how to adjust exposure in java?

Question

I want to adjust exposure of an image using Java. I know in Java 2D there are existing functions doing this job. But I also want to know how it works on color level. I did some research online and it says we can multiply R,G,B with certain parameters to achieve overexposure, what are the parameters? and how about underexposure? Thanks in advance!

Answer 1

You might find this page useful, has some quite detailed information on generic exposure functions:

• http://dlraw.sourceforge.net/ExposureFunction.html

In general however, exposure adjustment is all about shifting the colour curves using some form of smooth monotonic function what maps the range 0..1 to the same 0..1 range:

• It needs to be monotonic (always increasing) so that lighter areas stay lighter than darker areas after the transformation
• It needs to be smooth so that you don't create sudden jumps / banding in colour gradients
• It needs to act on the range 0..1 since that is where your (normalised) RGB colour values are!

A simple example of such a function would be:

new component value = (old component value) ^ k

Here a parameter value of k>1 would darken the image, k<1 would lighten the image. You can play with the parameter and the formula until you get an effect you like.