Abstract: Electronic devices may be provided with image sensors. Image sensors may be configured to capture images during imaging operations and monitor ambient light levels during non-imaging operations. An image sensor may include image pixels that receive light and dark pixels that are prevented from receiving light. An image sensor may include an ambient light detection circuit. The ambient light detection circuit may include an oscillator, timing and control circuitry, and a counter. The oscillator may be switchably coupled to the image pixels and the dark pixels. The counter may be configured to count up oscillator cycles of the oscillator while the oscillator is coupled to the image pixels and to count down oscillator cycles of the oscillator while the oscillator is coupled to the dark pixels. The counter may provide a count value that depends on a signal from the image pixels and a signal from the dark pixels.

Abstract: Imaging systems may be provided with image sensors and verification circuitry. Verification circuitry may be configured to continuously verify proper operation of the image sensor during operation. Verification circuitry may include one or more heating elements formed on a common substrate with image pixels of the image sensor. Verification data may be generated by powering on the heating elements and collecting charges generated in image pixels of the image sensor in response to heat generated by the powered heating element. Heat image charges may be read out using the same readout circuitry that is used to readout imaging data generated in response to incoming light. Heat image data may be used to verify proper operation of all components of an imaging system. Based on a comparison of the verification data with a predetermined standard, an imaging system may continue to operate normally or corrective action may be taken.

Abstract: A method for preprocessing analog image data to reduce noise in the analog image data that is readout from a pixel array of an image sensor during a sampling time is disclosed. The method includes generating multiple samples of the analog image data during the sampling time and then limiting values of the multiple samples to an upper and lower threshold. The method also includes pre-conditioning the multiple samples by applying a weighting factor to each of the multiple samples in response to when a respective sample was generated during the sampling time. A median value of the multiple samples is then determined and outputted.

Abstract: Imaging systems may be provided with image sensors having verification circuitry. Verification circuitry may be configured to verify proper operation of the image sensor during operation. Verification circuitry may include one or more switchable voltage contacts configured to generate a voltage drop across a power supply network of a pixel array during verification operations. Verification circuitry may include a controllable voltage supply coupled to the power supply network of the pixel array. Verification image data may be generated by applying the voltage drop or by using the controllable voltage supply to supply a different supply voltage to each row of pixels prior to readout of that row. Verification image data may be read out using the same circuitry that is used to readout imaging data. Based on a comparison of the verification data with a predetermined standard, imaging systems may continue to operate normally or corrective action may be taken.

Abstract: Electronic devices may be provided with image sensors. Image sensors may be configured to capture images during imaging operations and monitor ambient light levels during non-imaging operations. An image sensor may include image pixels that receive light and dark pixels that are prevented from receiving light. An image sensor may include an ambient light detection circuit. The ambient light detection circuit may include an oscillator, timing and control circuitry, and a counter. The oscillator may be switchably coupled to the image pixels and the dark pixels. The counter may be configured to count up oscillator cycles of the oscillator while the oscillator is coupled to the image pixels and to count down oscillator cycles of the oscillator while the oscillator is coupled to the dark pixels. The counter may provide a count value that depends on a signal from the image pixels and a signal from the dark pixels.

Abstract: Imaging systems may be provided with stacked-chip image sensors. A stacked-chip image sensor may include a vertical chip stack that includes an array of image pixels, control circuitry and storage and processing circuitry. The image pixel array may be coupled to the control circuitry using vertical metal interconnects. The control circuitry may provide digital image data to the storage and processing circuitry over additional vertical conductive. The stacked-chip image sensor may be configured to capture image frames at a capture frame rate and to output processed image frames at an output frame rate that is lower that the capture frame rate. The storage and processing circuitry may be configured to process image frames concurrently with image capture operations. Processing image frames concurrently with image capture operations may include adjusting the positions of moving objects and by adjusting the pixel brightness values of regions of image frames that have changing brightness.

Abstract: An imager including a self test mode. The imager includes a pixel array for providing multiple pixel output signals via multiple columns; and a test switch for (a) receiving a test signal from a test generator and (b) disconnecting a pixel output signal from a column of the pixel array. The test switch provides the test signal to the column of the pixel array. The test signal includes a test voltage that replaces the pixel output signal. The test signal is digitized by an analog-to digital converter (ADC) and provided to a processor. The processor compares the digitized test signal to an expected pixel output signal. The processor also interpolates the output signal from a corresponding pixel using adjacent pixels, when the test switch disconnects the pixel output signal from the column of the pixel array.

Abstract: Imaging systems may be provided with stacked-chip image sensors. A stacked-chip image sensor may include a vertical chip stack that includes an array of image pixels, analog control circuitry and storage and processing circuitry. The array of image pixels, the analog control circuitry, and the storage and processing circuitry may be formed on separate, stacked semiconductor substrates or may be formed in a vertical stack on a common semiconductor substrate. The image pixel array may be coupled to the control circuitry using vertical metal interconnects. The control circuitry may route pixel control signals and readout image data signals over the vertical metal interconnects. The control circuitry may provide digital image data to the storage and processing circuitry over additional vertical conductive interconnects coupled between the control circuitry and the storage and processing circuitry. The storage and processing circuitry may be configured to store and/or process the digital image data.

Abstract: An imaging system may include an array of image pixels. The array of image pixels may be provided with one or more rows and columns of optically shielded dark image pixels. The dark image pixels may be used to produce verification image data that follows the same pixel-to-output data path of light-receiving pixels. The output signals from dark pixels may be continuously or intermittently compared with a set of expected output signals to verify that the imaging system is functioning properly. In some arrangements, verification image data may include a current frame number that is encoded into the dark pixels. The encoded current frame number may be compared with an expected current frame number. In other arrangements, dark pixels may be configured to have a predetermined pattern of conversion gain levels. The output signals may be compared with a “golden” image or other predetermined set of expected output signals.

