There are two major types of 2D graphics used by designers: raster (or bitmap) and vector images. Each graphic type has distinct characteristics that are important to understand when doing graphic design work.
Vector images are composed of paths creating individual, scalable objects. These objects are defined by mathematical equations to render high quality graphics. Vector graphics consist of lines, curves, and shapes with editable attributes such as color, fill, and outline.
Vector-based Images Are Resolution Independent
Changing the attributes of a vector graphic does not affect the graphic itself. You can change any number of the graphic attributes without destroying the basic image. Because they’re scalable, vector-based images are resolution independent. You can increase and decrease the size of vector images to any degree and your lines will remain crisp and sharp, both on screen and in print.
When To Use Vector Images
Wherever possible use the vector format for all your type, line art and illustrations. Vector images are very useful when developing something for scale or sending to a printing company and are ideal for logo design and illustration. A disadvantage is that vector images are unsuitable for producing photo-realistic imagery.
Vector File Formats
Common vector file formats include:
- AI (Adobe Illustrator)
- CDR (CorelDRAW)
- EPS (Encapsulated PostScript)
- WMF (Windows Metafile)
- DXF (AutoCAD)
- SVG (Scalable Vector Graphics)
Popular Vector-Based Drawing Programs
- Adobe Illustrator
- Serif DrawPlus
- Xara Xtreme
Raster images are also commonly known as bitmaps and are composed of pixels in a grid. Pixels are tiny dots with an assigned color value. These dots of color come together to form the images you see. When increasing the size of a raster image the pixels defining the image can be increased in either number or size. The image will begin to lose detail and clarity when the pixels are spread over a larger area. Scanned graphics and web graphics are the most common forms of raster images.
Raster-based Images Are Resolution Dependent
The resolution of an image is usually stated in dpi (dots per inch) or ppi (pixels per inch). Raster images are displayed on your computer screen at approximately 100 ppi. When printing raster images, your printer needs much more image data than a monitor. To render a bitmap image accurately, the typical desktop printer needs 300-600 dpi. The quality of the print increases when a higher resolution is used.
Bitmaps cannot be scaled without the loss of quality to the image. Because raster images are resolution dependent, it’s difficult to increase or decrease their size without sacrificing the overall quality. The image may appear clear on screen, but once printed the loss of quality is more apparent as the image may appear pixelated or blurry.
When To Use Raster Images
Raster images are best used for photographs and images with subtle shading. This graphic type is useful when editing, manipulating, or adding special effects to an image. Raster images should not be used when transparent backgrounds are preferred or on images where high quality needs to be maintained once the image is scaled.
Raster File Formats
Common raster file formats include:
- BMP (Windows Bitmap)
- JPEG, JPG (Joint Photographics Expert Group)
- GIF (Graphics Interchange Format)
- TIFF (Tag Interleave Format)
- PNG (Portable Network Graphic)
- PCX (Paintbrush)
- PSD (Adobe PhotoShop)
- CPT (Corel PhotoPAINT)
Popular Bitmap Editing Programs
- Adobe Photoshop
- Microsoft Paint
- Corel PhotoPAINT
Both vector and raster images have distinct purposes when used in graphic design. Understanding when to use each graphic type will aid a designer in becoming more efficient in their work.