Next Challenge: Atmosphere
This illustrates the difference in just presenting the data and what it means to take a careful human approach to pulling the data out to maximize its impact.
The entire Rosette Nebula showing the difference between a simple "one-click" stretch of the data and hours of careful processing.
This is a extreme close-up of the Rosette Nebula. You can see that in the simple stretch by the computer there is much less detail that where I've carefully processed the data.
The movement of the earth and noise in images are universal problems astrophotographers and the challenges are met with math and machines. The next challenge is biology: the human eye. Even with big telescopes, objects in deep space are dim. The difference in brightness between empty space and a few glowing hydrogen atoms is very small. Computers have no problem reporting these brightness values as different but the human eye cannot easily make these distinctions. This means that my images, even after I've collected hours and hours of photons are very dim. In order to take detection from the level of the machine to the human I need to "stretch" the data. See the example of the pre vs. post stretch of a bit of sky around the Triangulum Galaxy. Stretching the data allows eyes to make out the faint stars and structures.
It's at this moment that the scientist and the artist diverge. Up to this point I've merely collected "data" using machines. I now exit my role as a technician and become an artist. This is the stage of the process that takes the most time and is the most challenging. The goals and methods I use change depending on the subject. One maxim that guides my processing is that I stay true to the underlying data. What you see is what is up there in the sky. However, in the process of getting to a final image thousands of small decisions will add up to dramatically different outcomes for an image. It’s during this process that I bring my sensibilities and skills to the table in order to bring out detail in a particular object or highlight an aspect of the scene that I find appealing. You can see a couple of examples on this page of a simple stretch of the image by a machine. These are very different from the much more complex and subjective process I employ in working with the data.
What a image looks like before and after it is stretched. Stretching is required so the human eye can see the differences in gray levels.