Basic Contrast Adjustments

Exposure does have an effect on contrast, but generally it’s governed by the lens, film and lighting.

Contrast can also be controlled through the chemistry, materials, techniques and algorithms used in  processing and printing. Digital images are processed either in the camera or the lightroom, so contrast adjustments can be made at the time of exposure or during post-processing. When you adjust the contrast in a digital camera, you’re altering how the raw image from the sensor is processed just before it’s saved to memory.

Contrast is the relationship between the light and dark tones of an image. The further apart these values, the more contrast or separation the image is said to have.

Vibrancy is an attribute of color that is also related to contrast. Images with more contrast are naturally more vibrant. Generally speaking, a lens with higher contrast will also render more vibrant color. However, digitally, we can control contrast without affecting vibrancy.

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Brightness/Contrast
Perhaps the simplest tool for adjusting contrast is the Brightness/Contrast panel. Unfortunately, it’s also the most misunderstood amongst professional color retouchers.

In earlier versions of Photoshop, B/C was strictly a linear adjustment, however, in recent versions it’s been changed to a gamma adjustment, with a check box to revert back to the “legacy” linear algorithm. Combined with the Luminosity mode and the Blend If sliders, this adjustment panel is an effective means of making basic contrast adjustments.

Dragging the contrast slider to the right lightens the quarter tones and darkens the three-quarter tones, increasing the contrast and vibrancy to an image with a normal distribution of tones. Conversely, dragging to the left decreases contrast and vibrancy. For lighter or darker images, the Brightness slider can be used to vary the “center” of the adjustment, similar to a “parametric” equalizer. This then compensates for high-key or low-key images, and the primary reason these two closely-related adjustments appear in the same panel.

Contrast can be controlled independently of vibrance by using the Luminosity blend mode.

Vibrance can be controlled independently of contrast by using the Color blend mode. When used this way, the Brightness and Contrast sliders each have a different effect on color saturation, without affecting lightness.