# Add / Subtract Constant Operator

Use an Add/Subtract Constant operator to add a positive or negative grey value to each pixel in the grey-scale image, generating an image artificially lighter or darker than the original. Adding a value artificially brightens an image:

You must also choose whether pixel values that fall below 0 or exceed 255 are clamped to these values or are allowed to wrap around from those limits. For example, if you allow values to wrap then a pixel with a grey value of 200 that has the value of 100 added to it has the new value of 45 (200 + 100 = 300; 300 - 255 = 45). If you choose to clamp the values then the same pixel does not exceed 255 after the operation.

Applications that use an Add/Subtract Constant operator typically use it as a sub-step in some more complicated process rather than a useful operator in its own right.