The Arithmetic Operations allows the user to perform operations on one or more images.  In addition to the operations that can be made between the bands of the images, it is also possible to apply gain and offset to the images. Some standard operations are defined in the interface:

• Gain * Image A + Offset

• Gain * (Image A + Image B) + Offset

• Gain * (Image A - Image B) + Offset

• Gain * (Image A * Image B) + Offset

• Gain * (Image A / Image B) + Offset

• (Gain * (Image A - Image B) / (Image A + Image B)) + Offset

• (2 * Image A +1 -  (((2 * Image A + 1) * (2 * Image A + 1)) - 8 * (Image A - Image B))) / 2

It is accessible through:

   Processing → Raster Processing → Arithmetic Operations...

1. To use predefined arithmetic operations click on the icon . 
2. Set the layer and correspondent bands and enter the gain and offset values
3. Click on the OK button. The complete operation formula will be presented in the field below. 
4. Check in the Normalize box and output values normalization will be performed to fit into the output raster values range.
5. Select the output pixel data type or leave as UNKNOWN_TYPE to use the same as the input raster.
   
6. Repository - Select one type of repository by clicking on the button to save the output layer as a file or on the button to save it in the database.
7. Click on the OK button to start the operation.