Pixel binning

Pixel binning refers to the concept of combining the electrical charges of neighboring pixels together to form a superpixel. The main benefit of this technique is that the combined charges would overcome the read noise
at the sacrifice of spatial resolution. Binning in color image sensors results in superpixel Bayer pattern data, and subsequent demosaicking yields the final, lower resolution, less noisy image. It is common knowledge among the practitioners and camera manufacturers,
however, that binning introduces severe artifacts. Our in-depth analysis proves that these artifacts differ from the ones stemming from loss of resolution or demosaicking, and therefore it cannot be eliminated simply by increasing the sensor resolution. We
propose a post-capture binning data processing solution that succeeds in suppressing noise and preserving image details. We verify experimentally that the proposed method outperforms the existing alternatives by a substantial margin.
(http://campus.udayton.edu/~ISSL/index.php/research/binning-artifact-removal/)

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此文末尾有一篇文章的链接《Analysis and processing of pixel binning for color image sensor》（地址），这篇文章是一篇学术论文，感兴趣可以看看！