Ever the realist, Dave had a backup plan and introduced the group to a technique becoming popular particularly amongst portrait photographers, frequency separation.
There are a multitude of commercial programs available to enhance portraits which unless used with great care, result in images looking like waxwork models devoid of detail and character and bearing little or no resemblance to the original subject.
Frequency separation helps make retouching a portrait easier and results in an accurate representation of the model making him or her look real, alive and fresh. Frequency separation works because it allows you to separate the texture of an image from the tone and colour.
Dave started his presentation with a demonstration of how an image of an average person can, by careful manipulation be transformed into a glamour model totally unrecognizable from the original.
He then explained that frequency donates the levels of detail in an image. High frequency being the fine detail such as grass, hair, grains of sand, stone textures and low frequency being the broad sweep of colour and tone like sky, soft clouds and marshmallows.
Using the layers facility in Photoshop, he demonstrated the technique of separation, splitting the image so that the colour and tone are on one layer and all the texture detail is on another.
Utilising an image of a young adolescent couple he showed how, with a few minutes of effort it was possible to correct the tone and colour layer before adjusting aspects of the texture layer before finally merging the layers into a final accurate image which retained the characteristics of the models whilst removing or minimising the temporary blemishes that all teenagers suffer at that age.