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178 Chapter 9 Primary In
Image Contrast Affects the Operation of the Color Balance Controls
There’s another reason to expand or otherwise adjust the contrast ratio of an image
before making any other color corrections. Every adjustment you make to the contrast
of an image changes which portions of that image fall into which of the three
overlapping tonal zones the color balance controls affect (covered in the next section).
For example, if you have a low-contrast image with few shadows, and you make an
adjustment with the Shadow color balance control, the resulting correction will be
small, as you can see in the following gradient.
What Exactly Is Image Detail?
Image detail is discussed frequently in this and other chapters, mainly within the
context of operations that enhance perceived detail, and those that result in the loss
of image detail. Simply put, image detail refers to the natural variation in tone, color,
and contrast between adjacent pixels.
Because they occur at the outer boundaries of the video signal, the shadows and
highlights of an image are most susceptible to a loss of image detail when you make
contrast adjustments. This results in the “flattening” of areas in the shadows or
highlights when larger and larger groups of pixels in the picture are set to the same
value (0 in the shadows and 100 in the highlights).
It’s important to preserve a certain amount of image detail in order to maintain a
natural look to the image. On the other hand, there’s no reason you can’t discard a bit
of image detail to achieve looks such as slightly crushed blacks, or widely expanded
contrast for a “high-contrast look” with both crushed blacks and clipped whites. Just
be aware of what, exactly, is happening to the image when you make these kinds of
adjustments.