Lecture: Understanding Format Choice and Image Compression

Lecture: Understanding Format Choice and Image Compression

File Formats

• All files have different formats, determined from their origin.
• Files such as photo and video can be reduced in size by using image compression formats.

Lossy vs. Lossless

• Graphic image formats fall under two categories of compression, Lossy or Lossless.
• Lossy image data is “lost” or reduced for smaller file size, this can cause poor image quality. Can result in showing “compression artifacts.”
• Lossless retains image data for higher quality, but larger file sizes.

Graphic Formats

• TIF, JPG and GIF are three most common formats for activities such as printing, scanning and displaying images over the internet.
• PNG is common web format, is high quality and can contain an alpha (transparency) channel.
• Each format has its own advantages and disadvantages.

TIF

• Stands for Tagged Image Format
• Common format for desktop publishing, print, photo and graphic design.
• Is a Lossless file format. It retains image data for maximum image quality.

JPG

• Stands for Joint Photographers Expert Group.
• Created for digital photography and works best for photo content.
• Is a Lossy format.
• Can reduce image file size by 10:1 without showing significant compression.  

GIF

• Stands for Graphics Interchange Format
• Best for graphics or images that have flat color or even tone, such as a cartoon.
• Reduces image size by “indexing” color from 3 channels to 1
• Is adjustable by changing color bit levels from 1 to 8
• Contains no DPI (Dots Per Inch) data for printing. Not good format for printing.

Know Your Pixels

• TIF and JPG are best for images with pixels that blend in color, these are called  “contiguous pixels.”