Re: imagesc.m scaling

For anyone interested, attached is a zip file of gnuplot image related code.  Put the files in a path and create links, i.e.,

ln -s image_gp.m image.m
ln -s imagesc_gp.m imagesc.m
ln -s imshow_gp.m imshow.m

The imagesc.m function properly creates a colorbox matching the data values.

Dan


Daniel J Sebald wrote:
> I haven't been following the graphics set up for octave real closely.  
> (It would be nice to have a summary or review of how things are being 
> set up and progressing.  Last I heard is that graphics was going to be 
> put into separate modules or m-scripts associated with the plotting 
> method used.  E.g., there would be a group of m-scripts for "plot", 
> "image", etc. for gnuplot.)  Anyway, I'm looking at the imagesc.m script 
> for 2.1.65 and I question if physically scaling the data and then using 
> "image.m" is correct.
> 
> That is, this piece of code inside imagesc.m:
> 
>  ## scale the limits to the range of the colormap
>  if (maxval == minval)
>    B = ones (size (A));
>  else
>    ## Rescale values to between 1 and length (colormap) inclusive.
>    B = round ((A - minval) / (maxval - minval) * (rows (colormap) - 1)) 
> + 1;
>  endif
> 
> The problem with the above is that when used in gnuplot and the colorbox 
> is active, the range on the colorbox makes no sense with regard to the 
> original data.  (Some may argue that color boxes aren't supported... but 
> I'd like one.)
> 
> What I see as the only difference between image.m and imagesc.m is that 
> the "cbrange" (gnuplot's term) is different.  In the case of image.m, it 
> is from 0 to N-1 where N is the size of the palette.  In the case of 
> imagesc.m, it is from the min of the data to the max of the data (or 
> [Hi:Lo] if specified).
> 
> Since Octave's gnuplot image support isn't far enough along yet, the 
> following would be for my own setup.  But I'd propose the following layout
> 
> __image__.m:  Similar to the modified-for-gnuplot-with-image image.m I 
> created as it currently stands.
> 
> image.m:  Set cbrange to 0 to N-1, call __image__.m
> 
> imagesc.m:  Set cbrange to min:max or HI:LO, call __image__.m
> 
> Any thoughts for those who might be working on gnuplot support?
> 
> Dan
> 


-- 

Dan Sebald
phone: 608 256 7718
email: daniel DOT sebald AT ieee DOT org
URL: http://acer-access DOT com/~dsebald AT acer-access DOT com/