This article answers Frequently Asked Questions about JPEG image compression.
This is part 1, covering general questions and answers about JPEG.  Part 2
gives system-specific hints and program recommendations.  As always,
suggestions for improvement of this FAQ are welcome.

New since version of 14 March 1999:
  * Expanded item 10 to discuss lossless rotation and cropping of JPEGs.


This article includes the following sections:

Basic questions:

[1] What is JPEG?
[2] Why use JPEG?
[3] When should I use JPEG, and when should I stick with GIF?
[4] How well does JPEG compress images?
[5] What are good "quality" settings for JPEG?
[6] Where can I get JPEG software?
[7] How do I view JPEG images posted on Usenet?

More advanced questions:

[8] What is color quantization?
[9] What are some rules of thumb for converting GIF images to JPEG?
[10] Does loss accumulate with repeated compression/decompression?
[11] What is progressive JPEG?
[12] Can I make a transparent JPEG?
[13] Isn't there a lossless JPEG?
[14] Why all the argument about file formats?
[15] How do I recognize which file format I have, and what do I do about it?
[16] What other common compatibility problems are there?
[17] How does JPEG work?
[18] What about arithmetic coding?
[19] Could an FPU speed up JPEG?  How about a DSP chip?
[20] Isn't there an M-JPEG standard for motion pictures?
[21] What if I need more than 8-bit precision?
[22] How can my program extract image dimensions from a JPEG file?

Miscellaneous:

[23] Where can I learn about using images on the World Wide Web?
[24] Where are FAQ lists archived?


This article and its companion are posted every 2 weeks.  If you can't find
part 2, you can get it from the  archive at rtfm.mit.edu
(see "[24] Where are FAQ lists archived?").  Part 2 changes very frequently;
get a new copy if the one you are reading is more than a couple months old.