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Description
Bug report
Bug summary
When using a decreasing Norm, colorbars show no ticks.
Code for reproduction
This example uses a PowerNorm-like norm which first applies the power, then does linear rescaling to (0, 1) (as opposed to matplotlib's PowerNorm which first linearly rescales to (0, 1) then applies the power) -- as argued in#10234 the behavior here is often more desirable, though that's not the point of this bug report.
PNorms with a negative gamma are decreasing (the builtin PowerNorm wouldn't work here because the first linear rescaling step would put the minimum to zero, which doesn't like being raised to a negative power...).
frommatplotlibimportpyplotaspltfrommatplotlib.colorsimportNormalizeimportnumpyasnpclassPNorm(Normalize):def__init__(self,vmin=None,vmax=None,clip=False,*,gamma):super().__init__(vmin=vmin,vmax=vmax,clip=clip)self.gamma=gammadef__call__(self,value,clip=None):ifclipisNone:clip=self.clipresult,is_scalar=self.process_value(value)self.autoscale_None(result)vmin,vmax=self.vmin,self.vmaxgamma=self.gammaifvmin>vmax:raiseValueError("minvalue must be less than or equal to maxvalue")elifvmin==vmax:result.fill(0)else:ifclip:mask=np.ma.getmask(result)result=np.ma.array(np.clip(result.filled(vmax),vmin,vmax),mask=mask)resdat=result.dataresdat=resdat**gammaresdat-=min(vmin**gamma,vmax**gamma)resdat/=abs(vmax**gamma-vmin**gamma)result=np.ma.array(resdat,mask=result.mask,copy=False)ifis_scalar:result=result[0]returnresultdefinverse(self,value):ifnotself.scaled():raiseValueError("Not invertible until scaled")ifnp.iterable(value):returnnp.vectorize(self.inverse)(value)else:vmin,vmax=self.vmin,self.vmaxgamma=self.gammareturn (value*abs(vmax**gamma-vmin**gamma)+min(vmin**gamma,vmax**gamma))** (1/gamma)fig,axs=plt.subplots(1,2)im=axs[0].imshow(np.arange(1.,101.).reshape((10,10)),norm=PNorm(gamma=2))fig.colorbar(im,ax=axs[0])im=axs[1].imshow(np.arange(1.,101.).reshape((10,10)),norm=PNorm(gamma=-2))fig.colorbar(im,ax=axs[1])plt.show()
(as a side note, creating new norms is a bit ridiculously verbose)
Actual outcome
left is gamma=2, right is gamma=-2.
Expected outcome
Some ticks on the right (gamma=-2) colorbar.
Matplotlib version
- Operating system: Arch Linux
- Matplotlib version: 3.0.1
- Matplotlib backend (
print(matplotlib.get_backend())): any - Python version: 3.7