Photoshop
Tutorial
Tutorial #10
Selective Exposure Adjustment using Layer Masks
However hard we try to obtain a balanced exposure in-camera there will always be a time when the contrast in a scene is too much and selective areas of the image either need to be lightened or darkened.
As an example, here is a shot of the Iron Bridge in Shropshire. It was taken quite early one August morning but already the Suns intensity has created a large black shadow on the right-hand of the footpath.
Traditionally the dodge and burn tools are used for selective exposure adjustment - and these tools are fine when only a minor adjustment of a small area is required. But these tools are just too inaccurate for large areas that require a big adjustment in exposure.
Here is the image with the shadow lightened using the dodge tool at about 20%. It's certainly an improvement over the original but notice how the lightened area now looks a little 'washed out' and false. Also the process needs some skill and patience to prevent a 'banding' effect from the brush strokes.
What we are going to do now is to create a new curves layer above the original and then adjust the exposure of that entire layer until the shadow area on the right is improved. Obviously the rest of the layer will then be drastically over-exposed and so we will then use a layer mask to remove the over-exposed areas revealing the original image below.
Open the original image in Photoshop. Create a new 'curves' adjustment layer by clicking the 'Layers' tab, then 'New Adjustment Layer', then 'Curves'.
If you look at the histogram on the curves grid you will see a pronounced peak towards the black end which has been caused by that heavy shadow. Click-and-hold on the curves line corresponding to the peak and drag the mouse forwards to increase the exposure of the shadow area to a point that looks improved. Remember, we are not trying to remove the shadow entirely - just to make it less pronounced but retaining a natural look.
When you have found the point that gives an improved exposure of the shadows without it looking too false release the mouse button. You will see that the rest of the image is now drastically over-exposed but don't worry - we will rectify that shortly.
If you look a t the 'Layers' panel at the bottom-right of the screen you can see the original image is called 'background' and the new curves adjustment layer is called 'Curves 1'. Contained within is a white box called a Layer Mask Thumbnail. This thumbnail gives an indication of how much of that layer is visible:
All white = all off that layer is visible - nothing can be seen of any other layer beneath it.
All black = None of the layer is visible - the layer beneath is now seen in its entirety.
So you can see that if we can have some of the Layer Mask Thumbnail white ( = visible) and some of it black (= layer below visible) then we can combine the original image with the adjusted image to create one good one.
How do we do that? Simple - we just paint on the layer with a black brush to reveal the layer beneath and (if we make a mistake) a white brush to paint it back again.
First you need to make sure that Photoshop's foreground colour is black and its background colour is white (since these are the only colours we need to use).
If not, click on 'Default Foreground and Background Colours' (or just press 'D' on the keyboard). This will actually give the exact opposite of what we need initially so then click on 'Switch Foreground and Background Colours' (or just press 'X' on the keyboard).
Top Tip !
Just press 'D' on the keyboard to revert to the default foreground and background colours
Now we are going to paint black onto the over-exposed parts of the curves adjustment layer which will reveal the correctly exposed 'background' layer beneath.
Choose the 'Brush' tool and then the 'Brush Preset Picker'.
The exact type and size of brush will depend very much on what you are painting and the level of detail required. You will probably change brushes during your work, as we will do here. Although the brushes I use here can be used as a guide, it does eventually come down to preference and experience.
Note that the brush size required also depends on the size of the image you are editing. The image size used in this tutorial is a RAW image with dimensions 3800 x 2600 pixels. If you are editing a smaller image than smaller brushes will be required.
First we are going to paint black around the edge of the shadow area. Therefore we need a fairly small brush with a very soft edge so that we don't end up with a black band as we touch the edge of the shadow. However, too small a brush will be very difficult to handle accurately.
From the 'Brush Present Picker', adjust the Master Diameter to 200 px and the Hardness to 0 % (or just pick the 'Soft Round 200 Pixel Brush' from the presets box).
Very carefully paint the over-exposed area around the edge of the shadow. Use small strokes and initially work a little distance away from the shadow to get the feel of the brush. Slowly work towards the edge of the shadow to achieve a good blended edge.
If you make a mistake and paint on a section that you want to remain lighter, then click on 'Switch Foreground and Background Colours' to make the foreground colour white and then paint over the mistake. This will re-instate the lighter layer.
Top Tip !
Just press 'X' on the keyboard to switch the foreground and background colours.
Remember to switch colours back again afterwards so that black is the foreground colour.
Once you have finished going around the entire edge of the shadow you now want to paint over the rest of the over-exposed area of the image - but don't just pick the largest brush available straight away otherwise mistakes can be made. Work up the sizes.
Increase the Master Diameter to 400 px and change the hardness to 100% and paint around the section you have already done to widen it (now that you have painted the edge detail you don't need a soft edged brush any more)
You can now either continue to fill in the rest of the over-exposed area with this brush size or increase it again for speed.
Use the Layer Mask Thumbnail as a visual guide to how much you have painted over - useful for checking if you've missed a bit.
Once competed, we can now edit the photograph in the normal manner confident that the composition isn't dominated by that black shadow.
Roll mouse over image to see original version
As you can see, Layer Masks are a very powerful tool for making selective adjustments - and very easy to use. In this tutorial we were using them to adjust the exposure of a shadow area but they can be used in many other ways including selective saturation adjustment, colour popping, and even to remove unwanted people from street scenes.
In the next tutorial we will edit the same photograph - but this time using the Shadow/Highlight tool. A slightly more specific tool but a much quicker method to reduce the effect of shadows in an image or in a back-lighting situation
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