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I'm doing some image processing to detect bubbles in oil. One of the filters I use creates a grid in my image. OilGrid

If you look closely at the image you can see horizontal and vertical lines through the image forming a grid.

Does anyone know of a way to remove the grid (say by adjusting contrast)without loosing the other image details. I will always know the exact location of the grid.

It would be nice if a program like GIMP could do this.

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Oddly, what I see are tiny "boxes" slightly gradient-ed. Not familiar with Gimp as such, but I guess Gimp would have the Photoshop equivalent of (filter) Despeckle, Dust and scratches, Reduce noise. Try searching for these equivalents. It might be a little extreme sport playing with this, so keep an eye on your oil bubbles. –  Random O'Reilly Jan 6 at 11:50
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The "grid" seems to be a result of broken pixels due to a low resolution image. The best you could do would be to target the areas you do NOT want to retain and blur them. I can't comment on how to do that with GIMP. –  Scott Jan 6 at 13:29
    
If you were wondering, the grid is introduced as a result of a background subtraction algorithm I'm using dsp.stackexchange.com/questions/10329/… –  sav Jan 7 at 2:16

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It appears that you source image is tiled as if a scanner stitched small tiles together. The steps outlined below for Gimp help to reduce these tiles but this will be a lossy process.

Image structure

Small detail of the original image adjusted for black and white levels with "Colors > Levels.." tool reveals the tiling artifact:

enter image description here

Unfortunately the border of each tile has great variance to it's neighbour making it nearly impossible to un-tile the image without a loss of details in the remaining image.

Gaussian Blur

The best results may be obtained with a Gaussian blur, as each tile itself is somewhat blurred as well.

enter image description here

This detail was blurred with Gaussian blur at 14 pixels ("Filters > Blur > Gaussian Blur...").

There still is some tiling to be seen at tiles with a high contrast to it's neigbour. To further reduce this higher values of blur are needed. But these will then further reduce other details of the image.

Contrast Enhancement

We then may again adjust the black and white levels with the "Color > Levels..." tool until the resulting contrast was acceptable.

enter image description here

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