I think all the value inputs (with numbers) desaturate, only the color inputs pass the color data, so just plug the image into the bump input and adjust the value. If you want a negative image use a math or colormath node, set to subract your image from one or white.
The gain function is the easiest way to adjust the contrast. .5 is no change, zero results in .5 gray, 1 is on or off if the input is greater, or less than .5 (on or off instead of white and black because the colormath node handles red, green and blue independantly).
You can adjust an exploding displacement map with a subtract node.
Be sure to open the previews the results can be easily viewed.