…continuedHow to Process Planetary Images
Although I may be finished with RegiStax, additional processing often can improve my image further. I next open the wavelet-sharpened image in MaxIm DL. Here I rotate and resample the image, as well as apply a few iterations of deconvolution. I prefer to perform the rotation and resampling here rather than in RegiStax, because MaxIm uses a powerful bicubic algorithm that interpolates neighboring pixel information to create a smooth resized image. I find these modifications should be done before further processing, because resampling at the end of my routine usually results in a softer final picture. I usually resample my images to about 150% of their original size, which seems to produce a smoother final image and helps me to avoid overprocessing.
If I used a color camera, I split the image into its red, green, and blue (RGB) components, then manually realign them on a surface feature rather than on the limb using the Process > Align pull-down menu and align using the Overlay option (6). In addition, I sometimes use one of the monochrome color channels that displays the most detail and use it as a luminance image. This is often the red channel, so the resulting color combination will actually produce an “RRGB” image. If I used a monochrome camera, I convert the individual R, G, and B images to monochrome (RegiStax saves all TIFF files as color images), align them on a surface feature, and color combine them.
At this point, I again save the image as a 16-bit TIFF and make a duplicate for further processing with a deconvolution filter. I generally use the Lucy-Richardson filter in MaxIm DL (Filter > Deconvolve), choosing the Extract by Mouse Click option in the Noise Extraction Tools and selecting 16 background points to map the noise level of the image. My next step is to manually input a PSF (point spread function) Radius to properly apply the deconvolution (7).
Most deconvolution algorithms require a point source to be sampled directly from the image to get an accurate reading, but photographs of the planets are exposed for too short a duration to record stars. I specifically use MaxIm DL because it allows me to input my own PSF radius and experiment until I find one that works well. Generally I select a PSF radius between 1.0 and 2.0 pixels, then apply two iterations of deconvolution (8). The Lucy-Richardson algorithm has an advantage over unsharp-mask sharpening in that it can bring out fine details while suppressing noise. This routine should be gently applied, however. I often achieve good results by repeating the process a second time using a different PSF radius.
Once I’m satisfied with these results, I save the file (again as a 16-bit TIFF) with a new name and open it in Adobe Photoshop CS2 for final adjustments such as color balance, saturation, and noise reduction if needed. I generally touch up the image’s brightness, contrast, and color balance by making a Curves layer. Again, I try to avoid clipping the histogram. Finally, I carefully inspect the image for detail and grain. If necessary, I’ll apply a mild high-pass filter to add slightly more contrast, or a median filter to reduce any unwanted residual noise. Now I consider my work done, so I save the image in Photoshop Document (PSD) format. Before I can share the image via e-mail or on a website, I must flatten the layers (Layer > Flatten Image) and convert the image to 8-bit data (Image > Mode > 8 Bits/Channel), finally saving it in JPEG format.
Remember that this advice is based on my own telescope, camera, and seeing conditions, so my preferred settings may not apply perfectly to your situation. Experiment with these settings to find a routine that works best for you.
The planets are always changing, so imaging these bodies can be a very rewarding experience. While capturing and processing planetary images can be time consuming, the result has scientific value. Even in this exciting age of solar-system exploration by spacecraft, amateurs still can make significant contributions to planetary science. With today’s steady improvements in both cameras and software, I’m sure that the amateur’s place in planetary astronomy is secure for many years to come.
Donald C. Parker has been photographing the "major" planets for more than 30 years, including one that became a dwarf.