I know I can get contrasted colour by Colour::contrasting(), but I am drawing juce::Image so I wonder is there any easy way to change the contrast of drawn juce::Image all whole juce::Component?
For any help great thanks in advance.
You might want to look into juce::Component’s setComponentEffect method.
It allows you to write an effect class that can manipulate all the pixels drawn by a Component directly. Maybe not the most efficient method, but you can create a class derived from ImageEffectFilter that adjusts the contrast of you component. If you need to change your contrast dynamically, this can do that. If not, I’d recommend just using the colours you want to have directly, since that will lead to better performance.