One of the standard first operations that you might perform on a photograph is to apply auto-levels. Aperture makes this easy, and it’s become almost a reflexive action for me. Usually, I almost use the Luminance auto-levels tool as that fixes up levels without affecting the overall color balance of the photograph. However, there are lots of situations where you have a photograph with a color cast and want to quickly remove it. In many cases, using the RGB auto-levels tool is just the ticket.
For example, I’m going to show you an aerial photograph I shot recently on a trip. This is how it looks in Aperture on import with no adjustments made to it:
You’ll notice that I’ve added the histogram to the photograph so that you can see what’s going on with the image. Now, here’s the photograph after using Luminance auto-levels:
This is quite a bit better, and you can see the difference in the histogram, but there’s still a pretty extreme blue cast to the overall picture caused by the altitude. So, the next thing to try is to use the RGB auto-levels tool. Here’s the resulting image:
That’s quite a bit closer to something that I’d want to have as a final result. To be sure, there’s a bit more that I’d do to this image, but at least I have a quick start on it. To see the differences in the images more clearly, here are two detail crops. The first is with Luminance auto-levels, and the second is with RGB auto-levels:
Be sure to try out both kinds of auto-level tools when you’re dealing with a tricky photograph. The results can be quite good and can quickly help you to get in the ballpark of where you want to take your photograph.