Color burn ink in Photoshop layers
The clouds were moving very fast yesterday. I took eight shots--normal exposures, each about 30 seconds apart. Then I brought each photo into one photoshop file as a layer. Each layer got its own hue. And then each layer was set to color burn.
Even though the movement of the clouds isn't apparent, as I was hoping; the colors that came out are really neat. It's also cool how the NBC Tower got a very high contrast.
Here's one of the original eight photos: