quality is not affected by scaling (enlarging or reducing their size). Because vector elements are mathematically defined, scaling simply requires modification of their mathematical locations.
b) Comparatively it is easy to edit Vector Graphics
Limitations of Vector Images
a) It is very difficult to create attractive images with special effects using Vector Graphics.
b) It is impractical to create photographs (Image having many details) in Vector Graphics.
Some Vector Graphics Applications
a) Logo design: Creating a vector logo is more difficult but the effort pays for itself when the vector logo file is sent to printers or sign makers etc. The vector logo can be scaled up or down with out losing quality and would enable smooth transition between various media. Corel draw, Inkscape, Illustrator are some of the software’s used for creating Vector Graphics for presentation purpose.
b) Engineering Drawing: All engineering drawings will be based on coordinates (mathematics) and hence software like AutoCAD, MicroStation are used for producing Engineering Drawing.
Printing Graphics and Printing Quality Measurement:
It is important to note that printers can only recognize Raster image. Although the graphics is created in Vector Graphics, when it goes for printing it will be converted to Raster image as printing technology converts the image in to dots and prints. Quality of print will be better when the printer is capable of printing higher resolution image. Unit of measurement for Quality of printing is DPI (Dots per inch).
Raster to Vector Conversion:
It is comparatively easy to convert a Vector image into Raster image. Whereas, converting a Raster image back to vector file is not an easy process. There are many commercial applications developed to convert raster images back to Vector images but fail to convert raster to vector in many cases.
You will probably be able to load a raster image into your CAD program - most CAD programs can import and display raster images. Once you have imported a raster image into your CAD program you will be able scale the image, rotate the image but you will not be able to access each entity as you do with other entities of your CAD Program. You must either redraw the raster image manually using your CAD program or a dedicated redrawing program or a raster to vector program if you wish to work with individual entities.
Since both Graphics types have advantages and limitations, most of the Graphics software now offer the capability to handle both Vector and Raster Graphics.
Understanding these Raster and Vector Image properties and limitations always helps us when working with Graphic Files.