Exposure and Density controls
Exposure and Density are a good way to prepare your image for further correction with 3-Way Correction, Secondary stage, or Master Curves. In the Primary stage, you will typically run Auto Balance before correcting with Exposure and Density. This page covers both controls and gives a comparison example in order to explain them better.
Exposure
Exposure stretches or compresses the Red, Green and Blue channels. Value range is -16 to 16. Default setting is 0. The practical range is -2.0 to 2.0.
Exposure is good for setting the overall brightness of the image. Use Exposure when you just want to add a bit of exposure compensation after adjusting other controls (like 3-Way and Saturation). You can use the 3-Way Highlight control to similar effect, but you may already have used that to set white balance.
The Exposure control works just like exposure compensation on a camera, with the slider calibrated in f-stops. Setting the Exposure value to 1 will raise the exposure by 1 stop, doubling the brightness of the image. Setting the Exposure value to -1 will lower the exposure by 1 stop, making the overall image half as bright. The black point always stays the same but the values above black stretch or compress to increase or decrease the perceived brightness.
For fine tuning, you can dial in small increments of Exposure compensation by using decimal values. A value of 0.25 or 0.333 will correspond to a 1/4 stop or 1/3 stop exposure change. You can dial in any decimal value between -16 and 16, but typically, small values will allow you to brighten or darken your image in a natural way.
Technical Note: Working in floating point in your native application will change the way the Exposure values shift. If you are in 32-bit mode, then colors are not clipped at white but instead you get out-of-range values above 1. If you are in 8-bit or 16-bit mode, then colors will get clipped at black but not at white.
At left, Exposure at 0, the default setting. At right, the Levels filter in After Effects shows a histogram of the RGB values.
At left, Exposure at -1. At right, the Levels histogram shows the RGB values compressed towards black.
At left, Exposure at 1. At right, the Levels histogram shows the RGB values compressed towards white.
Density
Density shifts up or down the value ranges for the Red, Green and Blue channels. Value range is -16 to 16. Default setting is 0.
Decreasing the Density shifts all the RGB values towards black and clips those values to black. Moving the Density below 0 recenters the values, and gives more room to work in the top range whites. Negative values stretch toward black, giving more detail and contrast in the highlights and less contrast in the shadows.
Increasing the Density shifts all the RGB values towards white and clips those values to white. Moving the Density above 0 recenters the values, and gives more room to work in the top range blacks. Positive values stretch toward white, giving more detail and contrast in the shadows and less contrast in the highlights.
In the Primary stage, Density is used for larger shifts, and can be used to shift the color values in preparation for later steps in the color treatment process. Secondary and Master Density are used more for fine tuning areas of the image.
Technical Note: Working in floating point in your native application will change the way the values shift. If you are in 32-bit mode, then colors are not clipped at white but instead you get out-of-range values above 1. If you are in 8-bit or 16-bit mode, then colors will get clipped at black but not at white.
At left, Density at 0, the default setting. At right, the Levels filter in After Effects shows a histogram of the RGB values.
At left, Density at -1. At right, the Levels histogram shows the RGB values shifted towards black, and any values less than 0 are clipped to black.
At left, Density at 1. At right, the Levels histogram shows the RGB values shifted towards white, any values greater than 1 are clipped to white (except in floating point projects).
Comparison of Exposure and Density
Sometimes it is difficult to see the difference between Exposure and Density. Since these parameters are important first steps in your color treatment, especially in the Primary stage, we wanted to explain them further with a comparison.
Exposure creates more natural results. The image looks brighter at high values or dimmer at low values, as if under a bright light or viewed in a dark room.
In contrast, Density is shifting values and is useful for changing the operating value range of the image. High negative values will create hard silhouettes. High positive values give the appearance of the image shot under a flash.
Exposure at -4, Density at 0. At right, After Effects' Levels histogram shows the RGB values.
Exposure at 0, Density at -4. At right, After Effects' Levels histogram shows the RGB values.