The Color panel

The central control panel for manual, semi-automatic and fully automatic operations is displayed after an image has been loaded.

It shows histograms of the counts of red, green and blue pixels from the original image and a number of trackbars, option buttons and a check box.

With no correction applied, the left and right images will be identical, and all trackbars will be at their default positions.

You can modify the brightness and contrast of each colour component separately. For example, with the Brighness button (default), the colours may be shifted independently:

The change will be applied immediately to the right image.

You may also change the contrast of each colour separately either prior to or after a brighness change:

Gaps may appear in the histogram of the modified colour, since the bins of the histogram have discrete values, but contrast modification is a decimal multiplier. 

It may sometimes be necessary to reduce the brightness of a colour after increasing its contrast.

If you wish, you may modify all three colours simultaneously by checking the RGB box and dragging the lowest trackbar in the desired direction:

If you wish to reduce yellow stain manually, you may drag on the Semi-automatic trackbar at the bottom of the colour panel:

If you apply any of the automatic options from the main toolbar, the effect on the histograms will be shown when the operation completes. Here for example, you can see what the Automatic Colour Equalization (ACE) option has done to the image and to its histograms.

If you apply a subsequent automatic treatment step, in the case below, an automatic setting of the gray point, the result will also be shown immediately: