correct inhomogeneous Illumination

[pa647]

Hi,

i have a problem with inhomogeneous Illumination.

I must illuminate my object from the side, so i have a light gradient from left to right.

Is there any possibility to correct this with a shading matrix or a calculated correction factor from the picture?

Best regards

Andreas Stiller

[muks]

It is not clear to me.Are you trying to acheive uniform lighting?What is the object you are trying to illuminate?

[pa647]

It is a paperboard. I try to make an automatic surface inspection with the photometric stereo.

(I am searching for 3D defects on the surface)

For this i have to illuminate the board from 4 directions (north, south, west and east) and make a picture from the object while holding the viewing geometry constant.

With the image fusion of the north and the south images  and the fusion of west and east i have the possibility to calculate the 3D surface.

But for this it is important that the pictures have nearly the same and a constant brightness.

So after the image correction there should be only slight surface structures visible and not the illumination gradient.

[muks]

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I am searching for 3D defects on the surface

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Did you try low angle lighting techniques using bar leds  

[pa647]

yes,

sure i can still optimize the illumination, but this will not be enough.

i must calculate a calibration factor for each pixel

[muks]

From what i had seen so far. U cannot exactly 100% expect the illumination to be same for each subsequent parts. U need to do histogram equilization and consider lot of other factors like ambient lightings that might affect the image, the lens aperture u r operating at, the consistency of the refction from the part u r inspecting