The term ‘Tonal Range’ is also sometimes referred to as ‘Dynamic Range’ or simply the distribution of light and is used to describe the quality of colour and tone in an image, ranging from the darkest to brightest area and everything in between. Simply stated, the Histogram in cameras and processing software provides a graphical representation of the Shadows, Midtones, Highlights (SMH) of an image.
The Shadow areas are on the left, Highlights on the right and the Midtones in between the two; At either extreme is pure black and white.
Many local processing functions are targeted at the SMH to achieve their result.
Other processing functions, eg: curves, levels etc may be used to target the more complex Shadows, Low Midtones, High Midtones and Highlights (SLMHMH) to achieve their desired outcomes.
In the example, the curve is pulled down to darken the shadows and low midtones and pushed up to brighten the high midtones and highlights.
Darkening shadows and brightening the highlights is essentially adding contrast.
It is one thing to talk about tonal ranges but to understand how a particular process could affect an image one must be able to recognise those ranges. Whilst there is plenty of material on the internet regarding tonal ranges we have created an SMH guided exercise and an SLMHMH guided exercise which we think will help you better understand them. There are also two opportunities for you to test your understanding.