[IGSTK-Developers] Tcon minutes March 29, 2007

[Frank Lindseth]

On Apr 2, 2007, at 10:51 PM, Luis Ibanez wrote:

>
>
> Hi David,
>
>
>             Yeap, an experiment confirms that I'm wrong.
>
>
> I just ran a profile of the time that it takes to convert YUV to RGB
> using the code that you contributed to the vtkWin32VideoSource.cxx .
>
> For the same machine of my previous email, and an image of 1024 x  
> 768 pixels
> the timing is:
>
>                                           32 milliseconds.
>
>
> Attached is the code that I used for profiling the conversion.
>
> That code produced the following output:
>
>
> Probe Tag    Starts    Stops           Time
> Conversion     1         1         0.0319588
> FillBuffer     1         1         0.00697708
>
>
>
>
> I would insist however in that any discussion related to performance
> must be based on numbers that we have measured using repeatable
> experiments. Otherwise we will start looking like reviewers of  
> decadent
> Journals.
Thanks for the update Luis and David.
Point taken Luis, we agree 100% that a decision should be taken based  
on figures/facts whenever possible.
Still, I'm hoping that a discussion can be raised/started without  
having all the hard data on the table (what an how to measure
could be one of the points discussed....).

- Frank

>
>
>
>     Regards,
>
>
>          Luis
>
>
> ---------------------------------------------------------------------- 
> -------------
> On 4/2/07, David Gobbi <dgobbi at atamai.com> wrote:
> Hi Luis,
>
> I missed the T-con last Thursday, so I might be a little bit
> out-of-context, but the cost of the color conversion will vary
> quite a bit depending on exactly which conversion is being
> done (as well as on how the conversion code is optimized).
>
> The most expensive conversions are from YUV to RGB and
> back again, since they essentially require a 3x3 matrix multiplication
> plus 3 clamp operations per pixel.   Also, these conversions
> are lossy in both directions.
>
> Conversion from greyscale to YUV or RGB is very cheap,
> essentially equivalent to a copy.  Going back to from these to
> greyscale is a bit more expensive.
>
> In any case, even 15 milliseconds is longer than we can afford to
> color-convert a frame if the computer is also doing other tasks at the
> same time, so Frank is probably right that we need the frame buffer
> to support different formats in order to eliminate the need for
> conversion.  At the GPU end of things, VTK can handle either
> gray or RGB/RGBA textures right now.
>
> - David
>
>
> Luis Ibanez wrote:
> >
> > Just a quick follow up on our discussion regarding the performance
> > of conversion between color systems.
> >
> > Here is a profile that we got for another project where we are  
> using the
> > FFMPEG library for compressing and decompressing video sequences.
> >
> >
> > In  that particular case we have:
> >
> > 1) Image size 1024 x 768 pixels, greyscale, 1 byte per pixel
> >
> > 2) Computer
> > 2.1)  Dell Precision 450 workstation
> > 2.2) with dual processor Intel Xeon at 2.4GHz
> > 2.3) with 3Gb of RAM
> > 2.4) Linux Debian
> > 2.5) Using the gcc compiler with -O3
> >
> >
> > With this configuration it takes 30 milliseconds to do
> > the following:
> >
> > 0) Copy the input image into another buffer
> > 1) Convert the grayscale image into YUV,
> > 2) Compress the image using the Flash video codec
> > 3) Decompress the image using the Flash video codec
> > 4) Convert the decompressed image back from YUV to grayscale.
> >
> >
> > We have not profiled the conversion in isolation, but the
> > fact that two color format conversions plus video
> > compression and decompression fit in 30 milliseconds,
> > give us some indication on how much the color format
> > conversion alone could take.
> >
> >
> >      Luis
> >
> >
> >
> > ---------------------------------------------------
> > On 3/29/07, *Patrick Cheng* < cheng at isis.georgetown.edu
> > <mailto:cheng at isis.georgetown.edu>> wrote:
> >
> >     Hi everybody,
> >
> >     Here is the minutes for discussion on VideoGrabber continued  
> from
> >     last week:
> >
> >     http://public.kitware.com/IGSTKWIKI/index.php/Minutes_032907
> >
> >     Patrick
> >     _______________________________________________
> >     IGSTK-Developers mailing list
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> >     <mailto: IGSTK-Developers at public.kitware.com>
> >     http://public.kitware.com/cgi-bin/mailman/listinfo/igstk- 
> developers
> >     < http://public.kitware.com/cgi-bin/mailman/listinfo/igstk- 
> developers>
> >
> >
> >  
> ---------------------------------------------------------------------- 
> --
> >
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>
>
> <colorConversionProfiling.cxx>
> <CMakeLists.txt>
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