Graphic File Formats Notes

Graphic File Formats

·      All documents/files are packaged in a different format; much of the time it is determined by the software of the file’s origin (i.e. PS, ID).

·      File size can be reduced with compressions, but this can potentially affect the look of the file.

·      Lossy Compression: Image data is “lost” to reduce file size and can cause poor quality (results in compression artifacts – pixilation) – vs. – Lossless Compression: Retains all data resulting in a large file with a higher quality.

·      TIF (best for printing), JPG, and GIF are the most common formats for common actions (printing, scanning, web). PNG is a common web format that has high quality as well as an alpha (transparency) channel.

TIF – Tagged Image Format

·      Common format for desktop publishing, print, photo, graphic design.

·      Lossless file format: retains image data and original quality.

·      Large file size that is not internet-friendly/browser-compatible

JPG – Joint Photographers Expert Group

·      Created for digital photography and is best used for photos.

·      Lossy file format, however can reduce file size by 10:1 without showing significant artifacts. Level of compression is adjustable.

·      Continuously resaving (and thus compressing) JPGs results in loss of quality. Try not to recompress files; instead, return to the original.

·      “Banding” occurs with contiguously changing colors.

GIF – Graphics Interchange Format

·      Best format for graphics that have flat color or tone (i.e. cartoons).

·      Reduces image size by “indexing” color from channels to 1.  Is adjustable by changing color bit levels from 1 to 8.

·      Contains no DPI (dots per inch) data for printing.

·      Can contain movement.

·      Cinemographs

For best quality – TIF or PNG (lossless compression and no JPG artifacts)

Smallest file size – JPG with a higher quality factor  for photographic images and TIFLZW or GIF or PNG for graphics.

Pixels

·      TIF and JPG are best for images that blend, called contiguous pixels.

·      GIF is best for images with flat, even tones, or non-contiguous pixels.

Alias vs. Anti-Aliase

·      Aliased images have hard, jagged images. Anti-aliasing smooths out edge pixels to create a smooth transition.

·      Can be seen in Photoshop when zooming in and fixed with various tools.

·      Aliased art (i.e. pixel art) is also used.