Gamma is a display of the contrast of an image represented by a graph. Traditionally, the vertical axis represents the output values, with the lowest point being the shadows. The horizontal axis represents the input values, with the leftmost point representing the shadows.
In a perfect theorhetical image, every input value would map to exactly the same output value. If you drew a line from each input and output value and marked where they intersected, then connected all these intersection marks, you'd have a perfectly straight line at a 45-degree angle. The gamma (or "slope") of this image would then be "1", since every input value devided by the matching output value would be 1 (any number divided by that same number is 1).
If you were to change the input or output values in such a way that the slope of the gamma curve (actually a line in this theorhetical example) were to be more than 45 degrees you'd be increasing the contrast uniformly across the entire brightness range of the image. Likewise, if you were to change the values so the slope was less than 45 degrees you'd be decreasing the overall contrast.
In the real world, most values are in the mid-tone areas, so we seek to give them good contrast for differentiation. Highlight and shadow areas are flattened to compensate, since we're less sensitive to those areas.
A graphic representation of an image with a higher midtone contrast and lower shadow and highlight contrast would resemble the letter "S", so the most common gamma curve is known as an "S curve".
When you use your image editing program to adjust "curves", it is the gamma curve you are adjusting. In other words, you're adjusting (actually remapping) the output values against the input values.
In a perfect theorhetical image, every input value would map to exactly the same output value. If you drew a line from each input and output value and marked where they intersected, then connected all these intersection marks, you'd have a perfectly straight line at a 45-degree angle. The gamma (or "slope") of this image would then be "1", since every input value devided by the matching output value would be 1 (any number divided by that same number is 1).
If you were to change the input or output values in such a way that the slope of the gamma curve (actually a line in this theorhetical example) were to be more than 45 degrees you'd be increasing the contrast uniformly across the entire brightness range of the image. Likewise, if you were to change the values so the slope was less than 45 degrees you'd be decreasing the overall contrast.
In the real world, most values are in the mid-tone areas, so we seek to give them good contrast for differentiation. Highlight and shadow areas are flattened to compensate, since we're less sensitive to those areas.
A graphic representation of an image with a higher midtone contrast and lower shadow and highlight contrast would resemble the letter "S", so the most common gamma curve is known as an "S curve".
When you use your image editing program to adjust "curves", it is the gamma curve you are adjusting. In other words, you're adjusting (actually remapping) the output values against the input values.
Comment