Obtaining dithered image data word by adding noise contribution

摘要

An image processing method comprises reading out an image sensor array M-bit image data word and adding a noise contribution to the image word to obtain a dithered M-bit word. The noise contribution is derived from correction data having a word size of at least N bits (where N 1) — or M+1 bits - and is derived from combining plural M-bit reference words. Different correction data is derived for different groups of pixels, each associated with a specific pixel value DC shift. The combination of plural M-bit reference words may comprise the average of the reference words, taken from different rows or other pixel array areas, or same pixel rows or areas at different times; reference words may be derived from dark pixel values. Pixel groups may be defined by pixels sharing a common readout block in a column analogue-to-digital converter (ADC) structure, a common readout time, or common detector row. Noise contribution derivation may comprise combining the M most significant bits (MSB) of correction data with a weighted dither contribution derived from the N-M least significant bits (LSB) of correction data. The method is applicable to a mobile telephone, optical mouse or webcam.