A method of encoding a mode value representing an intra prediction mode related to a current unit to be encoded using a plurality of most probable mode values, wherein the number of most probable mode values used is three, the method comprising: deriving first and second most probable mode values from respective intra prediction modes of neighbouring units of the current unit, the number of neighbouring units of the current unit being two, and the first and second most probable mode values being different from one another and the deriving comprising: checking whether the respective intra prediction modes of the two neighbouring units of the current unit are the same or different; when the respective intra prediction modes are different, setting the first most probable mode value to a mode value corresponding to one of said respective intra prediction modes, and setting the second most probable mode value to a mode value corresponding to another of said respective intra prediction modes; and deriving a third most probable mode value from the first and second most probable mode values, the third most probable mode value being different from each of said first and second most probable mode values, by, when neither of said first and second most probable mode values corresponds to a planar prediction mode, setting the third most probable mode value to a mode value corresponding to the planar prediction mode; comparing the mode value with at least one of the derived first, second and third most probable mode values; selecting based on the comparison, a first encoding process, from among at least first and second encoding processes, to apply to the mode value to be encoded when the mode value to be encoded is equal to at least one of the first, second and third most probable mode values, and the second encoding process when the mode value to be encoded differs from each of the first, second and third most probable mode values; and encoding the mode value using the selected encoding process, and the first encoding process comprises encoding first information indicating the mode value to be encoded from one of the first, second and third most probable mode values, and the second encoding process comprises encoding second information representing the mode value to be encoded that is not equal to any of the first, second and third most probable mode values and wherein the two neighbouring units comprise the left neighbouring unit and the top neighbouring unit of the current unit. deriving first and second most probable mode values from respective intra prediction modes of neighbouring units of the current unit, the number of neighbouring units of the current unit being two, and the first and second most probable mode values being different from one another and the deriving comprising: checking whether the respective intra prediction modes of the two neighbouring units of the current unit are the same or different; when the respective intra prediction modes are different, setting the first most probable mode value to a mode value corresponding to one of said respective intra prediction modes, and setting the second most probable mode value to a mode value corresponding to another of said respective intra prediction modes; and checking whether the respective intra prediction modes of the two neighbouring units of the current unit are the same or different; when the respective intra prediction modes are different, setting the first most probable mode value to a mode value corresponding to one of said respective intra prediction modes, and setting the second most probable mode value to a mode value corresponding to another of said respective intra prediction modes; and deriving a third most probable mode value from the first and second most probable mode values, the third most probable mode value being different from each of said first and second most probable mode values, by, when neither of said first and second most probable mode values corresponds to a planar prediction mode, setting the third most probable mode value to a mode value corresponding to the planar prediction mode; comparing the mode value with at least one of the derived first, second and third most probable mode values; selecting based on the comparison, a first encoding process, from among at least first and second encoding processes, to apply to the mode value to be encoded when the mode value to be encoded is equal to at least one of the first, second and third most probable mode values, and the second encoding process when the mode value to be encoded differs from each of the first, second and third most probable mode values; and encoding the mode value using the selected encoding process, and the first encoding process comprises encoding first information indicating the mode value to be encoded from one of the first, second and third most probable mode values, and the second encoding process comprises encoding second information representing the mode value to be encoded that is not equal to any of the first, second and third most probable mode values and wherein the two neighbouring units comprise the left neighbouring unit and the top neighbouring unit of the current unit.