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What is Raster Graphics

Updated on October 1, 2010

Raster graphics and images are most frequently used. These are created by a series of hundreds and thousands of minute dots that collectively make a bigger image. One can compare raster images with a montage which is constituted by a series of smaller images

Raster graphics are typically used for complex images formed from lots of different colors and shapes, most notably photos.

In general, raster graphics are used for multifarious images produced by assortment of diverse shapes and colors. These images are great for rendering rich, full-color images  photographs and photo-realistic images. 

Developing and editing an image which is made of dots facilitates rich detail in any image for the reason that each dot can be colored from a variety of colors present in the color palette and one can chose any color one desires.

To get a clear idea on how raster graphics work let’s consider some everyday examples:

  • If you have a look at your pc screen you would notice that all the text and graphics is formed by a number of tiny graphic elements called pixels.
  • Similarly, the printed pages from a facsimile machine or a printing device are formed by a string of minute dots.
  • A more lucid example is a photograph taken from a digital camera. When the photo is clicked, it is saved in the camera memory in the form of a sequence of bits of information constituting minute colored dots in a grid.


Raster Images and RGB colors

Every pixel or dot has a consequent red, green, and blue value that come together to influence the color displayed by that pixel. According to this, distinctive raster graphics and images generally function in the RGB color. The RGB color is the bare format that a PC graphic hardware uses to display any image on the PC screen, in addition to this; it is the foundation for numerous graphic file formats.

RGB Raster Image
RGB Raster Image

Let’s assume the smiley at the top left corner is an RGB raster image. When zoomed in, it would look like the big smiley face to the right. Every square or dot corresponds to a pixel. If we further zoom or enlarge the image, we see three pixels whose colors are constructed by adding the values for red, green and blue.

A colored raster image will usually have pixels with between one and eight bits for each of the red, green, and blue components, however other color encodings are also employed, such as 4- or 8-bit indexed representations that apply vector quantization on the (R, G, B) vectors. The green component sometimes has more bits that the other two to furnish to the human eye's better discrimination in this component.

Original Image
Original Image
Zoomed Image Shows pixels or dots and quality of image is reduced.
Zoomed Image Shows pixels or dots and quality of image is reduced.

Limitations of Raster Graphics

Size Dependent

Raster graphics are size-dependent which means these images do not resize well which is one of its major drawbacks.

Generally the dots or pixels are very minute which makes it appear that these dots are blended and give the impression of being one continuous image but when we try to print these images at a size larger than what the file was created, at certain point we will be able to notice individual portions as blocks or square dots making the image look like distorted and blurry or grainy.

In the same way if we try to make image smaller than it was intended then we may face some problems.

For instance, if a line which is two dots thick; is attempted to be printed at less than half of its original size then it can disappear entirely since the printer will not be able to publish something which is smaller than one dot.

Uses Large File Size

One more drawback is that high resolution raster images have large file size which would require more PC memory and may cause slower editing.

For example, lets take a 1 inch x 1 inch square, if we create this square at 300 dots per inch (dpi) subsequently this square will have 300 dots per pixels in it, because of this the PC must keep a record of all the zeros and ones that constitute those 300 dots per pixels which directly means the image will have a larger file size.

How to deal with a raster image that may require enlarging and printing in future?

One straightforward solution is to make sure the image is created in high resolution, (at a minimum of 300 dots per inch (dpi) will resize quite well and maintain reasonably good precision, nevertheless, it will only enlarge so much. If you want to have flexibility to scale and enlarge images then you should create a vector based image.

How to edit a Raster Image?

Raster graphics can be easily edited by using image editing softwares which facilitates the user to paint and edit images or graphics interactively on the computer screen and enable to save these in a variety of “raster” or “bitmap” formats with file extensions like .TIF, .JPG, .GIF and .BMP

Image editors such as GIMP, Adobe Photoshop, Corel Photo Paint, Ms Paint etc are raster-based image editors which allow precise editing and provide total freedom in image appearance. Comprehensive list of raster based photo editors is as follows:

Open Source photo editors:

  • DigiKam
  • Gimp
  • Krita
  • Pinta
  • KolourPaint
  • Tux Paint
  • GrafX2

Commercial Photo Editors:

  • Adobe Photoshop
  • Adobe Photoshop Elements
  • Corel Painter
  • Corel Painter Essentials
  • Corel Paint Shop Pro
  • Corel Photo-Paint
  • Corel PhotoImpact
  • Pixel Image Editor
  • PhotoPerfect
  • Pixelmator
  • RealWorld Photos
  • TVPaint

Freeware Photo Editors:

  • Artweaver
  • Pixia
  • Paint.NET
  • IrfanView

Comments

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    • Vector design profile image

      Saim 

      5 years ago from California

      Hello FuzzyCookie,

      You write very well. i really like this hub and its useful for me to learn some new points.I am also working on logo and vector designs. As i know Raster graphic and vector graphics are most important in graphic designing.

    • profile image

      JAHO 

      6 years ago

      great work keep it up

    • FuzzyCookie profile imageAUTHOR

      FuzzyCookie 

      8 years ago

      Hi Timothy, I am glad that this info has helped you in some way and thanks for adding it in your hub. Cheers!

    • timothy82rodrigu profile image

      timothy82rodrigu 

      8 years ago

      Great images to help explain raster graphics (and why they're not always appropriate). I found this Hub doing a quick search for explanations of raster images. I've added a link to your page from my Hub about logo design.

      Great resource! Keep up the good work!

    • FuzzyCookie profile imageAUTHOR

      FuzzyCookie 

      8 years ago

      Hello cutesygirl, thank you for your kind comments. I am currently working on the Vector images hub :D

    • cutesygirl profile image

      cutesygirl 

      8 years ago

      Great article, useful for people wondering why their image gets distorted when they try to blow it up. I personally used Gimp to edit raster.

      Have you thought about doing a "What is a Vector Image"? You could use the pricey Adobe Illustrator, or you can use the opensource program, Inkscape.

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