There is no issue with the RFC 2435 Appendix A neither with the live555 procedure to scale a quantization table with a Q factor. Both are correct.. If you read the header of Appendix A it clearly states the reason of the example code : "The following code can be used to create a quantization table from a Q factor..." Now when you recompute the quantization table from a selected Q factor your only scale the 64 quantization values by the same factor. Doing the procedure on zigzag order on doing it on "standard" non-zigzag order doesn't matter. It will yield the same "scaled quantization factor".
Jpeg encoding/decoding of spectral component of the picture operate on block of 64 values. Those value must be processed in zigzag order. If you use a zigzaged table then the encoding/decoding only increment the index of the quantization value in the table to get the good quantization value. However if you use a non-zigzag table then the encoding/decoding must find and pick-up the good quantization inside the table. This is up to the implementation of the code. Guy Bonneau From: Alexandr Němec <a.ne...@atlas.cz> To: LIVE555 Streaming Media - development & use <live-de...@ns.live555.com>, Date: 2013-11-25 07:06 Subject: Re: [Live-devel] RFC 2435 compliance Sent by: live-devel-boun...@ns.live555.com > This same question (I think) came up last January. Here is the answer that I gave at that time: Thanks for your quick reply. Sorry, I googled through the archives, but did not find this one. The "zigzag" idea is the correct answer, as this order is required for the JPEG DQT segment. So Live555 is absolutely correct here, but it turns out, that the code in Appendix A of RFC 2435 omits to use the reordered tables when creating jpeg headers, ie. it contains a bug. I just could not believe that a RFC code example can contain a bug. Thanks. Best regards Alex _______________________________________________ live-devel mailing list live-devel@lists.live555.com http://lists.live555.com/mailman/listinfo/live-devel DISCLAIMER: Privileged and/or Confidential information may be contained in this message. If you are not the addressee of this message, you may not copy, use or deliver this message to anyone. In such event, you should destroy the message and kindly notify the sender by reply e-mail. It is understood that opinions or conclusions that do not relate to the official business of the company are neither given nor endorsed by the company. Thank You.
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