Saturday, October 04, 2014

Omnivision Proposes Increasing Pixel Crosstalk in RGBC Sensors

Omnivision patent application US20140267848 "Image sensor with pixels having increased optical crosstalk" by the company's President Raymond Wu says "some RGBC patterns may suffer from color aliasing. [...] Color aliasing occurs at least partly due to the alignment of the clear filters within the RGBC pattern. Image sensors with clear pixels are more prone to color aliasing since clear pixels do not produce any color information of their own other than the intensity of light."

"Accordingly, embodiments of the present disclosure intentionally increase optical crosstalk in the pixel array in order to reduce the effect of color aliasing. [...] In conventional image sensors, optical crosstalk is an unfavorable effect that is mitigated because light straying from neighboring pixels may tend to distort the true color information of the target pixel. However, optical crosstalk has the unexpected benefit of blending the color of the target pixel with its neighboring pixels, thereby reducing color aliasing. Embodiments of the present disclosure intentionally induce and/or increase optical crosstalk as a desirable feature of CMOS image sensors to reduce the effects of color aliasing. may be advantageous to have color pixels increase crosstalk, but to have clear pixels not. In other words, light incident on color pixels may be directed into neighboring clear pixels, but light incident on clear pixels will substantially remain within the clear pixels.

Few ways to increase the crosstalk are proposed. The one below shows a BSI example:


  1. You can simulate increased crosstalk in the ISP by taking a linear combination of neighboring pixels. This is akin to filtering. Similarly, you can simulate reduced crosstalk by inverse filtering/deconvolution.

    Crosstalk has no effect on aliasing. It does have a pronounced effect on noise.

    1. Crosstalk in ISP does not solve aliasing problems. One needs optical LPF or other similar means to limit the high spatial frequencies.

    2. B and G lights suggest to absorb in B and G pixel "completely" because of lesser absorption depth. But R pixel exchanges with C pixel stronger and R portion of light from R goes to C and from C to R reciprocally. This could only mean that "...light incident on clear pixels will substantially remain within the clear pixels." At that all color pixels experience the increased optical crosstalk.


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