# EEVblog Electronics Community Forum

## Electronics => Metrology => Topic started by: chakradhar on January 13, 2016, 05:25:15 am

Title: Weighted Averages For Analogue Signal
Post by: chakradhar on January 13, 2016, 05:25:15 am
Weighted averages for knowing the brightest spot on a ccd sensor.
Title: Re: What Algorithms For CCD based shaft Alignment Laser device
Post by: rs20 on January 13, 2016, 05:45:01 am
You can (at least in theory) find the position of a star in a photograph of the sky to an accuracy of less that one pixel. It's straightforward to do:

-- If there's one bright pixel, then the star is centered in that pixel.
-- If there's two bright pixels of equal brightness, then the star is halfway inbetween.
-- If there's two bright pixels, but one is slightly brighter, then obviously it's closer to that pixel.

In practice, you just find the "centre of light" (by analogy to the centre of mass) of the image. A weighted average of the coordinates of the pixels in the image, weighted by the brightness of each pixel.

Presumably your device is doing a similar thing, except  it's even simpler because it's only 1 dimensional.
Title: Re: What Algorithms For CCD based shaft Alignment Laser device
Post by: LaserSteve on January 15, 2016, 02:55:46 pm
POSSIBLY Diffraction patterns from the edges of the target and interpolation. ALSO can use the intensity distribution of the laser. If the laser was on a piezo, even better.

Steve
Title: Re: What Algorithms For CCD based shaft Alignment Laser device
Post by: mjs on January 22, 2016, 03:13:16 pm
The laser beam probably has about gaussian intensity profile, which hits multiple pixels. Calculating the centroid of the beam can easily give sub-pixel accuracies. You may need to take into account the thermal expansion of the silicon chip, as 50K temperature change expands the chip lenght by about 3um  :)

From a good quality 2D astronomical image millipixel resolution is easy and there are articles about micropixel resolutions!
Title: Re: What Algorithms For CCD based shaft Alignment Laser device
Post by: chakradhar on January 25, 2016, 11:22:00 am
Thanks a lot for the replies. This will get me started ...  working on the possible algorithms based on the ideas.