A method of constructing, in a decoder, a lookup table for prediction of high dynamic range image data from standard dynamic image data, the method comprising: accessing a prediction function for the prediction of high dynamic range image data from standard dynamic image data; generating a first set of nodes for a first lookup table, using the prediction function, wherein each node is characterized by an input node value and an output node value; modifying the output node value of at least one node in the first set of nodes to generate a second set of nodes in a second lookup table, for generating predicted high dynamic range output values, said modifying comprising: for a current node ( N cb ( i)) in the first set of nodes: determining a first prior node ( N cb ( i -1)) and a second prior node ( N cb ( i -2)) to the current node, wherein the first prior node is closer to the current node than the second prior node; determining a first slope ( S p 1 ( i)) between the first prior node and the current node; determining a second slope ( S p 2 ( i) between the second prior node and the first prior node; determining a first tangent slope ( T(i -1)) to the first prior node based on the first slope and the second slope; determining a first modified slope ( S p ( i)) based on the first tangent slope, the first slope, and a weighting parameter; and determining a first modified output value N cb p i of the current node based on the first modified slope and the first prior node. accessing a prediction function for the prediction of high dynamic range image data from standard dynamic image data; generating a first set of nodes for a first lookup table, using the prediction function, wherein each node is characterized by an input node value and an output node value; modifying the output node value of at least one node in the first set of nodes to generate a second set of nodes in a second lookup table, for generating predicted high dynamic range output values, said modifying comprising: for a current node ( N cb ( i)) in the first set of nodes: determining a first prior node ( N cb ( i -1)) and a second prior node ( N cb ( i -2)) to the current node, wherein the first prior node is closer to the current node than the second prior node; determining a first slope ( S p 1 ( i)) between the first prior node and the current node; determining a second slope ( S p 2 ( i) between the second prior node and the first prior node; determining a first tangent slope ( T(i -1)) to the first prior node based on the first slope and the second slope; determining a first modified slope ( S p ( i)) based on the first tangent slope, the first slope, and a weighting parameter; and determining a first modified output value N cb p i of the current node based on the first modified slope and the first prior node. determining a first prior node ( N cb ( i -1)) and a second prior node ( N cb ( i -2)) to the current node, wherein the first prior node is closer to the current node than the second prior node; determining a first slope ( S p 1 ( i)) between the first prior node and the current node; determining a second slope ( S p 2 ( i) between the second prior node and the first prior node; determining a first tangent slope ( T(i -1)) to the first prior node based on the first slope and the second slope; determining a first modified slope ( S p ( i)) based on the first tangent slope, the first slope, and a weighting parameter; and determining a first modified output value N cb p i of the current node based on the first modified slope and the first prior node.