Re: [Discuss-gnuradio] File sink file size mismatch problem.

[Tom Rondeau]

On Wed, May 30, 2012 at 3:04 PM, Josh Stevens <address@hidden> wrote:
> Hello All,
>
>       A couple of days ago i had installed a GNURadio digital image
> processing block that makes an image source and sink block available as
> displayed in the image below.
>  Resource : https://github.com/a-w-s/GNURadio-DIP
>  Flowgraph : http://i.imgur.com/1lJzD.png
>
> The output of the image source and the input to the image sink are "floats"
> only and nothing else. I tried to collect pixel information into a file sink
> and i am successful at that but the problem comes in when the size of the
> input file size is not the same as the size of the file sink output.
>
> The image is a basic black and white test image called lena.bmp whose file
> size is 65.0 KB. The link to which is also provided below ,
> Resource to Image :
> https://www.google.com/search?q=lena+256+x+256&hl=en&prmd=imvns&source=lnms&tbm=isch&ei=_G7GT7vkC4rs8wSG99SaBg&sa=X&oi=mode_link&ct=mode&cd=2&sqi=2&ved=0CD8Q_AUoAQ&biw=1280&bih=827
>
> The file size of the received file (file sink) is 76.0 KB.
>
> The reason why I pay more attention to this is because i intend to calculate
> BER / Pixel Error Rate which would take into account a reference stream
> which in this case would be the file with the extra bits , and Image sink
> output ( or the demodulated output) .
>
> Please feel free to ask me any questions that one might have .
>
> Thanks and regards,
> Josh.

Hi Josh,

In general, when doing things like this, there is often some extra
"stuff" that happens because the scheduler works on a per-chunk basis.
So sometimes the size of what's been processed can be confused a bit,
but if you're file is only so large, I wouldn't think this would
happen. Also, 11 KB is a pretty substantial difference in file size.

Do you know where your image is actually located in the output file?
That is, what's the byte offset? (You could try to read this into
Python with scipy or Matlab and do a correlation to see where in the
file the image exists). I'm just trying to help determine if there's
some initial fill or if the extra 11 KB are produced at the end of the
file.

Tom