Colour Correction

The Internal Viewer contains a colour correction feature which was designed to correct photographs in a way that simple RGB adjustment cannot. The Colour Correction palette can be displayed from the viewer by pressing the Q key. The palette contains two tabs:

• Remove Cast allows you to remove colour casts.
• Change Colour is an experimental feature and will not be described in this version of the documentation.

Remove Cast

This function allows you to remove colour casts of the kind that are caused by photographic dyes changing with time. It is not uncommon when looking at old colour photographs to see that the darker areas have developed a colour cast. Here is such a photo:

Simple RGB adjustment cannot correct the orange colour cast because it is not constant across the whole picture. The darker areas have been affected more while the lighter areas have hardly changed. PMIO can correct this colour cast by allowing you to adjust the shadow and highlight independently with a smooth transition from dark to light.

Remove cast controls

How to remove a colour cast

To remove colour casts of this nature, proceed as follows:

1. Open the image in the Internal Viewer.

2. Press Q to open the colour correction palette. The Shadow button should already be depressed. This means the palette is ready to accept the shadow colour.

3. Select the shadow start colour by clicking on a shadow area of the picture on the right of the palette, in this case the orange colour that you are trying to correct. A good place to sample the shadow is the pupil of the eye or a piece of clothing that should be black. In this case we will use the eye pupil.

4. Notice that the shadow start colour now shows the colour you clicked and the shadow target colour shows the colour it will be changed to. Drag the shadow target slider to the left to decrease the brightness of the shadow so more contrast is achieved.

5. Click the Highlight button so the palette is ready to accept the highlight colour, and then click the brightest area of the picture on the right, in this case the sweater. As you can see, there is not going to be much change in the highlight, but you might like to move the highlight target slider to the right to increase the brightness.

6. Click Apply to update the image in the viewer. Notice that the preview on the right of the palette now changes as the same settings are reapplied to the now corrected picture. The preview always shows what will happen if the Apply button is clicked.

Zooming the preview

This facility uses a floating palette which means you can still click on the viewer while it is open. This allows you to change the selection in the viewer while experimenting with the colour controls. You can use this to zoom in the preview.

Once you have finished with the zoom you should click on the image again to remove the selection unless you only want to correct the selected area.

Locking the target

When you select a start colour, the target colour is automatically set to the greyscale value of the start colour. It is possible to lock the target colour by using the lock tool button. When a target colour is locked, you can still change it but PMIO no longer updates it automatically.

See also:

The Internal Viewer