File Sizes & Types

Size Matters

Kilobytes (K)• 1024 bytes = 1 kilobyte—

a tiny trademark graphic or log might be a few kilobytes in size, whereas a full web page might be 35-100 kilobytes. Anything beyond 100K will probably require significant download times for people with dialup modems. Word docs are usually under 1000K, even with images.

10K

Megabytes (MB)

(This PPT presentation is just under 1MB)

• 1024KB = 1MB (megabyte)—Most email servers have maximum of 2MB you can send. PowerPoint presentations get this big because of images. About 10-20 web pages would take up 1MB. Web hosting sites sell server space in terms of megabytes. My web site has more than 2000 files, and I have still not reached my 150 MB capacity (but we’re getting close).

Gigabytes (GB)

• 1024MB = 1GB (gigabyte). Rarely do we see single files that are in the gigabyte range. Usually you will see the term gigabyte to indicate hard drive space.

Terabytes

• 1024GB = Terabyte

File Formats

Common For Web

• JPEG GIF

Original .jpg dithered .jpg gif 8 colors

gif 4 colors

“When Good PhotosGet Saved Badly”

How should this

have been saved:jpg or gif?

How was it saved

instead?

Extension Format Used for `Loss `# Colors Transparency?

.jpgJointPhotographicExperts Group

Continuoustone (e.g.,photos) Web

Lossy ThousandsNO

.gifGraphicInterchangeFormat (Compuserve)

Solid colors(e.g., cartoons)

Web

Lossless

256 + transparency

Yes, GIF-8 (jaggies)

.pngPortableNetworkGraphicsformat

Web(continuoustone or solidcolors)

LosslessThousands

Yes (no jaggieds)but big file

.tifTagged ImageFile Format

Print Only Lossless Thousands Yes

File Formats

Transparency: gifs & pngs for web

“The dreaded white jaggies”

White jaggies are undetectable on white background, but that defeats the purpose of transparency for use with any colored background.

Solution: Use a 24-bit png

Quiz Yourself:How would you save this?

• Photo of your sister on the web

• Black and White logo on the web without transparency

• Black and white logo with transparency

• Image for National Geographic

Compression

• Zip files

• Jpegs

• Tifs

• Compress ONCE

• Cannot uncompress Jpegs and Gifs or add quality that is lost.

Dots Per Inch (dpi)• 72 dpi standard for web

• 85-150 dpi low quality print

• 200 dpi starting point for decent print

• 300 dpi pretty strong

• Goes up to 2,000 dpi for highest quality on average scanners (creates enormous files)

Questions?