'Levels'

Clive R. Haynes FRPS
 

We've seen what happens when the 'black' and 'white' ends of the 'Output' (printer) 'sliders' are adjusted.
So let's see what happens if we make a dramatic change to the setting. This will help to improve the understanding about how the adjustments work.

 
Above:The result of crossing the black and white slider controls over so that the printer is instructed to print black as white and white as black - the result? A negative image.
The blacks are printing as white and the whites are printing as black and the intermediate grey tones are 'reversing' along the way. Plus, as were working in 'RGB', the colour content also becomes a 'negative'.
 
Adjusting the Colour with 'Levels'
So far we've only adjusted the 'Levels' by using the composite RGB 'channels' for the image. By clicking on the drop-down arrow in the 'Levels' dialogue box we can select either R, G or B - that is Red, Green or Blue. These represent the three 'channels' which make up the colour component of the image. If we select one, say,'Blue', we can make changes which are target at the Blue Channel only. See the example below:
 

Above: In this example, the mid-point 'slider' has been pushed to the darker end of the gradient scale and the Blue Channel content is become more blue.
What happens if we push the Blue Channel content the other way?
 

Above: Here's the answer - the mid point has been moved to the lighter end of the gradient and blue is removed from the image. The result is a 'negative blue' - that is to say the opposite colour to blue, or as we say the 'complementary colour to blue - which is yellow and here it is.

We therefore have the ability to change colour shift by adjusting 'Levels'. This is something we'll explore as it can help with correcting for a 'colour cast'. Go to the next page.....
 
To discover more about 'Levels' - click the link below

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