To be more complete:
(1) As much as possible, eliminate any uncontrolled ambient lighting, such as daylight throug a window and room lighting (incandescent and fluorescent) that flickers significantly in synchronization with AC power lines. Even physical movement of nearby objects can cause significant changes in reflected light that can result in significant differences in brightness and color of visible surfaces.
(2) Use machine vision lighting that is powered by a filtered DC power source. If there is any flicker from these lights then you may want to make sure that it is not plugged into the same AC circuit as heavy machinery that may create voltage irregularities. Bad DC wiring connections to these lights could also create significant flicker.
(3) Use a narrow band machine vision bandpass filter on your camera lens that matches the wavelength of your LED lighting to significantly reduce the amount of ambient light, relative to your controlled LED lighting.
(4) Set your exposure time to a multiple of 16.67 ms, 1/60th of a second, and use your lens aperture or a LED lighting intensity control to fine-tune the image brightness.
(5) You may also be able to correct for some amount of image brightness variations by including a reference surface of fixed brightness within all of your images and comparing the intensity of other surfaces to your reference brightness.
Running your camera at a frame rate of 30 frames per second will probably not solve this problem because every time that you turn on your vision system you will no longer be synched with the previsous intensity values and the corresponding brightness thresholds.
Good luck!
Nelson Bridwell
http://MachineVision.Engineering
