The problem description:
Take a dirty spot on the surface of an object.
If one pixel is used to represent a dirty point, the system will be unstable; therefore, we should take more than three or four pixels to represent a dirty point.
Pixel accuracy = length or width of field of view / length or width of camera resolution
With a field of view of 10mm * 7.5mm and a 1.3 megapixel camera (1280*960), what is the pixel accuracy?
10/1280 = 0.0078mm/pixel
It is required to check the surface scratch of an object. The size of the object is 10mm*8mm, and the inspection accuracy is 0.01mm/pixel. Please choose a camera.
Solution: Assume that one pixel is used to represent a defect, and the field of view of the shot is 12mm*10mm.
The column equation is 0.01=12/x, and the solution is x=1200, which is about 1280*960, 1.3 megapixel camera.
In order to make the system stable to take three pixels to represent a defect, you should choose 130*3, which is the most suitable camera with 3 megapixel.
PS: If you are not using color as a requirement, it is best to choose a black and white camera, because the black and white camera has higher precision at the same resolutio