The left half of this image is a raw scan of a slide with very large dynamic range.  Part of the image is too light, and the rest is too dark.  The image also has an overall blue cast, either from lighting conditions, or auto color correction by the scanner software.

As you can see, there is hidden detail both in the shadows of the foreground and the sky and mountain area in the background.

Getting  from one to the other is called color correction.

The image was corrected as follows:

1. Sharpen using your favorite method.  In this case, to preserve the original image, I created a sharpening layer using overlay mode, and the high pass filter (tutorial on this someday)
2. Select the sky with the magic wand
3. Create a new curves layer for the sky - PS will create a layer mask that matches the selection.
4. Create a new curves layer for the remainder of the image, and supply it with an inverted layer mask.   
5. The blue cast was removed using the pathway as a neutral reference.
6. Touch ups included cloning some dust from the sky, and blurring the layer masks where sky and buildings meet.

For more details, download the PhotoShop file:

full size (2.1 meg), or half size (.5 meg).  

To download the image, you may need to right click on the link, and specify a place to save the .psd file on your hard drive.