[IGSTK-Developers] Tcon minutes March 29, 2007

[David Gobbi]

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
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