Image Adjustment in Material Editor

Hello guys,

I am searching for way to modify images and textures through material instances. What I have right now is a vertex paint material, and through CheapContrast RGB and Multiply I modify the colors of the current texture.
But it’s a really low quality, and I dont want to necessarily mess with the contrasts of the textures. I would really like simple Levels, or Gamma, like in Photoshop. But I don’t seem to find a way to do so.
Is there some node, or some guide somewhere to point me in the right direction?