Photoshop CC new version comes with dehaze feature. You can refer to this post: How to use Dehaze in Photoshop
This is before
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This is after
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If you use old Photoshop or you want to control defog manually, you may have many other options.
- Exposure levels correction. To do that, go to Image>Adjustment>Levels.
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In the histogram, move the left slider in towards the end of the histogram until the object becomes more visible. You can do the same with the right slider.
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2. Unsharp mask. To do that, go to Filter>Sharpen>Unsharp Mask.
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You may try a couple times starting Amount 10% and Radius 20 Pixel; then Amount 20% and Radius 40 Pixel; finally 20% and 80 Pixel.
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3. Contrast. To do that, go to Image>Adjustments>Brightness/Contrast. Adjust the Contrast, for example 60.
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4. Some people say we can try High Pass and Overlay. To do that, go to Filter>Other>High Pass.
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In Layers, change Blending Mode from Normal to Overlay.
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