colorm.go
func (c *ColorM) SetElement(i, j int, element float64) {
	c.impl = c.impl.SetElement(i, j, float32(element))
}
func (c *ColorM) SetElement(i, j int, element float64) {
	c.impl = c.impl.SetElement(i, j, float32(element))
}
// SetElement sets an element at (i, j).