LinearGradientImage
LinearGradientImage[gcol] returns an image with values linearly changing from left to right based on gradient color gcol.
LinearGradientImage[{pos1,pos2}->gcol] returns an image where the gradient starts at pos1 and ends at pos2.
LinearGradientImage[…,size] returns a linear gradient image of the specified size.
LinearGradientImage[…,size,"type"] gives an image converted to the specified type.
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