DIY Laser levelling using webcam and laser level

[devmonkey]

I've now fixed the problem with the dewalt modulation, quite elegantly I think. The modulation was interfering with the rolling shutter on the sensor. All cheap camera sensors employ a rolling shutter, what this means is unlike a real film camera or a DSLR that have global shutters, i.e. the entire frame is exposed simultaneously, a rolling shutter is simply the sensor allows each row to integrate (usually from when it was last read out) and then reads the pixel value for that row after the previous row. This means that each row of the image is exposed at a slightly different time leading to horizontal artifacts such as banding due to 50hz AC lighting, motion blur where an object moving horizontally across the camera may appear to have the bottom leading the top, or vica versa, or in the case of a Dewalt laser level the light source being annoyingly flickered on and off a banding of black lines that moves up the image frame to frame.

Since we are only interested in one dimension (height) the simple fix is to make this dimension perpendicular to the direction of the rolling shutter, i.e turn the sensor through 90 degrees! This has the added advantage given the aspect ratio of the sensor is wider than tall like your TV screen, in giving us more vertical resolution.

Now works like a dream, short video of me deflecting my desk which the sensor is sitting on with light finger pressure, maybe 0.1-0.2mm, watch the PC screen behind reacting. Note you can still see the banding from the modulation but this is now vertically aligned and traveling horizontally so doesn't interfere with our nice gaussian beam.