Is this formula correct??

1 次查看（过去 30 天）

Carole 2012-12-3

0
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/55569-is-this-formula-correct

Hello,

To find the real size of an object can I use this formula

Objects original size (in m) = Objects size on sensor (in mm) * distance between camera and object (in m) / focal length (in mm)

knowing these informations

size of object: 400 pixels

working distance: 31 mm

http://s8.postimage.org/eea3ekm5x/d_tails1.jpg

http://s17.postimage.org/9zhwkxv67/d_tail2.jpg

thanks

4 个评论
显示 2更早的评论隐藏 2更早的评论

Walter Roberson 2012-12-3

We still don't understand why you don't just put an object of known size into the device and measure on the resulting image??

Carole 2012-12-3

I can't do this because I don't have the device used. I have just the image.

请先登录，再进行评论。

请先登录，再回答此问题。

回答（1 个）

Image Analyst 2012-12-3

2
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/55569-is-this-formula-correct#answer_67370

Yes, that is the thin lens equation. Do you have all those quantities? Note that the size of the object is in mm, not pixels. So you have to know what length 400 pixels corresponds to on your sensor. And 31 mm is awfully close - are you sure the thin lens equation holds in that kind of "macro focus" situation? I have doubts. And if you use a good lens, for things very close (not at infinity) then the thin lens equation is not so clear. The working distance (scene-to-front of lens) is not the same as the scene-to-front principal plane for a thick lens.

This seems like the hard way of doing it though. Why not just measure something of a known length to get a spatial calibration factor?