Tutorial by Robin Whalley - www.lenscraft.co.uk (Updated May 2012).
A great sky can help make a great landscape photograph. Sometimes though, even when the sky looks good to the eye, the camera just doesn’t do it justice. You may well have been frustrated by this yourself and despite using ND grads, the sky just doesn’t have the impact you had hoped for. The answer is to use Photoshop to create a digital ND graduated filter.
Step 1 - Open Your Image
Open your selected image in Photoshop. My starting image which has a nice sky but it really needs to be darker and more intense.
Step 2 - Quick Mask Mode
Click on the Quick Mask icon in the Photoshop tools pallet. This looks like an oblong with a circle in the middle and is located towards the bottom of the pallet. Click the icon once to put Photoshop into quick mask mode. If you click it again you will return to the normal editing mode.
Step 3 - Gradient Tool
Select the Gradient tool from the tools Pallet. We will use the gradient tool to create the graduated area that you see on ND Grad filter as it transitions from dark to clear.
Step 4 - Check The Gradient
Check the Photoshop toolbar at the top of the screen to ensure your Gradient tool is correctly configured. The gradient needs to be from Black to Transparent. The option to “Reverse” the gradient also needs to be checked.
Step 5 - Draw Out The Gradient
You now need to drag out a gradient on the picture from the sky down to the ground. Do this by clicking on the sky and continue to hold the mouse button down as you drag down. As you do this you should see a line appear showing the length and direction of the gradient. Image this as placing the dark part of the graduated filter over the sky and the clear part over the ground.
Step 6 - Mask Created
When you release the mouse to complete your gradient Photoshop will create the Mask. The sky should be clear but the ground should be red as shown in this screen shot. If it’s the other way in your image you need to check the "Reverse" option in the toolbar by returning to step 4 above.
Step 7 - Leave Quick Mask Mode
Click on the Quick Mask icon again as you did in Step 2 above. This will return Photoshop to the normal editing mode. When you do this you should see the selection you have created surrounded by "marching ants".
Step 8 - Duplicate The Layer
Next create a duplicate layer containing just the area selected. The easiest way to do this is by pressing the J key on the keyboard while holding down the Ctrl key (Cmd key on the Mac). You should see a new layer containing just the selected area appear in the Layers Window.
Step 9 - Change The Blending Mode
In the Layers window you should now change the "Blending" mode from "Normal" to "Multiply". As you do this you will see that the sky become much darker and more intense.
Often when you use this technique you will find the effect is far too strong. If this happens reduce the opacity of the new layer in the Layers Window.
Here is the finished edit showing a sky with much more impact. I have made the image a lot stronger than I might usually in order to demonstrate the technique.
This technique works well with virtually all images where there is some detail in the sky but it is too weak to provide impact.