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PhotoShop 4 Beginners Levels and Curves - part 2 of 1 2

by Mike McNamee Published 01/08/2010

An advantage of using the clipping warning is that it is independent of the screen calibration and even on calibrated screen it is not possible to set the levels as accurately by eye as compared to using the numerical values. Leaving a small highlight area clipped will not necessarily deface an image but if the area is of any size in an inkjet, you will find a large 'bald' patch devoid of ink which will be rather obvious, especially if the print is viewed from an angle.

CLIPPING

In an RGB image the pixel colour values in each of the red, green and blue channels range from 0 to 255 units. Thus 255 in the red channel is as red as it is possible to obtain; 255 in both the red and the green channels is as yellow as it is possible to go; 255 in all channels delivers a full white. At the other end of the scale values of zero are zero values in the channels and zero in all three delivers a fully dense black.

The concept of clipping may be explained as follows. Imagine you are photographing a door with a milk-bottle on the step (very English!) and in sunshine (only sometimes English!). Correctly exposed, the whitest part of the milk-bottle should register values of at or very slightly below 255 units in all channels. An increase in camera exposure would lighten most of the image but when it came to the milk-bottle there would be nowhere to go as it is already at 255 units. We say that the milk-bottle is 'clipped'

Areas within a picture that are clipped will not have any ink laid down by an inkjet printer, they will be pure paper white and may also be visible as bald patches if the print is viewed at an angle. A well-adjusted image, therefore, will have all whites that require any detail to be set at a level just below 255 units - 252 or 253 would be typical. Conversely, at the shadow end, blacks at 0 RGB units are fully dense black with no detail and if detail is required in the shadows, values of at least 15 RGB points are normally required. Just as with highlights, any parts of an image which are 'darker' than 0 units are 'clipped' to zero.

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1st Published 01/08/2010
last update 09/12/2022 14:57:54

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