How to enhance image according to a transformation function

Hi guys,

I am new to Matlab. I wanted to design a GUI that allows me to enhance a color image. I wanted to map the image according to a user input piecewise function that he clicked from the graphing axis.

for eg. the original image pixel value 5 enhanced to value 7, value 10 to value 13 etc. according to a linear plot.

Any advices on how i could do it?

Please help me! Any advice will be appreciated!