Re: cvs: log cb broken

[Petr M. <mi...@ph...>]

> This is new to me, and does not seem to agree with the documentation:
> 
> help autoscale
>     When autoscaling, the axis range is automatically computed and the dependent
>     axis (y for a `plot` and z for `splot`) is scaled to include the range of the
>     function or data being plotted.
> 
> You are saying that for log scales, only the range of the data greater than
> some positive value epsilon is to be scaled?

Yes, it has always worked like that. Hitting "l" for log scale, for any plot 
or splot with at least few positive points, gnuplot produces a reasonable 
drawing.

> I can see how this makes sense for functions, but it strikes me as being
> incorrect for actual data.

Why? Negative values are e.g. electronic noise. The user is not interested 
in, but want to see the image in log scale of intensities.

> Anyhow, I don't quite understand what the equivalent result would be for
> plots "with image".  In the example you give below for log scale on y, only
> points with f(x) > 0 are displayed on the plot.  Would the equivalent for
> "with image" be that individual pixels are only drawn if the value of f(x,y)
> is positive?   That is not what version 4.2 does.
> 
> And what would be the assignment of colors?  Would you limit the colors
> used in the bar to the color range corresponding to positive Z values?
> That would be the logical equivalent of drawing only the positive region
> on y in the example below.  But that is not what 4.2 does.

It should work in 4.3 as 4.2 works: the cb min is 0.1 (the smallest positive 
data point value if "set autoscale fix"), and colors of smaller values are 
drawn same as those corresponding to this minimum.

It works everywhere like this for the cb axis. Try for example this:

	splot x*x-y*y*2 with pm3d
	set log cb
	replot

and the colors below the limit are black.
If you want to mask out some rectangles, then you need
	set log z; replot

Consequently, there is a bug in 4.3. 
Wasn't it introduced in your patch from 2007-12-18?
 
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PM