RegiStax, by Cor Berrevoets, is another great freeware program for high-resolution planetary lucky imaging.

RegiStax 6 Splash Screen with credits.

For lucky image processing, RegiStax performs these main functions:

• Analyses and grades frames to pick out the sharpest ones
• Multi-Point alignment aligns features in individual frames
• Stacks multiple frames to improve the signal-to-noise ratio
• Sharpens with wavelets

We will cover the basics of RegiStax 6 here. Explaining every feature of the program is beyond the scope of this section. Indeed, it might require a whole book to cover RegiStax in its entirety.

Processing Planetary Videos in RegiStax

RegiStax will not work with MOV files out of DSLR cameras. They must first be converted to AVI files that RegiStax will open. We discussed converting MOV files to AVI format previously.

You start with the tab at top left, and work through the buttons under each tab from left to right. Then do the next tab.

1. The Select Tab

RegiStax open file dialog box.

• Open Files - Clicking the Select Tab will open the File Open dialog. Navigate to the file you want to work on and click on it. You will see a preview at right in the window. Open the uncompressed AVI video file in RegiStax 6. If you are using a series of still images, you might have to drag them from Windows Explorer into RegiStax, the open file dialog doesn't work from inside of RegiStax with a series of still image files.

2. The Align Tab

RegiStax Align Tab with align points set in the image.

• Click the Set Alignpoints button at top left. You will see the alignment points appear in the image.

• Minimum Distance Between Alignpoints Settings

  • For planets like Mars and Saturn set to its lowest value of 10.
  • For Jupiter, set to 15.
  • For the Sun or Moon, set to 30.

• Intensity Selection - Normally set to default, but images with large black areas of sky, use 3x3 area or Lowest pixelvalue.

• Adjust the number of align points with the Number of Alignpoints slider. Eliminate weak align points by moving the slider to the right. If you are doing planets with black sky in the frame, make sure none of the alignpoints are in the blank sky or near the edge of the planet. Remove alignpoints by right-clicking on them.

• Click the Scan Frames button. This will scan the frames and pick the best frame on which to base the registration of the rest of the frames.

• Set the Limit Setup at lower left. This specifies how many frames will be used in the stack, and the method that the frames will be aligned. You can specify an exact number of frames, or a percentage of the total.

  Limit Setup Options

  • Lowest Quality %
  • Best Frames %
  • Frames/Apoint
  • Best Frames

  Lowest Quality % and Frames/Apoint will use the best individual frames in the stack for each alignpoint. Each alignpoint will have its own set of frames. Bart Declercq, RegiStax expert, advises users to "never use Lowest Quality % as an option, since it causes RegiStax to use a different number of frames for each alignpoint - which usually leads to tears and suffering."

  Best Frames % and Best Frames specified by a total number of frames will use only the best overall frames. The same frames will be used for each alignpoint.

• Click the Align button.

  After setting the Limit Setup and clicking the Align button, the frames will be sorted by quality. The slider that runs along the bottom will now be set to reflect the frames selected for stacking (to the left of the slider's location) and those excluded (to the right of the slider's location).

  The current frame number for the end of those frames selected for stacking (in this example, frame 1891), and the number of frames to stack compared to the total number are also displayed (in this example, 250 frames out of 3,559 total). You can manually slide the slider to the left or to the right to exclude or include more frames if you desire.

• Click the Limit button. Then go to the Stack Tab.

3. The Stack Tab

RegiStax Stack Tab - After setting the limit setup and clicking the limit button, RegiStax will look like this. The lines coming from the alignment points show the direction of drift between images.

• Click the Stack button. The number of frames that you specified in the Limit Setup will now be aligned and stacked.

• Click the Save Image button. - Name the file and save it in your working directory.

4. The Wavelet Tab

RegiStax Wavelet Tab - Wavelets apply sharpening to details in an image based on their size.

• Check Automatic at the top of the wavelets panel so changes will be applied automatically after each wavelet is adjusted.

• Check Linear for the Waveletscheme.

• Select Gaussian as the Wavelet Filter type.

• Adjust wavelets - This is usually done by trial and error. The settings will vary depending on the subject, and the quality of the stack. If you check Automatic at the top of the wavelets panel, changes will be applied automatically after each wavelet is adjusted.

• Check Use Linked Wavelets. There are three adjustments you can make for each wavelet layer. Adjust each to taste.

  • Amount Slider
  • Denoise
  • Sharpen

• To reset the wavelets, you can click the Reset Wavelets button at the top of the Wavelets panel, or you can right click on an individual wavelet slider.

• Do All - After you have adjusted the wavelets, click this button at the top left to apply the wavelets to the image.

• Save Image with a new file name.

Hold your mouse cursor over the Saturn image to see a comparison of the stacked image to the wavelet sharpened image.

5. Additional Adjustments There are now a number of additional adjustments that you can make to the image under the Functions Panel under the Wavelets Tab, such as aligning the RGB channels, denoising and deringing, cropping, resizing and adjusting the color, brightness and contrast. A common adjustment that needs to be made to many planetary images is to align the channels. In the example of Saturn above, a red fringe can be seen on the bottom edge of the planet, and a green one on top. This is caused by prismatic atmospheric dispersion. Use RegiStax's RGB Align function here and click the Auto button to correct this defect. It can also be a good idea to monitor the histogram for the image while sharpening with wavelets. Some adjustments can lead to clipping of the highlight details. If this happens, try lowering the contrast slider in the Contrast and Brightness section. After making these adjustments, don't forget to save the image with a new file name.

RegiStax Adjustments Panel

Tips

• You can tell how good the image is by what level of wavelet sharpening reveals details. A really good image will look better after sharpening level one.

• Too much sharpening causes ringing artifacts around limb of planet.

• You need to stack more frames of Saturn because it is faint and usually a bit underexposed. Underexposure leads to a poor signal-to-noise ratio. Stacking more frames improves the signal-to-noise ratio.

• You can save a number of particular wavelet settings for easy re-use.

• If you have several videos or sets of images to process, RegiStax also has a batch processing function under the Tools menu.

• If you have a fast computer with lots of time on your hands, try upsampling the image before aligning and stacking.

Problems with Seams

A problem image showing "seams".

Sometimes when you use RegiStax you may find that the final stacked image contains seams between areas of the multi-point alignment that makes the image look like a puzzle. This may be because the image moved around due to poor seeing or tracking, or because of brightness variations due to clouds, or variations in transparency. To reduce or remove seams there are several different things you can try.

Align Tab

• Use the Best Frames limit setup option.

• Use the Alignpoints slider to reduce the number of alignment points.

• For planets, try using Align by Center of Gravity.

• Pre-filter the images before Scan Frames and Align

  • Click the Pre-filter Active box at top right.
  • Check Blur Radius and set to 2 to 3.
  • Check Smooth. Leave at the default of 15.
  • Check Normalize.

• Increase the alignment box size under Settings > Advanced Controls.

• If you still get seams, activate Show Alignpoints and hover over the seams to see which alignpoint is responsible, and then go back to the Stack Tab and remove those align points and re-stack.

Stack Tab

• Check Correct Geometry.

• Check Normalization of frame intensity.

This tutorial was done with RegiStax version 6.1.0.8.