We'll use an Adjustment Layer again - either continuing to work on our image with a Brightness and Contrast adjustment layer on it, or you can open a copy of the original abbey image and follow the steps below.
This time we are going to use the image's histogram - or Levels. This is a graph of the range of tones in the image, which can be controled, adjusting all three (RGB) layers at once or each individual layer. To continue to work on
the abbey image adjusted in the previous task, turn off the Brightness/Contrast Adjustment Layer in the Layers palette.
Otherwise, open the original image again and f ollow the steps below to see how it works:
Open the abbey image on the left (by clicking on the image or the link on the left to open the full resolution version). Remember that it will open up a larger version in a new window. Right click on the larger version and choose 'Save image as' from the drop down menu. Save it in your working images folder or on your USB stick.
When you have downloaded the image, start Photoshop and use FILE > OPEN to locate the image and open it.
Now add an Adjustment Layer by using the 
icon at the bottom of the Layers palette.
This time, add an Adjustment Layer, but choose 'Levels' from the flyout list.
In this dialogue box, you will note that there is graph showing the range of tones (by default in all three channels together RGB).
Grab the middle 'slider' (circled in red) below the graph and move it to the left, until the gamma reading (highlighted by the red square) is around 1.9 to 2.0. Notice how the shadow areas have been improved.
You might want to try moving the sliders at either end of the graph to see what effect they have.
The image can be further adjusted more subtly by adjusting one colour channel at a time.
If you select the Red channel in the drop down list at the top, then use the slider at the right hand end (circled in red), and move it to the left you will reduce the output of red in the highlight, thus making the sky bluer.
Don't forget to save the retouched image with a new file name and then create your evidence sheet with both versions on the image.