Abstract: Imaging systems may be provided with image sensors and verification circuitry. Verification circuitry may be configured to continuously verify proper operation of the image sensor during operation. Verification circuitry may include one or more heating elements formed on a common substrate with image pixels of the image sensor. Verification data may be generated by powering on the heating elements and collecting charges generated in image pixels of the image sensor in response to heat generated by the powered heating element. Heat image charges may be read out using the same readout circuitry that is used to readout imaging data generated in response to incoming light. Heat image data may be used to verify proper operation of all components of an imaging system. Based on a comparison of the verification data with a predetermined standard, an imaging system may continue to operate normally or corrective action may be taken.

Abstract: Imaging systems may be provided with image sensors having verification circuitry. Verification circuitry may be configured to verify proper operation of the image sensor during operation. Verification circuitry may include one or more switchable voltage contacts configured to generate a voltage drop across a power supply network of a pixel array during verification operations. Verification circuitry may include a controllable voltage supply coupled to the power supply network of the pixel array. Verification image data may be generated by applying the voltage drop or by using the controllable voltage supply to supply a different supply voltage to each row of pixels prior to readout of that row. Verification image data may be read out using the same circuitry that is used to readout imaging data. Based on a comparison of the verification data with a predetermined standard, imaging systems may continue to operate normally or corrective action may be taken.

Abstract: Imaging systems may be provided with image sensors having verification circuitry. Verification circuitry may be configured to continuously or occasionally verify that the image sensor is functioning properly. For example, verification circuitry may be configured to monitor levels of leakage current during standby mode. Verification circuitry may be coupled between a power supply and circuitry that is powered by that power supply. When the imaging system is in standby mode, circuitry associated with the imaging system such as pixel circuitry may draw a standby leakage current. Verification circuitry may be configured to measure the amount of standby leakage current drawn by associated imaging system circuitry. If the measured level of standby leakage current exceeds a maximum acceptable level of standby leakage current, a warning signal may be generated. Standby leakage current levels on multiple power supply lines may be monitored with associated verification circuitry.

Abstract: Multiple-exposure high dynamic range image processing may be performed that filters pixel values that are distorted by blooming from nearby saturated pixels. Pixel values that are near saturated pixels may be identified as pixels that may be affected by blooming. The contributions from those pixels may be minimized when producing a final image. Multiple-exposure images may be linearly combined to produce a final high dynamic range image. Pixel values that may be distorted by blooming may be given less weight in the linear combination.

Abstract: An image sensor may include an image pixel array. The image sensor may be provided with automatic conversion gain selection on a pixel-by-pixel basis to produce a high-dynamic-range image. Each image pixel may include a capacitor and a conversion gain transistor coupled in series between a power supply line and a floating diffusion node. The conversion gain transistor may be coupled to a control line through a gating transistor. The gating transistor may have a gate connected to a row select line. The image pixel may have an output line that is coupled to a column amplifier and a comparator. The column amplifier may generate a difference voltage based on reset and image signals. The comparator may compare the difference voltage with a predetermined threshold to determine whether to place the selected pixel in a high or low conversion gain mode.

Abstract: High-dynamic-range images may be produced by combining multiple integration periods of varying duration, wherein each integration is obtained using a global shutter operation. Charge accumulated during a first integration period may be stored on a first storage node while charge accumulated during a second and third integration time are carried out. Storage of charges accumulated during the second and third integration periods on a second storage node within a pixel while charge is stored on the first storage node allows capture of a global-shutter-based, high-dynamic-range image. A global-shutter-based image capture base on at least three integration time periods may provide enhanced dynamic range.

Abstract: Imagers reproduce an image by converting photons to a signal that is representative of the image. A sensor readout module reads reset and signal voltages corresponding to a plurality of integration times for each of a plurality of pixels. The sensor readout module is capable of determining whether the differences between reset and signal voltages corresponding to respective integration times indicate a saturation condition of the pixel. Accordingly, the sensor readout module may provide an output signal based on reset and signal voltages corresponding to an integration time that is less than an integration time for reset and signal voltages that indicate the saturation condition. A normalization module may normalize the output signal to correspond with a linear response curve.

Abstract: A method, apparatus and system are described providing a high dynamic range pixel. Operating conditions, including integration time and sensitivity of different photosensors, and signal processing, including gain settings, are selected to provide multiple possible response curves. An output is selected from the possible response curves and used to provide an overall pixel response curve to increase the pixel dynamic range.

Abstract: An imaging method and apparatus which use a pixel array for capturing images and for measuring ambient light conditions.

Abstract: Imagers reproduce an image by converting photons to a signal that is representative of the image. A sensor readout module reads reset and signal voltages corresponding to a plurality of integration times for each of a plurality of pixels. The sensor readout module is capable of determining whether the differences between reset and signal voltages corresponding to respective integration times indicate a saturation condition of the pixel. Accordingly, the sensor readout module may provide an output signal based on reset and signal voltages corresponding to an integration time that is less than an integration time for reset and signal voltages that indicate the saturation condition. A normalization module may normalize the output signal to correspond with a linear response curve.

Abstract: Methods, systems and apparatuses for using regular and/or dark pixels of a pixel array in either a fixed or dynamic fashion to compensate for fixed pattern noise.