Setting the Tone

Usually subtle changes are used to improve an image rather than major alterations to save a badly taken photo. Some of the illustrations used here are extreme to make a point.

Many tools are available PSP X2 is used here but applying the techniques is similar in most graphic programs.

Restrict changes to areas by selecting them or using a mask.

In general, look at the image carefully and assess what is needed and before making an adjustment, try and predict the outcome.

Tonal range of an image is measured in 255 steps with the blackest tones at 0 and the brightest at 255. An overexposed - washed out or too light - image has the darkest tones higher than 0 and an underexposed - very dark, dull or lifeless - image has the brightest tones at less than 255.

The histogram shows the amount of information spread over the tonal range and where there is no information there is no detail available.

Curves, Levels and Highlights / Midtones / Shadows adjustments all work by changing the values of the steps in the tonal range.

Levels

Dragging the RHS slider in to the left of the Levels adjustment for the underexposed image makes all the tone levels at the top of the range bright and gives some washed out areas as in the sky shown below. All the tones are made lighter and you can see some detail.

In the over exposed image (below), moving the left levels slider to the right makes the dark levels ie the shadows, darker. All the tones are made darker.

Moving the centre slider changes the values of the mid tones.

A high contrast image has bright highlights and dark shadows – a full range histogram – and moving the centre slider exaggerates either one or the other.

Curves

The Curves adjustment allows you to be more selective and if a Curves adjustment layer is used it remains editable while the file is in *PSP format.

Any point on the straight diagonal line depicts the current value of that tonal range in this image. Moving it up will increase it and down decrease it and sideways moves that value to a new position. As a point is moved, adjacent values will be altered too.

When using the Curves dialogue box, check the top part of the box,

Use the maximise button to get a good view of before and after images. Using “Preview on Image” uses a lot of computer processing power as you make changes and can slow you down.

Use the zoom and pan tools to focus on an area.

The diagrams show the main action of moving different points. Click on the line to create a point and move it to alter that part of the tonal range.

1) To brighten the highlights

2) To darken the highlights

3) To brighten shadows

4) To darken shadows

Where the curve is steeper the contrast is higher and where it is shallow, the contrast is less

5) To increase mid tone contrast and decrease the highlight and shadow contrast.

This gives an “S” shape and seems to be the commonest adjustment made. The graph shows a steeper curve in the midtones and shallow curves in the shadow and highlight regions.

6)  To increase the highlight and shadow contrast and decrease the midtone contrast.

Open an image, assess what you want to happen and then try these movements.

The Highlights / Midtones / Shadows adjustment

This only allows three adjustments but is often very effective as is shown in this very dark cliff face.