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MathGroup Archive 2006

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ListDensityPlot and GraphicsArray

  • To: mathgroup at smc.vnet.net
  • Subject: [mg65467] ListDensityPlot and GraphicsArray
  • From: "buttgereit at biomediclab.de" <buttgereit at biomediclab.de>
  • Date: Mon, 3 Apr 2006 06:59:33 -0400 (EDT)
  • Sender: owner-wri-mathgroup at wolfram.com

Dear Group,

using Mathematica 5.0 on WinXP I have a strange problem with
ListDensityPlot.

I have imported a picture (PNG) using

img=Import["mypic.png"];

I can show it, all fine so far.

I then extract the pixel data (rgb in this case) using

raster=img//First//First;

I extract the red channel using

rc=Map[First,raster,{2}];

and can display it with

ListDensityPlot[rc];

However, when I convert the raster to Lab color space and extract, say
the illumination

ListDensityPlot[lc];

fails with

"DensityGraphics::gmat: ... is not a rectangular array larger than 2 x
2"

But the size is identical to rc according to

Dimension[rc] is equal to Dimension[lc] : {400,300}.

Just Reals instead of Integers -- and though, rounding/scaling does not
make a difference.

I have checked the array using

Union[Length/@lc]

which evaluates to {400} in this case -- doesn't this say it _is_
rectangular? Do I miss something?

I can show part of the array using Take and define a region of at most
200x200 pixels -- expanding it again pops the error. I can move that
"window" over the image without errors.
Just expanding it does not work.

Any idea what could cause the problem? ( yes, I did restart windows ;)

Best Regards,

Peter


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