Title: Flat-field and colour correction for the Raspberry Pi camera module Show Chinese title

Title: 平面场和颜色校正用于树莓派摄像头模块

Abstract: The Raspberry Pi camera module is widely used in open source hardware projects as a low cost camera sensor. However, when the stock lens is removed and replaced with other custom optics the sensor will return a non-uniform background and colour response which hampers the use of this excellent and popular image sensor. This effect is found to be due to the sensor's optical design as well as due to built-in corrections in the GPU firmware, which is optimised for a short focal length lens. In this work we characterise and correct the vignetting and colour crosstalk found in the Raspberry Pi camera module v2, presenting two measures that greatly improve the quality of images using custom optics. First, we use a custom "lens shading table" to correct for vignetting of the image, which can be done in real time in the camera's existing processing pipeline (i.e. the camera's low-latency preview is corrected). The second correction is a colour unmixing matrix, which enables us to reverse the loss in saturation at the edge of the image, though this requires post-processing of the image. With both of these corrections in place, it is possible to obtain uniformly colour-corrected images, at the expense of slightly increased noise at the edges of the image. Show Chinese abstract

Abstract: 树莓派摄像头模块在开源硬件项目中被广泛用作低成本的摄像头传感器。 然而，当原装镜头被移除并替换为其他自定义光学器件时，传感器将返回非均匀的背景和颜色响应，这妨碍了这种优秀且流行的图像传感器的使用。 研究表明，这种现象是由于传感器的光学设计以及GPU固件中的内置校正所致，而该固件是针对短焦距镜头优化的。 在这项工作中，我们对树莓派摄像头模块v2中发现的暗角和颜色串扰进行了表征和校正，并提出了两种能显著提高使用自定义光学器件的图像质量的方法。 首先，我们使用自定义的“镜头阴影表”来校正图像的暗角，这可以在相机现有的处理管道中实时完成（即，相机的低延迟预览被校正）。 第二种校正是一种颜色解混矩阵，它使我们能够逆转图像边缘的饱和度损失，尽管这需要对图像进行后期处理。 有了这两种校正，就可以获得颜色校正均匀的图像，但会略微增加图像边缘的噪声。