Here is an example of our current Twitter header image, compared to the image we actually uploaded:
See how much brighter the image uploaded is than what Twitter displays? In fact, it’s strategically brightened to make the most of what Twitter does to the image.
Twitter darkens the lower portion of bright images uploaded to make the white text stand out. So you don’t want to brighten the center, lower portion of images. In fact, we darkened the middle, and lightened the lower corners (as well as brightening overall).
Of course, different types of images can withstand different treatments. Our goal was to make the image look as much like the original as possible, while allowing for darkening to make the white text stand out.
Here’s a comparison between our original image (bottom), and how it looked after we adjusted it (top) before uploading:
See how much we brightened the lower corners, but actually darkened the center slightly? (I also darkened the center part of my shirt, but failed to save the “before” look). That helped the center white text stand out, but kept the image more normal looking after Twitter darkened the whole lower half. Without the corner brightening, the image looks odd after Twitter darkens everything in the lower half.
However, darkening and lightening should be relatively subtle, or the image will start to appear a bit strange. Experiment to find the right balance.
How To Test Changes Privately
While I went ahead and changed the actual image on our account several times, what many accounts do is create a new Twitter account to test their image on, and then just delete the account, or use it for some other purpose when you’re done testing your header image uploads.
Just make sure to create only one account, as Twitter doesn’t like to see too many accounts created from the same IP address in a short period of time. (If you do need to create multiple accounts, use this tip.)
Problems to Watch Out For
Currently, images display differently on mobile devices than on Twitter.com, so if you want to integrate your avatar, for example, it won’t look like it fits on some mobile devices. Also, if you’re not familiar with image editors, be careful when darkening or brightening that you don’t create white areas (blow out highlights) or lose details in shadows to solid black.