Question

Identify the effects of enlarging vector and bit-mapped images in relation to file size and quality. IT110

Answer 1

Because bitmaps are resolution dependent, it's impossible to increase or decrease their size without sacrificing a degree of image quality.

When you increase the size of a bitmap image, the software has to create new pixels. When creating pixels, the software has to estimate the color values of the new pixels based on the surrounding pixels. This process is called interpolation.

Let's assume you have a red pixel and a blue pixel beside each other. If you double the resolution you will be adding two pixels between them. Interpolation is the decision process that determines which color those added pixels will be; the computer is adding what it thinks are the correct colors.

Scaling an image does not affect the image permanently. In other words, it doesn't change the number of pixels in the image. What it does is make them bigger. However, if you scale a bitmap image to a larger size in your page layout software, you're going to see a definite jagged 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 doesn't have any effect. In fact, when you do this you're effectively increasing the PPI of the image so that it will print clearer. This happens because it still has the same number of pixels but in a smaller area.

Unlike bitmaps, vector images are not based on pixel patterns, but instead use mathematical formulas to draw lines and curves that can be combined to create an image from geometric objects such as circles and polygons. Vector images are edited by manipulating the lines and curves that make up the image using a program such as Adobe Illustrator.

Vector images have some important advantages over bitmap images. Vector images tend to be smaller than bitmap images. That’s because a bitmap image has to store color information for each individual pixel that forms the image. A vector image just has to store the mathematical formulas that make up the image, which take up less space.

Vector images are also more scalable than bitmap images. When a bitmap image is scaled up you begin to see the individual pixels that make up the image. This is most noticeable in the edges of the image. There are ways of making these jagged edges less noticeable but this often results in making the image blurry as well. When a vector image is scaled up, the image is redrawn using the mathematical formula, so the resulting image is just as smooth as the original.