defog...what is it?

parhead

I've come across some posts and people claiming to have actions that defog. So, I ask...what exactly is defog? Can some give me a basic definition and maybe a link?

Thanks

DJ-S1

I used to use a version of unsharp mask to "defog", I forget the slider settings now... if you search dgrin I'm sure you can find it. I know I posted it here a few years back.

I use Lightroom now and the Clarify setting seems to do a similar trick.

ChrisKraftPhoto

Ditto on the Unsharp Mask. Using it tends to give your photos more definition.

Amount=between 15-25 although 25 is sometimes a little much
Radius=60
Threshold=0

gluwater

Defogging is basicaly boosting the contrast to make an image more vibrant and less flat. It also sharpens slightly. You may also hear it refered to as adding local contrast. Using unsharp mask, as stated above is an easy way of doing it.

kwcrow

The unsharp mask using the HIRALOAM technique( Acronym for High Radius Low Amount) in the Unsharp Mask Filter. is one way of reducing fog, but in addition to this you can steepen the luminosity curve in the range where the fog is most prominant. Another technique is looking at the individual RGB channel and copy the least foggy or a combination of channels using the channel mixer. (I believe that blue light gets dispersed worse in fog, so it would seem like a combination of the red and green channel together copied into the luminosity channel of LAB mode would be a way to do it another way.
Basically use the channel mixer to create the least foggy black and white image that you can, and copy that BW image into the luminosity channel in Lab mode.


Work flow order
1. Channel mixer get the best fog free black and white image you can from RGB channels. (No blue, combination of red and green, this is why ski goggles and amber vision or blue blocker sunglasses are yellow,to block out foggy blue light).
2. Steepen the curve of this result where the fog is most prominant with the curves tool. Bring end points in to ends of histogram to maximize contrast.
3. Apply HIRALOAM to the image. USM with amount 25-75, Radius 25-75