How to Process an ISS Transit of the Moon

Although ISS transits are rare for a given location, on a global scale they are not rare at all. Every day and night the ISS is passing over somebody’s head multiple times a day and they will pass between the earth and the moon, somewhere.

How I got an Apod: Read Dylan’s planning and acquisition for the ISS transit of the moon.

I captured the ISS nicely on a single RAW frame (which you can download here), I wanted to give it a little extra care to process well. I also wanted to share the photo quickly to share the “moment” with the world so it was processed and released within 2 hours of its capture.

Described here is the workflow I’ve used to re-process the photo for this article.

My ISS APOD submission was roughly the same process, but I encourage you to modify the steps as you feel fit. Every photo is different! It’s a long process for an otherwise simple photo but gives you an idea of the journey the image takes from RAW to finished.

For me, seeing the moon in its natural, but enhanced, colour is just wonderful. It reveals a structure and composition of the moon that is hard to impart with the moon’s regular monochromatic tones. To do this we need to increase our signal-to-noise ratio (SNR) so that when we increase the saturation, we don’t also increase the ISO/heat/read noise the frame contains. This is achieved with stacking multiple different exposures of the same target. So we’ll stack all the exposures of the moon framed nicely and overlay the single exposure with the ISS in the exact position it was captured.

Processing the RAW frames

Step 1) Collect all your exposures in a folder. Include the exposure(s) with the ISS and also the ones without. We’ll need those to stack together.

Step 2) Open all exposures in Adobe Bridge and select them. Right click and open in camera RAW (or do the following steps in Lightroom or whatever you process your RAW files in).

Step 3) In Camera RAW, press “Select All” to affect all your exposures with the same settings.

Step 4) In the “Detail” tab, turn Noise Reduction to 0. Stacking will achieve most of this and the rest can be done later.

Step 5) Back in the “Basic” tab, I like to hit “Auto” to see how the application suggests changes. It tends to neutralize the colour and correct the exposure computationally. Because I purposely underexposed for lower noise it automatically corrected this by dragging the exposure up. Then you can use your own artistic license to drag the sliders around how you prefer. See figure 2 for the settings I used.

Step 6) For my photo I dragged the highlights low, the whites high, and the shadows roughly in the middle. I also dragged the saturation to 100 and the vibrance up a fair bit. This makes it a bit noisy, but we’ll deal with this later.

Step 7) Hit “Save Images… “ and save them somewhere as uncompressed TIFs. I just save them in the same folder with “1 Digit Serial Number” numbering. They end up as 1.TIF, 2.TIF, etc.

Using AutoStakkert!2 (AS!2)

Step 8) (optional) Resize all your images to 3000 pixels wide so AS!2 doesn’t crash or run out of memory. The fastest way to do this is to create an action in PhotoShop or Bridge and batch run it across all of them, but I won’t describe that step by step. You can do it manually if you need to. NOTE: If you have enough processing power and memory to avoid this step you might be ok to skip resizing down. For me, AS!2 can’t handle such big files yet.

Step 9) If you work on an Apple Mac like me, now is the time to grit your teeth and jump over to Microsoft Windows. I know right? Ugh. But we are going to use the amazing application AutoStakkert!2 (download here). You’ll need to edit the AutoStakkert.ini file in the same folder as the application and change the MaxWidth and MaxHeight numbers to 9999 to handle the size of your files.

Step 10) Open AutoStakkert!2, then drag and drop all your TIF files onto the OPEN button.

Step 11) Change the Image Stabilization to “Planet (COG)” so AutoStakkert!2 will detect the boundaries of the moon for alignment. If your image does not include the moon’s boundaries you may need to try “Surface” instead.

Step 12) Click “Analyze,” and wait. It takes a lot of memory and pixel crunching! This will computationally grade the quality of each exposure and give you a graph you can use to judge how many of them you should use in your stack. Generally, I use the best 50 – 75%. I chose 75% for this photo. The graph makes a lot more sense with 1000s of video frames, but it gives a good general idea even with a few DSLR exposures.

