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MathGroup Archive 2007

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Re: Joint Histogram

  • To: mathgroup at smc.vnet.net
  • Subject: [mg81153] Re: Joint Histogram
  • From: "Mariusz Jankowski" <mjankowski at usm.maine.edu>
  • Date: Fri, 14 Sep 2007 03:34:25 -0400 (EDT)
  • Organization: University of Southern Maine
  • References: <fcb3gv$fg5$1@smc.vnet.net>

The first answer is to use function JointImageHistogram in the Digital Image
Processing package.

However, the following will work:


In[1]:= beans =
Import["http://www.ee.usm.maine.edu/courses/ele489/data/beans.tif";]

In[2]:= data = beans[[1, 1]];

In[3]:= {ydim, xdim} = Dimensions[data];

In[4]:= h = Table[0, {256}, {256}];

In[5]:= Do[ h[[data[[i, j, 1]] + 1, data[[i, j, 2]] + 1]] += 1, {i, ydim},
{j, xdim}]


... and display matrix h.


Bye, Mariusz







>>> On 9/13/2007 at 6:30 AM, in message <fcb3gv$fg5$1 at smc.vnet.net>,
cimon<tamanna.arora at gmail.com> wrote:
> Hello
> 
> I am completely new to Mathematica
> and trying to work with images in it.
> 
> I am trying to create a joint histogram out of an image taking its red
> and green channel.
> I get this error
> 
> Table::iterb: Iterator (i,1,ydim),  does not have appropriate bounds.
> Table::iterb: Iterator (i,1,ydim),  does not have appropriate bounds.
> 
> (see in code below)
> 
> When I have just written the first five lines and i try to execute. i
> dont get this error.
> But when I have written the for loop and than i try to execute than I
> get this error.
> 
> 
> I am just not able to fix this out.
> can somebody plese guide me with this.
> -------------------------------------------------------------------------
> penny = Import["c:\penny.ppm"];
> Shallow[penny];
> data = penny[[1, 1]];
> 
> ydim = Dimensions[data][[1]];
> xdim = Dimensions[data][[2]];
> 
> Table::iterb: Iterator (i,1,ydim),  does not have appropriate bounds.
> Table::iterb: Iterator (i,1,ydim),  does not have appropriate bounds.
> 
> (* Create a Joint table
>     Go to each (i, j)th Location in red and green Channel
>     Get Pixel value from (i, j)th location from each red and green
> channel
>     Use that as an index into
>     Joint Table and incerment the value at that index by 1
>   *)
> 
> Joint = Table[0, {ti, 1, 256}, {tb, 1, 256}];
> Dimensions[Joint];
> 
> 
> For[fi = 0, fi =E2=89=A4 xdim, fi++
>       For[fj = 0, fj =E2=89=A4 ydim, fj++
>             Joint[redChannel[[fi, fj]], greenChannel[[fi, fj]]] +=
> 1]];
> 
> Show[Graphics[Raster[Joint], AspectRatio -> 1, Axes -> True]]
> 
> 
>
---------------------------------------------------------------------------=

> ------------------------------------


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