I'd like to know how to create the header background in the following image (taken from here). I'm referring to the grid of images behind the search box. Clearly those are just square colored images but with some kind of filter.
I've tried to merge the colored images with a black opacity layer, but that gives a different look. I also don't think it is a blur. I would describe the look as 'softening the image in grayscale'. Please help me to recreate this in Photoshop.