Facebook applies a curve + gradient mask to cover photos. Makes the bottom 1/3 of those photos darker, presumably to make the white user name and link buttons that are overlayed on the cover photo easier to read. Otherwise the name and link buttons might disappear on a very high key photo.
Nobody likes that. Lot's of complaints. Lot's of requests for an option to turn it off, but Facebook ignores such trivial user requests. So why not edit cover photos by applying a reverse curve + gradient mask? Make the photo lighter on the bottom so when Facebook makes it darker it will look like the original.
I've loaded a series of blank grayscale images as Facebook cover photos and measured the resulting RGB values inside Facebook. That gives me a rough idea of what kind of curve and gradient mask they use. The gradient mask is easy, but I'm stumped over how to build a curves adjustment to inverse the effect of Facebook's adjustment.
I've Googled "inverse curves" and got a few hits that seem to say it can't be done. Simple experiments prove that it's not a simple task. Anybody know any tricks?
Here's the rough Facebook curve I get using my grayscale images.
Input>Output: 51>20, 102>50, 153>76, 204>104.
That's a strange looking curve, so using only 4 points is probably not very accurate. If I can solve the inverse curve problem I'd use more points.
I'm not much of a Facebook user, but several people are using my photos for their cover. Many look bad, so I"d like to find a way to give them a version better suited for their cover.
