Noisy images are a challenge to process because the image’s signal can often be close to the noise level, making it difficult to smooth out noise while retaining detail in your image.

MaxIM DL has limited options for dealing with noise, mostly limited to low pass filters. This article walks you through processing a noisy image using MaxIM DL.

Result

This is the image without any processing done on it:

From this image, you can see that it is quite noisy – the background is speckled, and the galaxies are noisy.

This is the final processed image:

The noise in this image has been smoothed out quite a bit and the galaxies remain reasonably sharp. Some more work could be done using Photoshop, Photopea, GIMP, or other image editing software but this is a great start.

The following sections walk you though integration, attacking the noise, and exporting your final image.

Stack and Combine Your Images

The steps in this section have you combine your Slooh.com images into an LRGB image to prepare it for further processing:

  1. Start by selecting from the menu Process – Stack
  2. Ensure that the checkboxes next Object and Filter are checked
  3. Under the Align tab, select Auto – star matching
  4. Add the files from your Slooh.com mission by clicking Add Files, or drag the files over from a Windows Explorer window onto the Stack window in MaxIM DL
  5. Under the Combine tab, select Average as the Combine Method and select IEEE Float for the FITS format
  6. Click the Go button under the Combine tab to align, stack and combine the images

Stretch Your Image and Attack Noise

Now that your image has been combined, you’re ready for further processing and noise smoothing.

  1. From the menu, select Filter – Digital Development
  2. Select None for Filter type and select Auto for both the background and Mid-level in the DDP Parameters area and click Ok to commit the changes
  1. Next, from the menu, select Filter – FFT Filters
  2. Select Low-Pass for the filter type – this type of filter addresses noise in your images
  3. For Filter Hardness, select Custom
  4. Enter or select 1 in the Cutoff field
  5. In the Weight field, enter or select 50 and click ok to commit the change

The noise has been smoothed-out but we can do a little more to make it smoother.

Wavelets are parts of your image that define structures based on pixel sizes. Wavelets allow an image to be mathematically decomposed into layers having different sized structures on them. Noise typically resides and wavelet layers one and two, with the remaining layers having much less noise. The highest wavelet layer is called the Residual layer and has the largest structures on it.

The preceding image demonstrates what wavelet layers one, two, and the residual layer contains. From this, it is clear that noise is at layers one and two with hardly any noise in the residual layer. We use this knowledge to our advantage to smooth out the noise in our image.

We’ll use Wavelets to try to smooth out the noise some more.

  1. From the menu, select Filter Wavelet filter
  2. Select Mexican Hat for the Wavelet Type
  3. Set W1 to about 1.12
  4. Check W2 and select about0.63
  5. Select W3 and select about 1.21
  6. Select W4 and select about 0.94
  7. At the bottom, for Residual select about 1.17
  8. Click Ok to commit the change

Modify The Screen Stretch

Modify your screen stretch to make the background darker (if your screen stretch window is not visible select View – Screen Stretch Window)

Your image still has a little noise in it, but it has been mostly smoothed out. You could continue to process this image in Photoshop or Photopea to try to address the remaining noise and then possibly sharpen the image a little to restore the detail in the galaxies.

Exporting Your Final Image

Use the following directions to export your image as a TIFF:

  1. From the menu select Process – Stretch
  2. Select Linear Only at the top, Screen Stretch in the middle, and ensure you select 16-bit for the output range and click Ok
  3. Select File – Save As
  4. For the Save As Type, select TIFF and for the Size Format option, select 16-bit

Your image is now ready to be imported into Photoshop, Photopea, GIMP, or whatever software you wish to use.

Conclusion

In this article, you learned how to address noise using FFT and Wavelet filters and you learned how to align, stack, combine, and export your final image using MaxIM DL.