Notes - Graphic File Formats [9/18/13]

Overview

• All computer documents/files are packaged in different formats.
• The format is often determined by the file's origin, such as a software program like Photoshop.

Lossy v Lossless

• Graphic image formats fall under these 2 categories.
• With Lossy, the image data is "lost" or reduced for smaller file sizes but can cause poor image quality. Can result in showing "compression artifacts", such as pixellation or banding.
• Lossless retains image data for higher quality, but larger file sizes.

Graphic Formats

• TIF, JPG and GIF are the 3 most common formats for common activities such as printing, scanning and displaying images over the internet.
• PNG is a common web format, is high quality and can contain an alpha (transparency) channel.
• Each format has its own advantages and disadvantages.

File Format: 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.
• Can result in larger file sizes, not fit for display over internet, is not browser compatible.

File Format: JPG

• Stands for Joint Photographers Expert Group.
• Created for digital photography and works best for photo content.
• Is a LOSSY format.
• Can reduce and image file size by 10:1 without showing significant compression artifacts.
• The level of compression is adjustable.
• Nonetheless, it can leave many compression artifacts.
• Better for files that contain flat colors.
• Do NOT re-compress JPG files.

File Format: GIF

• Stands for Graphics Interchange Format.
• Is 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 a proper format for print.
• Can have multiple frames for animation.
• Referred to as a "cinemagraph". It creates loops of animations.

Know Your Pixels

• TIF and JPG are best for images with pixels that blend in color, these are called "contiguous pixels".
• GIF is best fir images with flat even tune, or "not contiguous pixels".
• Aliased pixels have a hard edge which is not smoothed out. "Jaggies"
• Anti-Aliased pixels are smoothed out into many different tones of a color.

Lowest to Highest Quality