computer-vision - 为什么相机内在矩阵中的焦距有两个维度？

Question

在 pinhole camera model主点和相机中心之间只有一个焦距。

然而，在计算相机的内在参数后，矩阵包含

(fx,  0,  offsetx,  0,
 0,  fy,  offsety,  0,
 0,   0,  1,        0)

这是因为图像传感器的像素在 x 和 y 上不是方形的吗？

谢谢你。

Answer 1

简而言之:是的。为了建立一个可以用矩形像素描述相机的数学模型，你必须引入两个独立的焦距。我将引用经常推荐的“Learning OpenCV”(第 373 页)，它很好地涵盖了该部分，如果您想了解更多背景信息，我建议您阅读:

The focal length fx (for example) is actually the product of the physical focal length of the lens and the size sx of the individual imager elements (this should make sense because sx has units of pixels per millimeter while F has units of millimeters, which means that fx is in the required units of pixels). [...] It is important to keep in mind, though, that sx and sy cannot be measured directly via any camera calibration process, and neither is the physical focal length F directly measurable. Only the combinations fx = F*sx and fy = F*sy can be derived without actually dismantling the camera and measuring its components directly.