QGIS » QGIS Application

It is possible to invert the gradient in rasters (before classifying), but not in vectors. It should be easy to add a "invert" checkbox next to the color ramp selector in the Categorized and Graduated modes.

Updating the various gradient dialogs to support inverted colors would be somewhat more involved.

IMHO inverting palette is not feasible with cpt-city gradients.

Actually, implementing "invert palette" shouldn't be too hard.

The question is, where should this option appear? In the gradient dialog boxes, or in the raster/vector classification UIs (as is done for "invert colors")?

Another question is: is this really necessary?

Here is the relevant code in the 1-band raster colour table plugin (bcccoltbl), in file Palette.py, that does the inversions.

    # interfaces to export useful objects
    def getColPalette(self, bInvert = False, bReverse = False):
        """ 
        -- return the colour palette array
        """ 
        if bInvert:
            #invert the colour palette
            for i in range(self.nColo+1):
                self.arColo[i,0] = 255 - self.arColo[i,0]
                self.arColo[i,1] = 255 - self.arColo[i,1]
                self.arColo[i,2] = 255 - self.arColo[i,2]
        if bReverse:
            #reverse the colours order
            ar = np.zeros((self.nColo+1,4),int)
            n = self.nColo
            for i in range(self.nColo+1):
                ar[i,0] = self.arColo[n -i,0]
                ar[i,1] = self.arColo[n -i,1]
                ar[i,2] = self.arColo[n -i,2]
            self.arColo = ar
        return self.arColo

Added a few people to this ticket, would appreciate feddback on questions raised in last comment.

Not sure it is necessary. I'd put it besides the "invert colour" checkbox.