[theora] Theora Intra (ptalarbvorm) vs. MJPEG

Basil Mohamed Gohar abu_hurayrah at hidayahonline.org
Wed May 12 21:14:33 PDT 2010

On 05/12/2010 03:27 PM, Andrey Filippov wrote:
>     I see a lot of sense in these assertions.  However, what pops-up to me
>     for a regular user is that it's an additional step they have to take,
>     and most tools don't already feature this capability.  It seems
>     that, if
>     we incorporate such a codec into the resulting product, then we will
>     have to also have software ready for the consumer to use to do the
>     post-processing.
> Yes, sure it needs software to process. But there are multiple ways
> how to make it seamless.
>     I'm looking at the page now.  It's very interesting...
> That page was designed to be a supplement to the article
> http://www.linuxfordevices.com/c/a/Linux-For-Devices-Articles/Elphel-camera-under-the-hood-from-Verilog-to-PHP/
> , but during some site re-design the articles got javascript corrupted
> Here is a link to ImageJ plugin for JP46. Additionally it reads Exif
> MakerNote field and un-applies gamma and analog gains, so ImageJ gets
> floating point pixel data proportional to the number of photons the
> sensor actually detected:
> http://elphel.git.sourceforge.net/git/gitweb.cgi?p=elphel/ImageJ-Elphel;a=summary
>     > So far most JP46 images were used for still images (with Elphel
>     model
>     > 323 and 353 cameras) but now we at least some solutions for the
>     video
>     > and continue to work in this direction. And there could be
>     > alternatives to literal JP4 implementation
>     I did see some video samples of the JP46 video, but I don't think
>     I saw
>     the resulting demosaiced video.
> There are several here and there - made by ourselves (i.e.
> http://community.elphel.com/videos/2010%2003.19-21%20CanyonLands/canyonlands_clip01.avi),
> but you can find much more processed stills made by others.
>     It would be great if we had some raw Bayer video footage.  I don't
>     have
>     any right now...can anyone point us to some?  It would also be nice if
>     JP46 was available as an actual codec to use for "compressing" the raw
>     Bayer video as well.  Supposedly my webcam (Logitech Webcam C600) has
>     the ability to send raw Bayer pixel data, but I don't know in what
>     format that is.
> Yes, it could be applicable to other cameras too - JP4 is basically
> JPEG with different color components and pixels rearranged for optimal
> compression of Bayer data. Funny thing that I am not aware of any
> software JP4/JP46 encoder - from the very beginning it ran in the
> hardware
> (http://elphel.cvs.sourceforge.net/viewvc/elphel/elphel353-8.0/fpga/x3x3/)
> - modified from the regular color 4:2:0 JPEG I implemented earlier.
> And there are multiple software decoders.
> Andrey
> PS. We do have cameras available for developers
> (http://wiki.elphel.com/index.php?title=Pricing/Discount/Donation_Policy )
I was thinking more about the JP4 codec, and I realized that all the
data could be contained in a single luma channel for JPEG or Theora. 
Why, then, the need for the empty chroma channels in the case of JP4,
because regular JPEG supports a grayscale mode that is just luma data. 
The same goes for Theora, and that is what I think we should jump
straight into if we're going to use such an encoding scheme.  Am I
missing something?  Is this basically what the MJP4 format is?

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