Undoing excessive polarizer effect

[harvey]

I was interested in the article "Faking a polarizer using RAW" on photoclubalpha.com but I have the opposite problem. How do I balance out a sky that is too uneven due to a part of it being more affected by use of a polarizer?

Here is an example image to show the problem:



I have Photoshop CS2 and the closest I can get is by using the replace color image adjustment but it is not very good. I'm wondering if I need a filter that would lighten/darken or saturate/desaturate towards a chosen reference.

Any suggestions on the best way to do this?

Harvey

[Hawk]

I'm not post processing expert, but depending how many blue objects are on photo I'd play with blue and cyan saturation, luminance, lightness and levels. First two you may access via Hue/Saturation in Adjustements menu. Other two via Levels option in same menu. I may give it a try on test photo that you posted here, however I don't have any image editor available at the moment.

If that changes will render photo unnatural additional processing may be required of course.

[David Kilpatrick]

On that shot, your safest bet is to replace the entire sky with a decent sky shot normally on another day. You could try changing blue luminance, but there's too much neutral density in the dark sky for this to work fully.

Go out and shoot a similar angle of sky, at the same ISO, in a place with a low horizon such as over water, to give you a large sky to work with to drop in.

David

[Hawk]

I'm not sure if thats what you wanted, but I've edited your sample photo to gave the sky different look. Some clouds were lost however. Magic wand was used to select sky (I was too lazy to do exact selection, so some pixels may be unchanged ruining an effect, sorry but its late here ). Following changes were made on selection: midtone levels set to 2.95, output levels were shifted by 60 from black towards white, +70 saturation and -10 lightness was applied on blue channel. Edited in Gimp.

BTW, don't treat this as final output I'd use. Rather an example how basic color manipulation may change image (and it takes just few seconds).

[harvey]

Thanks for the suggestions. In the end I just wrote my own filter to "pull" the lightness towards some value.
Probably as best as you can do for this problem.

[01af]

In the end I just wrote my own filter to "pull" the lightness towards some value. Probably as best as you can do for this problem.

In German language, we call this "shooting cannons at sparrows" ... how do you say that in English?

I guess the easiest way to handle the job would be this: Create a luminance mask by selecting the Channels palette and left-clicking on the image's RGB icon*). Then duplicate the image onto a 2nd layer. Add a layer mask to the new layer using the option "Hide Selection." Change the new layer's blending mode to "Screen." Select the layer mask and, using a large brush, paint everything black that's not sky. Increase and fine-adjust the layer mask's contrast using Levels or Curves, if required. Adjust the layer's opacity level to reduce the effect, or duplicate the layer again to increase the effect if required.

That should take no more than ten minutes or so to do. This technique is called, "let the image edit itself." See my quick-and-dirty attempt below. More fiddling with Levels would get rid of the residual polarizing in the middle of the upper edge.

-- Olaf

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*) This obviously doesn't work anymore in CS4. Instead, in the Layers palette click on the dotted circle icon at the bottom to create the luminance mask.

[jcoffin]

I was interested in the article "Faking a polarizer using RAW" on photoclubalpha.com but I have the opposite problem. How do I balance out a sky that is too uneven due to a part of it being more affected by use of a polarizer?

Here is an example image to show the problem:

[ image elided ]

I have Photoshop CS2 and the closest I can get is by using the replace color image adjustment but it is not very good. I'm wondering if I need a filter that would lighten/darken or saturate/desaturate towards a chosen reference.

Any suggestions on the best way to do this?

Harvey

Best is hard to say. One possibility is to select the sky area (probably with the magic wand), then create a new adjustment layer of the "Invert" type (checking the box for "use selection to create layer mask", or whatever it's called) and with the blend style set to "luminosity". With its opacity set to 50%, you'd get precisely uniform density throughout, with some gray toward the center where it was almost black, blending to a uniform blue for the rest. Chances are you still want some variation in density though -- at something like 30% opacity, it looks to me like a fairly believable approximation of a normal blue sky.

Then again, I live at high enough altitude that my "normal blue sky" is probably a bit darker and more saturated than most people's, so further adjustment may be needed. Once you've used this layer to get the uniformity about right, you may want to add another hue/saturation layer to reduce those as needed (for me, saturation at -12 and lightness at +24 looks more like I expect at somewhat lower altitude, but this is going from memory, so it's probably quite a ways off).

Looking at the preview, it looks like I missed selecting a small rectangle of the sky at the bottom, right-hand corner of the clock, but this should still be enough to get the general idea.