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Vector Art vs. Bitmap

1 years ago 964 Views No comments

This article explores the differences between Vector and Bitmap images.

It's almost impossible to discuss graphic design for stickers or signs without first understanding the differences between the two image formats: bitmap and vector images.

Bitmap Images

Bitmap images (also known as raster images) are made up of tiny pixels. Pixels are essentially small dots that have been assigned a colour. Taken together they form the images that you see on your screen. Most computer monitors display approximately 70 to 100 pixels per inch - the actual number depends on your monitor and screen settings.

Bitmap images are resolution dependent. This means that it is difficult to increase or decrease their size without sacrificing a degree of image quality. When you reduce the size of a bitmap image through your software's resample or resize command, you must throw away pixels. When you increase the size of a bitmap image through your software's resample or resize command, the software has to create new pixels. When creating pixels, the software must estimate the colour values of the new pixels based on the surrounding pixels. This process is called interpolation.

A distinction must be made between resampling and simply zooming in and out, or dragging the edges of your images in a page layout program to resize it. The latter type of resizing is more accurately called scaling. Scaling an image does not effect the image permanently. In other words, it does not change the number of pixels in the image. However, if you scale a bitmap image to a larger size in your page layout software, you are going to see a definite jagged or "pixelated" appearance. Even if you don't see it on your screen, it will be very apparent in the printed image.

Scaling a bitmap image to a smaller size, however, doesn't have any effect; in fact, when you do this you are effectively increasing the ppi of the image so that it will print clearer.

Common bitmap formats include:

  • BMP
  • GIF
  • PNG
  • PICT (Macintosh)
  • PCX
  • TIFF
  • PSD (Adobe Photoshop)

Popular bitmap editing programs are:

  • Microsoft Paint
  • Adobe Photoshop
  • Corel Photo-Paint
  • Corel Paint Shop Pro
  • The GIMP

All scanned images are bitmaps, and all images from digital cameras are bitmaps.

Converting between bitmap formats is generally as simple as opening the image to be converted and using your software's Save As... command to save it in any other bitmap format supported by your software.

Bitmap images in general do not inherently support transparency. A couple of specific formats--namely GIF and PNG -support transparency. In addition, most image editing programs support transparency, but only when the image is saved in the software program's native format. A common misconception is that the transparent areas in an image will remain transparent when an image is saved to another format or copied and pasted into another program. That just doesn't work; however, there are techniques for hiding or blocking out areas in a bitmap that you intend to use in other software.

Vector Images

Vector images are made up of many individual, scalable objects. These objects are defined by mathematical equations rather than pixels, so they always render at the highest quality. Objects may consist of lines, curves, and shapes with editable attributes such as colour, fill, and outline. Changing the attributes of a vector object does not effect the object itself. You can freely change any number of object attributes without destroying the basic object. An object can be modified not only by changing its attributes, but also by shaping and transforming it using nodes and control handles.

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. Fonts are a type of vector object.

Another advantage of vector images is that they're not restricted to a rectangular shape like bitmaps. Vector objects can be placed over other objects, and the object below will show through.

Raster vs vector art

Vector images have many advantages, but the primary disadvantage is that they're unsuitable for producing photo-realistic imagery. Vector images are usually made up of solid areas of colour or gradients, but they cannot depict the continuous subtle tones of a photograph. That's why most of the vector images you see tend to have a cartoon-like appearance. Even so, vector graphics are continually becoming more advanced, and we can do a lot more with vector drawings now than we could a decade ago. Today's vector tools allow you to apply bitmapped textures to objects giving them a photo-realistic appearance, and you can now create soft blends, transparency, and shading that once was difficult to achieve in vector drawing programs.

Vector images primarily originate from software. You can't scan an image and save it as a vector file without using special conversion software. On the other hand, vector images can, quite easily, be converted to bitmaps. This process is called rasterising. When you convert a vector image to a bitmap, you can specify the output resolution of the final bitmap for whatever size you need. It's always important to save a copy of your original vector artwork in its native format before converting it to a bitmap; once it has been converted to a bitmap, the image loses all the wonderful qualities it had in its vector state. If you convert a vector to a bitmap at a size of 100 by 100 pixels and then decide you need the image to be larger, you'll need to go back to the original vector file and export the image again. Also keep in mind that opening a vector image in a bitmap editing program usually destroys the vector qualities of the image and converts it to raster data.

The most common reason for wanting to convert a vector to a bitmap would be for use on the Web. At this time, the most common and accepted format for vector images on the Web is Shockwave Flash (SWF). Another standard for vector images on the Web is SVG, a graphics programming language based on XML. Due to the nature of vector images, they are best converted to GIF or PNG format for use on the Web.

Common vector formats include:

  • AI (Adobe Illustrator)
  • CDR (CorelDRAW)
  • CMX (Corel Exchange)
  • CGM Computer Graphics Metafile
  • DXF AutoCAD
  • WMF Windows Metafile

Popular vector drawing programs are:

  • Adobe Illustrator
  • CorelDRAW<
  • Xara Xtreme
  • Serif DrawPlus