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Given a colour image whose light intensity is dim at the edges and bright in the middle, such as [dim bright dim], which computer vision technique would be recommended to correct this imbalance?

While I believe Histogram Equalisation could help, I've read that it also introduces an unrealistic look to an image by exaggerating the blue channel.

I consider implementing an image processor for this task.

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One classic approach is using top hat filtering for leveling uneven illumination. You should perform morphological opening with a large structuring element, then remove the result from the original image.

If you have dark objects on light background you should do bottom hat filtering (dual of top hat filtering): subtract the closing with a large structuring element from the original image.

Result of top hat filtering

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  • Thanks WebMonster. I'll take a look at this as I've never heard the name before. Does this approach work equally as well with coloured images as it does greyscale?
    – BlackBox
    Commented Apr 30, 2014 at 19:30
  • I don't know if there is a generalization of morphological operators for colored images. You could convert the image to HSV color space, process the V channel as a grayscale image, then display the image. There will be some colour bleeding, but it could be good enough depending on your goals.
    – WebMonster
    Commented Apr 30, 2014 at 20:37

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