StarTools Processing, Spiral Galaxy M51

Overview

This step by step guide details how I processed image data for M51 in StarTools version 1.4.316. I received guidance on processing galaxy images from Ivo Jager the creator of StarTools although any errors on this page are my own.


The image data was acquired using an Planewave 17" Reflector located in Mayhill, New Mexico under dark skies free of suburban light pollution and remotely hosted by iTelescope. The imager is a Finger Lakes Instrument FLI-PL6303E cooled CCD with a 3072 x 2048 pixel array. The image data is luminance only. The data was stacked with DeepSkyStacker. The stack was 7 exposures, 4 minutes each. All DeepSkyStacker image processing options were turned off. The data was stacked using the Kappa-Sigma algorithm with Kappa=1.5 and iterations=5.


AutoDev - Initial Image Stretch

Open
Linear was not Bayered or is whitebalanced
Possible stacking artifacts, OK
AutoDev, default parameters

It can be seen that stacking artifacts, light gradient, vertical banding and noise are present.

Crop - Remove Stacking Artifacts

Although not apparent in the screenshot, stacking artifacts are present along each of the four edges. Generally there will be lines a few dozen pixels in width along each edge of an image as a result of stacking. This step also frames the object of interest in the final image.

X1 = 78 pixels
Y1 = 61 pixels
X2 = 2928 pixels
Y2 = 1932 pixels

Bin - Remove Noise and Reduce Size

Remove some noise in the final image by combining pixels at the expense of image resolution and size. The image size in this case is reduced to 1828x1244 pixels. A combination of cropping and binning can be used to reduce and frame the image.

[(scale/noise reduction 64.16%)/(242.92%)/(+1.28 bits)]

Wipe - Remove the Light Gradient

As can be seen at the end of the prior step, there is a bright light gradient on the left side of the image with respect to the right side.

Tracking active OK
Parameter [Precision] set to [512 x 512 pixels]
Parameter [Dark Anomaly Filter] set to [3 pixels]
Other parameters set to default

Auto Develop - Stretch the Image

This step is difficult to reproduce exactly in StarTools. Drag the transparent green rectangle Region of Interest to cover most of the large part of M51. Some noise at this stage is optimal. The background should not be completely black.

Redo global stretch
Parameter [Ignore Fine Detail <] set to [4.0 pixels]
Other parameters set to default

It is possible to finely tune the stretch with the Dev module by adjusting gamma to increase or decrease dynamic range.

Deconvolution - Reduce Blur

Deconvolution removes blur and sharpens the image in this case the dust lanes become more apparent. After deconvolution, stars should not have an encircling ring. If this is the case, mask each one of the ringed stars in addition to the stars masked by the "Generate mask automatically" option.

Generate mask automatically
Parameter [Radius] set to [2.4 pixels]
Other parameters set to default

Sharp - Enhance Details

Without changing the mask, apply sharpening.

Parameter [Amount] set to [110 %]
Parameter [Small Detail Bias] set to [97 %]
Other parameters set to default

Experiment with setting the Amount parameter higher, my preference for this image was to set it lower.

HDR Reveal - Reduce Brightest Areas

Reduces the bright galaxy core to reveal additional detail.

Clear the mask
Parameter [Algorithm] set to [Reveal DSO Core]
Parameter [Detail Size Range] set to [164 pixels]
Parameter [Strength] set to [1.1]
Other parameters set to default

Experiment with setting the Strength parameter higher, my preference for this image was to set it lower.

HDR Tame

Lightens brightest areas of the galaxy. The effect is small but it tones down the central brightness again and brings out a little more detail in the core.

Parameter [Dark/Bright Response] set to [0.48]
Parameter [Detail Size Range] set to [500 pixels]
Other parameters set to default

Life - Brighten Fainter Areas

This step is subjective but it can add to the aesthetics of the final image by brightening some of the fainter areas. This also brightens the stars. It is possible to avoid brightening the stars with a mask.

Fill mask.
Parameter [Strength] set to [60 %]
Detail Preservation Radius set to [40.0 pixels]
Other parameters set to default

Denoise

Reduce image noise. It is critical to select an appropriate value for Grain Size. I tend to set it higher than the default. If more binning is used in an earlier step, Grain Size can be set lower. For each image, determining the best value for Grain Size takes some experimentation. The outer areas of the galaxy should look wispy, not pixelated. If the outer areas are pixelated, increase the Grain Size value and possibly increase the Smoothness value also. The Grain Size value on the initial Wavelet De-Noise screen establishes a reasonable value for the parameter, only the Grain Size value on the second Wavelet De-Noise screen is used in processing. Grain Size gives StarTools an idea of the image's visible noise grain and doesn't noise reduce details larger than the Grain Size value.

Track
Stop Tracking do final noise reduction
[Grain Size] set to [12.0 pixels]
Parameter [Smoothness] set to [80 %]
Other parameters set to default

Layer - Remove Stray Color

Remove any color that was introduced. I believe this is a bug with the current Alpha version as it introduces color into a luminance only image.

Parameter [Layer Mode] set to [Desaturate fg (Average)]
Other parameters set to default

Contrast

Another optional step is to apply Contrast prior to De-Noise. This step was not included here since this image didn't seem to need further contrast. On most images I use about 50% contrast and set the Dark Anomaly Filter to about 3. The Dark Anomaly Filter causes StarTools to ignore dark pixels during its contrast calculation.

Log File

Each time an image is modified, StarTools logs the operation and associated parameter values to a file. The file is located in the StarTools distro directory.