The JPEG Online Laboratory

Notes:

• This tool can be regarded as Web-based Front End to the jpegtran utility for lossless JPEG transcoding from the Independent JPEG Group. This means that all transformations performed by this tool retain the original image contents, with no further quality loss! Only reversible image transformations are performed.

• This tool utilizes the "Form-based File Upload in HTML" feature, defined in RFC 1867. Thus, you need an up-to-date Browser version (e.g. Netscape 3 or newer) which supports that standard. Otherwise, you can't choose a local file for upload in the above input field.

• This tool provides a rather novel operating mode: The Server-side CGI program which receives the posted data from the client will send the transformed data immediately back to you as 'raw' image, within the same HTTP request-response cycle! This approach has several advantages:

  • No file storage or other permanent resources are required on the Server.
  • Only one single (CGI) process per request is required as Server resource, no further processes need to be spawned since all code is built in a single compiled C program.
  • No problems with concurrent client requests. Simultaneous accessibility is limited only by Server configuration for CGI processing.
  • Maximum efficiency with minimum transfer, storage and processing overhead.

  Thus, this tool acts somewhat similar over the net like filter programs on a UNIX system (using pipes), with the difference that all source data has to be swallowed before the first output data can be emitted.

  Since the returned image does not have a unique URL, you must explicitely save the image per Browser menu if desired.

• Unfortunately, there are some unsolved problems regarding the client cache behaviour. You have to reload the image and confirm the "repost form data" dialog after subsequent operations. This is odd. Any suggestions to solve this problem are greatly appreciated!

• Send me your questions, hints, feature requests etc.! Have fun...