Understanding Images on the Computer How do images work and why? All Images on the Computer work in one of two ways… 1.

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Transcript Understanding Images on the Computer How do images work and why? All Images on the Computer work in one of two ways… 1.

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 image
Blown 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.