Fuente: Wipo "digitalization" The present application provides an image sensor and a readout circuit (1) of the image sensor, where the readout circuit (1) of the image sensor is composed of a ramp voltage circuit (10), a comparison circuit (20), a counter circuit (30) and an inversion control circuit (40). When switching a counting, the inversion control circuit (40) is provided to control the counter circuit (30) to invert a first digital code value into a second digital code value, so that in a second quantization time period, the counter circuit (30) is enabled to count based on the second digital code value to generate a third digital code value, thereby a correlated double sampling is realized, a fixed pattern noise is reduced and an imaging quality is improved. Also, in the readout circuit (1), a buffer or an additional holding circuit is no longer in need, thus a circuit structure is simplified, which reduces power consumption, and can ensure that the counter circuit is operated in a high-frequency counting mode.