Encoder apparatus

A readhead for reading an encoder scale having a series of scale markings arranged in a generally periodic pattern that encodes incremental position information, the series of scale markings also including embedded scale features that encode absolute position information,

• the readhead comprising;
• an image sensor comprising a plurality of sensor elements for capturing a snapshot image of a portion of the encoder scale, and
• a position analyser for determining a position of the readhead relative to the encoder scale from the captured snapshot image, the position analyser comprising (i) an absolute position extractor configured to identify the embedded scale features in the snapshot image and to calculate therefrom an absolute position of the readhead relative to the encoder scale, and (ii) an incremental position extractor configured to calculate a global phase value describing an incremental position of the readhead relative to the encoder scale by analysis of the generally periodic pattern of scale markings present in the snapshot image,
• wherein the incremental position extractor is configured to apply an error correction when calculating the global phase value, the applied error correction accounting for variations in the contribution to the calculated global phase value from different sensor elements of the plurality of sensor elements.