Highlight/Shadow Action

In this sample, we can see the early morning light has caused deep shadows in and around the rider and the horse. The image requires post processing to bring out the shadow detail and improve the exposure of the image.
This is the final result of the process. We want to lighten the shadows to bring out the obscured details however, we want to do this in such a way as to make the image natural. My general workflow for these type of images is to do all necessary post processing to improve levels, exposure and in this case improve the dark shadows. However, in situations like this, we will introduce noise to the image as we try to improve the exposure in the shadow areas. This will have to be dealt with and the process described in this articvle will touch on my process.
One general note here that most advance Photoshop users already know is to use adjustment layers for all corrections. Not only does this protect the orginal image data, it allows for fine control over the final adjustments using the  opacity and fill controls. I actually find using adjustment layers allows me to make radical adjustments, many times simply using Photoshop defaults and then I can fine tune and dial in the adjustment by lowering the opacity or fill levels. It actual makes work much faster. 
This image shows the layers I create to adjsut the sample image.
First step is to run the shadow/highlight adjustments. I have created an action that runs this process. 
The action follows these steps.
1.) Makes a new adjustment layer to apply the shadow/highlight filter. As the filter can not be applied to transparent adjustment layers like levels, curves etc. we need to create the layer with editable data. First the action create a new transparent adjustment layer, named "Shadow/Highlight - Shadow Bias". You can name your layers anything you wish. Then we merge all visible layers and make a copy into the new layer. As we do not want the Merge Visible Layers to flatten the image, we can bypass this by holding down the "ALT" key while selecting the Merge Visible Layers from the layer flyout menu.
2.) We then select the new layer and run the Shadow/Highlight filter.
The settings I use are pretty basic. As I am using adjustment layers I tend to only use the defualt setttings as they seem basically adequate for this purpose. The image is then fine tuned by adjusting the opacity layer. The only setting changes I have made is to set the highlight amount to 0% thus having the filter effect the shadows only. I do this as my highlights are improved and usually recovered when I run the NEF raw image file through Camera Raw. If you are using JPG, then you would be better to leave the default settings to apply the filter to both shadows and highlights.
After applying the filter, you can fine tune the settings with the layer opacity levels. If you are going to create an action to batch run on filters you may want to have the action apply a generic layer opacity level. You can always go back and fine tune it after running the batch action.
When running the Shadow/Highlight filter, unfortunately noise is introduced into the image particularly in the shadow areas. This needs to be dealt with and the second part of this article deals with the noise issue. A word of recomendation, I would complete all final post processing prior to running the Shadow noise routine as additional noise may be introduced.
The noise routine follows the following steps.
1.) Another adjustment layer is created and named "Shadow Noise". Again the layer can not be transparent so again we "Merge Visible Layers" while holding the "ALT" key in order to copy all visible layers to the new layer.
2.) You then apply a noise removal routine. You can use a Guassian Blur, noise removal actions, or noise removal plug-ins. In my case I use Neat Image plugin in the action to remove the noise. Again because the layer is adjustable, I tend not to get too worried about the level of nosie removal being too heavy. This part of the routinine will be specific to your application.
3.) Now we have the noise cleaned layer but it is applied to the entire image. We only want the shadow areas to be cleaned leaving the remainder of the image untouched. To do this we need to aply a layer mask. As we want the underlying layer to be seen in all areas of the image except the shadows, we need to make a black mask with the shadow areas painted in white to apply the noise reduction to the shadows only.
First we need to select the shadows. We do so by using Select>Colour Range and choose the Shadows from the drop down menu and hit OK. 
IMPORTANT - We need to invert the selection.
Then we return the layer with the selection made. As we want the mask to be black so as to show the underlying image data, we click the Mask button at the bottom of the Layer Pallet while holding the "ALT" key. This create a black mask and fills the selection with white thus creating a mask that allows the noise reduction to be applied to the shadows only.
After finalizing the routine, we can fine tune the adjustment by adjusting the opacity of the Noise Layer. 
Thats about all. The two routines can be created as actions and run as an automated batch.
Hope this process is helpful.