Understanding Images on the Computer How do images work and why?

All Images on the Computer work in one of two ways… 1.Vector based images Use math to draw their shapes 2.Raster based images Use pixels to make images

Vector Based Images Tend to be graphic in nature (not photographs) More likely to be made of simple shapes Can be scaled to any size and not get “pixilated” Generally do not create large file sizes

Raster Images Are made up of hundreds or thousands or even millions of little pixels. Used for images hard to describe with math (such as photos) When enlarged they become “pixilated” Have something called “resolution” to define their quality.

Original raster imageBlown up so you can see pixels

About Resolution Measured in DPI (dots per inch) Measured in LPI (lines per inch) Measured in PPI (pixels per inch) Computer monitors generally display at 72 dpi Ink jet printers print at about 150 dpi Laser Printers print at 300 – 600 dpi

Resolution Continued Think about DPI as density of pixels. The more dense they are, the finer the quality of the image. The more pixels there are in an image, the more space that image will take up on your hard disk.

Compression - Lossy JPEG – loses information out of the image to make it smaller. The higher the compression with jpeg, the worse the quality. You will see “artifacts” Files end in.jpg or.jpeg

Compression - Lossless GIF – makes a file smaller by using a kind of short hand to keep track of pixels. Good for graphics without a lot of different colored pixels (not good for photographs) PNG – Like GIF but includes an alpha channel for transparency.

Recommendations Pick the right kind of compression for the job Pay attention to size / quality needs of the situation Don’t let projects get bloated with unnecessarily huge images.