Levels allows you to alter various aspects of an image. You can (auto) set the white and black points, or pass a curve to use, along with specific channels to act on. By default it acts on all colour channels together.
- Act on the red channel.
- Act on the green channel.
- Act on the blue channel.
- Auto adjust levels to fit. This forces the colours in the image to fill the whole range; that is, the lightest colour is set to white and the darkest is set to black.
- Auto adjusts the black point to fit. This sets the darkest point in the image black.
- Auto adjusts the white point to fit. This sets the lightest point in the image white.
- --black <n>
- Set the black point to the value given (between 0 and 1).
- --white <n>
- Set the white point to the value given (between 0 and 1).
- --curve <c>
- Set the curve (though it is only currently implemented with linear interpolation). The argument should be passed as a list of
point,value pairs delimited by spaces, for example:
0,0 33,40 66,60 100,100.