Step 13) Go to the main image preview window showing the 100% zoom of your image and change the AP size to somewhere between “100” or “200” since these are large images. Then click “Place AP grid”. The window will fill with alignment squares and a total “APs” number will be displayed in the top left. If there are more than 1000 you might want to increase the min brightness and hit “Place AP grid” again. The more alignment points there are, the longer this next step will take.

Step 14) Tick the box that says “Sharpened” and if you’d like a 50% larger image you can also choose “Drizzle” 1.5x.

Step 15) Hit STACK! Go do your tax return. This is going to take a while…

Step 16) You should now have two files in the subdirectory below your files that AS!2 has placed there. One is the regular, noiseless TIF and the other is a super sharp convoluted TIF ending in _conv.TIF. We are going to blend these to add some sharpness to the image. Open both of these files in Photoshop.

Editing

Step 17) On the sharpened TIF, select-all and copy. Then make the other unsharpened TIF active, and paste. Now you have two layers, with the sharpened one on top. Change the blend percentage to 30%, or tweak as desired.

Step 18) Use the crop tool or selection tool then image-crop at this point to shave off any rough edges or excess from the stacking.

Step 19) Open the TIF with the ISS with it from the multiple exposures you have and copy-paste into the new working document as a new layer. You may need to change the blending and nudge the layer around so the surface details match and the ISS is in the exact location. Add a layer mask and invert the mask side of the layer so none of that layer shows, then using the pencil or brush tool paint the ISS area of this layer back into view. You’ll need to zoom in and get pretty precise with this so you don’t have fuzzy edges and artifacts where the two layers meet. Toggling the mask by alt-clicking the layer mask really helps see what you’re doing as you do this.

Step 20) Add contrast to the ISS layer (Image -> Brightness / Contrast). You can make this layer a smart object and apply the Brightness / Contrast as an adjustment filter within it if you don’t want to apply a destructive contrast.

Step 21) Add a Hue/Saturation adjustment layer under the ISS layer, but above the moon layer. Increase saturation until the moon’s colour is bright, but not too bright. Putting this adjustment layer below the ISS layer prevents the ISS from getting colour noise. It’s a shadow anyway in this example.

Step 22) Add a levels adjustment layer at the top and bring the black point slider further towards the middle to give the moon and the blackness of space more contrast. I also reduced blue slightly and increased red a fraction in levels. Adjust to taste.

Step 23) Add a brightness / contrast adjustment layer and also increase contrast. This adds to the crater and surface definition.

Step 24) At this point the image has a fair amount of noise, especially the colour “flecks” from the severely increased saturation. You can apply some noise reduction here to smooth this out a bit. I recommend the Topaz Denoise Photoshop plugin. Also you should duplicate the original 2 moon layers (smooth and convoluted), and merging into a new single layer for the noise reduction. Turn off the originals by clicking the eye icon next to each layer. That way your original stack data is not destroyed as you apply noise reduction.

Step 25) Copy the ISS layer in the same way and turn off the original layer, then apply the exact same denoise parameters to it for consistency.

Step 26) Since everything we’ve done is non-destructive, we can now go back and tweak the various adjustment layers as you’d like.

Step 27) Save this file and flatten all the layers. Save this flattened version as a new file. Since we haven’t used any calibration frames like Darks or Bias it’s also important to zoom in and use the spot-healing tool to clean up any hot pixels or colour artifacts that the increased saturation may have introduced.

Step 28) We’re done! My final step is always to add a small amount of sharpening, either with the Smart Sharpen or Unsharp mask. Remember to set the Radius to 1 or less in these tools and only do this after you’ve resized the image to the size it’s meant for – wallpaper screen size, social media sharing sizes, or print.

Still with me? Gosh, I know that was long-winded, but hopefully the result is worth it. All of these steps created the final image you see here, processing is vitally important for an award winning image.

The final file can be downloaded here at its maximum resolution and is licensed Public Domain for anyone who would like to use it for any purpose.

Take care and clear skies!