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JPEG image compression FAQ, part 1/2

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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?


[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
(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.

User Contributions:

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Oct 28, 2014 @ 6:06 am
sdsfsdfsd fsdf sdfsd fsd fsd fsd fsdfsdf sdf sdfsd fsdf sd fafsd fsa f
David Avs
Report this comment as inappropriate
Oct 28, 2014 @ 5:17 pm
Progressive JPEG is supported by all modern browsers.

There are libraries and even online tools to automatically convert JPEG files from progressive to baseline and back. For example, Uploadcare uses URL commands to do that:

* JPEG - Progressive: 6fdab0d5-5a07-4b34-8a3a-f61727972745/-/format/jpeg/-/progressive/yes/
* Same JPEG, Baseline: 6fdab0d5-5a07-4b34-8a3a-f61727972745/-/format/jpeg/-/progressive/no/

Here is how it looks in action (when first loaded, you can see how each image starts appearing differently):

See more docs at Uploadcare website.

Comment about this article, ask questions, or add new information about this topic:


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Last Update March 27 2014 @ 02:11 PM