# KBF00003 - Brightness/Contrast Tool
Instructor : Pradeep Mamgain
Brightness contrast tool is used to adjust the Gain, Gamma, Contrast, Brightness and Saturation of an image.
# Tool Image
# Brightness/Contrast Tool
At the top of the control we have have check boxes for channels Red, Green, Blue and Alpha. Use them to limit the effect of the tool to selected channels. Gain works as a multiplier to existing RGB values. If you slide it to 1.5 and your existing RGB values are 0.5, 0.6 and 0.7; new values would be 0.75, 0.9 and 0.105. The affect of the Gamma slider is non-linear, it does not affect the black and white levels, it just affects the pure gray. You can use it to boost or lower the gray values in your image. Gamma affect is non linear.
Contrast is the range of difference between the darkest and brightest pixels in the image. Reducing the contrast will reduce the difference between the darkest and brightest pixels and vice versa. Brightness affects linearly i.e. it will be applied identically to all the pixels. Slider value is added to the value of each pixel. Saturation controls the amount of saturation in pixels. A value of zero will turn image to grayscale.
Low and High range slider works quite similar to Gain control. If Low is at 0.0 and High is reduced from 1, it would behave like gain slider where its value will be multiplied by the inverse of high value to the pixel values. If High is 0.90 and then each pixel will be multiplied by 1/0.90. When High is at 1 and you increase the Low slider, it pushes image toward black without affecting the whites at all.
Clip Black and Clip White is used to clip out of range colors which are less then 0 pixel value (Black) and grater 1 pixel value (White). It effects only those images having floating point color depth. It has no effect on 8 bit or 16 bit per channel.
When select Pre-Divide/Post Multiply, you force fusion to divide image pixel values by the alpha value before applying color correction and then re multiply the values with alpha channel. This is very useful and when performing an additive merge or when working with CG images generated against black. It is also useful when you have edges around blue/green key, it prevents the creation of illegal additive image.
What is Pre-Mutiplied Image?
The
pixels in the color channels have been multiplied against the pixels in the alpha channel. In a pre-multiplied image transparent pixels are always black. Multiply anything with 0 and what you get is zero i.e. Black.
Now click on the common control 
tab. First option there is Blend. This blend slider is found in all controls except loader and creator tool. This slider is used to blend the input image and tool's final modified image. When you anchor slider at zero your input and output image would be same. Red, Green, Blue and Alpha channels checkboxes are used to limit the effect of the tool to specified color channel.
Apply Mask Inverted, inverts the complete Effect Mask (Inverts all the masks applied to the tool) channel for the tool. Multiply by mask when selected Fusion will cause the RGB values of masked image to be multiplied by the mask channel's value.
Channel and Threshold Low/High will only appear when you connect any effect mask to the image. Use channel drop down list to select the Channel of the input image used to create the mask. Threshold Low/High, can be used to clip the bitmap image. Increasing the Low slider will clip the pixels below the slider's value to zero (Black) and decreasing the high slider will clip pixels higher then the specified value to white.
Use Object / Use Material only works with files which support Material and Object ID channels. Two such formats are RPF and RLA format. It is an advanced topic and we will cover it separately in another tutorial.
#Other Info
# eyeon Fusion KB # Adobe After Effects KB # Autodesk Maya KB # Composting Passes Inside Fusion