Methods and apparatus, including computer program products, for filtering an image. A filter kernel is received to determine one or more filtered values for each pixel in a sequence of pixels, where adjacent pixels are separated by a characteristic distance in the image. A difference kernel is defined based on local differences between a first kernel and a second kernel that are defined by the filter kernel centered at a first location and a second location, respectively. The second location is separated from the first location by the characteristic distance separating adjacent pixels in the sequence. The difference kernel is used to determine a difference between filtered values of adjacent pixels in the sequence. For depth of field filtering, the filter kernel can include a blur filter kernel that is based upon depth values of pixels in the sequence.

Methods and apparatus, including computer program products, for filtering an image including a plurality of pixels. A forward kernel centered at a first pixel in the image is received. The forward kernel assigns forward weights to pixels in a neighborhood surrounding the first pixel. A backward kernel centered at a second pixel within the neighborhood surrounding the first pixel is specified based on a local attribute of the image at the second pixel. The backward kernel assigns backward weights to pixels in a neighborhood surrounding the second pixel. A convolution weight of the second pixel is determined based on the backward kernel and the forward kernel. The convolution weight and a pixel value of the second pixel are used to generate a new value of the first pixel.

An image sensor includes a sensor or a pixel array, a data memory, and a logic circuit, all fabricated on the same integrated chip. The sensor or pixel array outputs digital signals as pixel data representing an image of a scene. The data memory is coupled to the sensor or pixel array for storing the pixel data. The logic circuit is coupled to the data memory and provides a memory interface for exporting the pixel data. The memory interface can be one of a SRAM, a DRAM or a packet protocol synchronous DRAM interface. Including a memory interface in the image sensor allows the image sensor to be coupled directly to the memory interface port of an external image processing unit. The image processing unit can access the image sensor using conventional memory access protocols, thus improving the efficiency and reducing the operational complexity of the image processing unit.