enhance contrast levels, or use full data range
        according to value of self.panel.conf.contrast_level

def set_contrast_levels(self, contrast_level=0):
        """enhance contrast levels, or use full data range
        according to value of self.panel.conf.contrast_level
        """
        for cmap_panel, img_panel in zip((self.cmap_panels[0], self.cmap_panels[1]),
                                         (self.img1_panel, self.img2_panel)):
            conf = img_panel.conf
            img  = img_panel.conf.data
            if contrast_level is None:
                contrast_level = 0
            conf.contrast_level = contrast_level
            clevels = [contrast_level, 100.0-contrast_level]

            jmin = imin = img.min()
            jmax = imax = img.max()
            cmap_panel.imin_val.SetValue('%.4g' % imin)
            cmap_panel.imax_val.SetValue('%.4g' % imax)
            jmin, jmax = np.percentile(img, clevels)

            conf.int_lo[0]  = imin
            conf.int_hi[0]  = imax
            conf.cmap_lo[0] = xlo = (jmin-imin)*conf.cmap_range/(imax-imin)
            conf.cmap_hi[0] = xhi = (jmax-imin)*conf.cmap_range/(imax-imin)

            cmap_panel.cmap_hi.SetValue(xhi)
            cmap_panel.cmap_lo.SetValue(xlo)
            cmap_panel.islider_range.SetLabel('Shown: [ %.4g :  %.4g ]' % (jmin, jmax))
            cmap_panel.redraw_cmap()
            img_panel.redraw()