Advanced techniques in MaxIm DL include Digital Development Processing and Deconvolution.  These are powerful algorithms for enhancing deep-sky and planetary images.

Digital Development Processing

Digital Development Processing (DDP) is typically used on deep-sky images which have a wide range of brightness.  DDP is ideal for processing images of galaxies which have bright cores and faint spiral arms.  It works by compressing the range of brightnesses between the bright and dim portions of an image.  This is similar to stretching or log scaling, but DDP seems to be the most successful routine and offers quite a bit of user control.

Above:  An image of the Whirlpool Galaxy.  This image is a median combine of three 700-second exposures.  It has been dark subtracted but otherwise unprocessed.  Compare this to the final DDP image below.

To run DDP on an image, select Filters > Digital Development from the main menu, or click the DDP button on the toolbar.

Above:  The DDP button in the fourth on the filter toolbar.  It looks like a little roll of film with 0s and 1s on it.  Very cute.

This will open the Digital Development window.  This is similar to some of the other filter windows discussed in the Filters section. Here you can select the parameters which will affect the DDP output.

Above:  The Digital Development window set for a mild FFT low-pass filter type, auto background, and a mouse-selected mid-level.

How DDP Works

Digital development is a combination of gamma stretching and unsharp masking.  (See also these two methods under the Stretching and Filters sections.)  Gamma stretching compresses the dynamic range of the image, allowing both bright and faint details to be displayed simultaneously.  This is ideal for galaxy images but also works well on certain bright nebulae and globular star clusters.  At the same time, DDP sharpens the image using the preferred unsharp mask technique.  Unsharp masking works by creating a blurred version of the image (the actual "unsharp mask") and then subtracting this mask from the original to create a sharper image.

Digital Development Settings

There are a number of parameters which can be adjusted in the Digital Development window, but only one is really critical for achieving impressive results.  The filter settings control the unsharp masking portion of the algorithm.  This is less important as sharpening can always be applied later.  What we're really after with DDP is squeezing faint spiral arms and bright core detail out of a single galaxy image.  This is where the DDP Parameters come in.

Filter Type

Just as with the Unsharp Mask command, you can select a type of low-pass filter to be applied to create the blurred image mask.  FFT gives you the most control, allowing you to select from the FFT Hardness controls to set the strength of the filter.  Basic kernel filters may also be selected.

FFT Hardness

This controls the strength of the FFT filter for the unsharp mask.  Mild produces the most subtle effect, while Hard gives the strongest filtering.  Mild is the recommended setting as the sharpening process is not the most critical aspect of the DDP method.

DDP Parameters

These are the important settings.  Background sets the new background value in the final processed image.  It is usually sufficient to set this to Auto and let the software select the appropriate value.

Mid-Level is the critical setting and usually the only one which is ever changed from the default.  While there is an Auto setting for this parameter, it is highly recommended that you use the Mouse setting and manually select the Mid-Level from the image.  Use the preview image to determine the effect on the final image.  In the Whirlpool Galaxy image above, the background values are around 150, the brightest portions of the spiral arms are around 250, and the center of the core nearly 1100.  Typically, selecting a region near the brighter spiral arms produces good results, but some experimentation is necessary.

Tip:  Making sure the Digital Development window is selected (and not the main image), you can adjust the Screen Stretch to control the preview image.  The default screen stretch for the preview image almost always looks atrocious and nothing like the final image, so adjusting the preview stretch is recommended.

Above:  The Whirlpool Galaxy after DDP processing.

Another Example

Below are images of M106 before and after DDP.  Using the Information control in MaxIm DL, the background values were determined to be around 2000, the bright spiral arm areas about 14,000, and the core is actually saturated at 65,535.  The Background was set automatically and the Mid-Level was mouse-selected as about 14,000 or so.

Above:  Before and after images of M106.  The left image is a composite of six 60-second exposures, summed together but otherwise unprocessed.  The right image is the same picture after DDP processing.  More core detail is visible in the right image and fainter spiral structure is apparent as well.

Next, Deconvolution Processing...

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