Nikon 9235 Reference Manual - Page 73

Step 4-Setting the Gray Point The point midway between the maximum and minimum input values is known as the "gray point" (or "midpoint"). This point represents a neutral shade corresponding to an output level of 128. The gray point is controlled by a gray-point slider at the bottom of the curve edit display. Moving the gray-point slider to the left increases the brightness of mid-tones without "washing out" details in highlights. Moving the slider to the right darkens mid-tones without obliterating detail in shadows. The Gray-Point Slider The gray-point slider is located at the bottom of the curve edit display. Gray-point slider Gamma value After clicking the slider once to activate it, move it to the left to increase the brightness of mid-tones in the selected channel, or move it to the right to decrease brightness. Alternatively, you can enter a value for gamma directly in the text box under the slider.The effects of changes to the gray point can be seen in the active image. Gamma Gamma (also written " γ ") is a fundamental property of video systems, one that determines the intensity of the output signal relative to the input. When calculating gamma, the maximum possible input intensity is assigned a value of one, and the minimum possible intensity (no input) is assigned a value of zero. Output is calculated by raising input to a power that is the inverse of the gamma value (output = input (1/γ) ). In practical terms, raising the gamma value has the same effect as moving the gray-point slider to the left, raising mid-tone output values and brightening the image while leaving the maximum and minimum values untouched. Lowering the gamma value has the same effect as moving the gray-point slider to the right, lowering mid-tone output values and darkening the image. The default value for gamma is one, which produces a linear curve. Gamma can be set to any value between 0.45 and 3.00. Reference:The Tool Chest 72