When I'm shooting outdoors I almost always have a polarizing filter on on my lens. A polarizer is one of the most useful tools available for a landscape photographer. It cuts the glare off water surfaces, windows, and other reflective surfaces. It can cut the glare and darken leaves and flowers. It gives a sky that rich blue color and makes clouds really pop. The best part is the effect is adjustable. Turn the filter to increase or decrease the polarization effect to get it the way you want it. It's my favorite tool when shooting landscapes.
I don't use many other filters because you can simulate them when editing the images later, but a polarizer is not so easy to simulate. If you have glare on water, windows, or leaves there's not much you can do about it after you take the photo. It's always best to get the best image you can in camera and don't rely on post processing to fix problems later.
There is one polarizer effect that you can simulate in post processing and that's the blue skies. I do this is Lightroom sometimes if for some reason I didn't have the polarizer on or didn't get the effect I was looking for. I do this by using the Hue, Saturation, Luminance sliders.
I want to reduce the luminance (brightness) and increase the saturation of the blue part of the sky, without impacting other parts of the photo. To do this I select Saturation and click the round target icon just under the word Hue. I then use my mouse to click and hold in the blue part of the sky. While holding the left mouse button down I drag the mouse up to increase the saturation of the color I clicked on. You can manually move the blue slider but the color of the sky is often a combination of Blue, Aqua and even some other colors. Using the target allows you to select the exact color combination you want to adjust.
Likewise, you can click the Luminance and repeat the process to reduce the brightness to get the effect you want. Be sure to cluck the Done button when you're finished.
The two photos above are before and after I adjusted the saturation and luminance of the blue portion of the sky. This pretty closely matches the effect you get from a polarizing filter. Of course you might have problems with this technique if you have other blues in the photo that are close to the color of the sky. I suggest trying this out. Just be careful to not over do it.
If you have Nik Color Efex software you can get a similar effect using the Polarizer filter. Here's the same photo with the polarizer applied in Nik Color Efex
The Nik software has a rotation slider simulating the effect of turning the polarizer filter to adjust the effect. Again, be careful to not over do it.
These are a couple quick techniques to fix the sky if you didn't have a polarizer when you took the image. Don't rely on this and other post processing adjustments. Try to make the best photo possible when you take the shot. You'll get consistently better photos every time.
Several people commented on my last post. Thanks for letting me know what you think. I love hearing from you and welcome questions or criticisms. Let me know what you think and if you found this useful.