Raster vs Vector

In this article we are going to discuss some basic knowledge of the two major graphical image types: Raster (often called Bitmap) and other being vector. We will also have a look at the software used to create them and there associated file types. Such knowledge will greatly enhance your finished artwork before sending to a commercial printer.

Raster

When you scan an image or take a photograph a raster image is produced. Raster or bitmap images are made of small pixels or bits inside a grid to form an image. Each pixel or bit contains information about the image colour to be displayed.

A raster image.  When zoomed in you can see its made of little 'block's called pixels
A raster image. When zoomed in you can see its made of little ‘block’s called pixels

The downfalls of raster images

  1. The file size of bitmap images are often quite large as the computer stores information about every single pixel of that image.
  2. The other downfall of raster images is that when you enlarge the image you lose quality and produce a more pixelated result.
Original photo (raster) image.  Looks fine.
Original photo (raster) image. Looks fine.
Image now enlarged.  You can see the image is very'pixelated' or blurry
Image now enlarged. You can see the image is very’pixelated’ or blurry

Raster image software

The most famous graphical software used to create raster images are the following:

  • Photoshop
  • GIMP

These advanced software programs are able to save the raster image in a variety of file formats:

  • JPG
  • PNG
  • GIF
  • TIFF

Resolution

The resolution is the image size of often expressed in the number of pixels wide by the number of pixels high. Take a look at your camera settings you will see a variety of different resolutions.

Typical camera resolutions with associated file sizes
Typical camera resolutions with associated file sizes
In the picture the ‘Large’ size is 6000 pixels wide by 4000 pixels high. This file size would be 24MB.

Display Monitors

The size of a display monitor has a resolution also eg. 1920 pixels wide by 1080 pixels high. Taking the large sized photo ie (6000px by 4000px) and displaying it on the screen would mean it would be much too large for it to be seen in its entirety ie at 100%. It would have to be reduced by more than a third.

Printing considerations

Things behave differently in the print world. Another factor comes into play, namely the dpi (dots per inch), sometimes known as ppi (pixels per inch). Both in-house printers and commercial printers print ‘dots’ of ink onto paper. The standard in the commercial print world is 300dpi. So, if you’re going to print your photo then you need to divide its width and height in pixels by 300 to get the dimensions of the final print in inches.

So, the photo at 6000px by 4000px would be 6000/300 = 20″ wide by 4000/300 = 13.33″ in height.

Vector

Vector images unlike raster images are lines and shapes based on mathematical calculations.

The advantage of using vectors

As we mentioned earlier in this article, raster images become distorted when enlarged. This is not the case with vector images; they look exactly the same at any size.

The disadvantages of using vectors

Because vectors are based on mathematical calculations producing lines and shapes they cannot be used for realistic images like photos. Even if you tried to emulate a realistic type photo using vectors the result would be an extremely large file.

Vector image software

The most famous and widely used vector software are:

  • Adobe Illustrator
  • Corel Draw
  • Adobe Photoshop can use both vector and raster images

These advanced software programs are able to save the vector image in a variety of file formats:

  • ai
  • eps
  • cdr

I hope this short article clarifies the distinction between raster and vector images, when to use them, when not to use them and the software used to produce them.

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