Re: [Gnuplot-info] log color bar: out of range data --> invisible

[Ethan M. <eam...@gm...>]

On Fri, Apr 3, 2015 at 3:48 AM, theozh <th...@gm...> wrote:
>> Same way. http://gnuplot.sourceforge.net/docs_4.2/node333.html
>>
>> On Thu, Apr 2, 2015 at 2:19 AM, theozh <th...@gm...
>> <mailto:th...@gm...>> wrote:
>>
>>     That's ok for column data...
>>     But how do you do it with matrix data?
>
> This works if you have your matrix data in column form:
> x1 y1 z1
> x2 y2 z2
> x3 y2 z3
> x4 y4 z4
> ...
>
> But how do you do operation if you have it in matrix form?
> z11 z12 z13 z14
> z21 z22 z23 z24
> z31 z32 z33 z34
> z41 z42 z43 z44

plot $DATA matrix using 1:2:($3<0 ? NaN : $3) with image


> To illustrate the strange observation
>
> If you have a file "Matrix1.dat"
> 1       2       3       4
> 2       -3      4       5
> 3       4       -5      6
> 4       5       6       7
>
> set palette rgbformulae 7,5,15
> set logscale cb
> plot "Matrix1.dat" matrix with image

"set logscale cb" has been buggy/inconsistent for a long time.
Some fixes went into the code recently, but I am not convinced
that it is working consistently even now.   I suggest that if
possible you re-work your plot so that it does not require
log-scaling on the colorbar.

Note that the trick shown above (resetting negative values to NaN)
will cause the corresponding pixels of a "with image" plot to be
omitted altogether - that is, the background color will show
through.  This is unrelated to the min or max values on the
color bar.

FWIW, the following seems to give a correct plot in gnuplot 5
although I think the log scaling is not useful in this case:

~~~~~~
$DATA << EOD
1e-8    2e-8    3e-8    4e-8
2e-8    -3e-8   4e-8    5e-8
3e-8    4e-8    -5e-8   6e-8
4e-8    5e-8    6e-8    7e-8
EOD

set palette rgbformulae 7,5,15
set logscale cb
set cbrange [1e-8:1e-7]

plot $DATA matrix using 1:2:($3<0 ? NaN : $3) with image
~~~~~~

     Ethan






>
> The negative values will be displayed with the minimum color, i.e. black
>
>
> However, if you have a file "Matrix2.dat"
> 1e-8    2e-8    3e-8    4e-8
> 2e-8    -3e-8   4e-8    5e-8
> 3e-8    4e-8    -5e-8   6e-8
> 4e-8    5e-8    6e-8    7e-8
>
> set palette rgbformulae 7,5,15
> set logscale cb
> plot "Matrix1.dat" matrix with image
>
> The negative values will be displayed with the maximum color, i.e. yellow.
>
> What is the reasoning behind that?
>
>
>
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