This first example will use stacked, colour-converted data from a single Hyperstar frame of the Pleiades. Please download the unprocessed .jpeg file from http://img156.imageshack.us/my.php?image=frame270filessdmaskcropbi9. jpg where you will find an unprocessed image of Merope and its associated nebulosity as the central part of the frame. This image is made up from 70 sub-exposures of 1 minute per sub taken with the Hyperstar/SXV-H9C combination. Having a reasonable number of subs means the final stacked image will have a pretty good signal to noise ratio, although the image may not go that "deep". However I think you will find the image does go fairly deep, as a faint galaxy [PGC1396, mag.17.89] will appear towards the top right hand corner of the frame as you process the image.
Having downloaded the file from the "Image Shack" site, and saved it into a folder on your computer, now open the file in Maxim DL using File/Open. Zoom out once using View/Zoom Out so that you can see the whole frame on your screen.
What we are going to do with this image is to split it up into separate Luminance (L), and Red (R), Green (G), and Blue (B) files. We will then do a little image processing on the L file only before recombining all four files back into a colour image.
With the Pleiades file opened up in Maxim DL, go to Colour/Convert to Mono and click o.k. Save the monochrome image to a new file with the filename ending in MONO.jpg so that you can remember what it is. Minimise the file. Now open the original Pleiades file again and this time split it up into its RGB components using Colour/Split Tricolour and click o.k. You will get three monochrome images appearing on the screen, which are the RGB channels of your data. Minimise these three files. Maximise the MONO.jpg file. We shall now use just button clicks to bring out the faint nebulosity. Go to Filter/Digital Development/FFT -Low Pass/Mild and click o.k. This process will carry out a Fast Fourier Transform low-pass filtering of the data, which will pull out the faint parts of the data (the nebulosity) without completely blowing out the bright parts (the stars). Save this processed file as _MONO_FFT.jpg and open up the Screen Stretch window -View/Screen Stretch. Pull the left tab (red) to the far left and move the right hand tab (green) to about three-quarters of the way along to the right. You will see that the DDP filtering process, like magic, has brought out all the faint nebulosity. We now need to reform the colour image by recombining the LRGB files.
Go to Colour/Combine Colour - conversion type is LRGB, conversion colour space is RGB, tick allow resize and tick Bgd Auto Equalize. Put your _MONO_FFT.jpg file into the Luminance box and put the RGB files into the Red, Green and Blue boxes and click o.k. Save the file as Pleiades_RGB_process.jpg. Close Maxim DL and open up PaintShopPro. Open up your RGB process file within PaintShopPro, go to Effects/Automatic Contrast Enhancement/Darker,
Mild, Bold and click o.k. Save this file as Pleiades_RGB_process_PSP.jpg and you're finally done with this cheap and cheerful process.
Figure 10.1 shows the raw unprocessed data, in 10.2 the DDP processed luminance file, in 10.3 the recombined LRGB file, and in 10.4 the final processed image. I have not cloned out any hot pixels, lens flare or other defects in this simple process. You can take the processing of this image further by doing that, and by carrying out some noise reduction as well as some further contrast enhancement.
PhotoShop Processing of the Pleiades Data and Use of Noel Carboni's Actions
Before we begin there are two things about PhotoShop and astronomical imaging processing. One, PhotoShop is plain scary, it looks big and intimidating and it is big and intimidating. Some people can have a day job based on the fact that they can run PhotoShop - it's that big. The second thing we need to know is the shape of the "Magic Curve" mentioned in the Golden Rules. We shall use a nonlinear stretching routine in PhotoShop called "curves" to pull out the faint stuff in the same way that we used the DDP FFT function above in Maxim DL. However, you need to get the shape of the curve you are going to use correct, or you will blow up the stars as well as bring out the faint stuff, this is where the "Magic Curve" comes in. The shape of the curve can be seen in Figure 10.5. The steep rise at the beginning of the curve is what we are using to bring the faint detail out of the darkness. We then use a second point on the curve (by clicking and dragging on the curve) to start bringing the curve over from its steep initial rise. We then finally add the last long straight section using a 3rd point on the curve, which keeps the star blowout under control. I believe this last part of the curve called "the long straight ride home" is due to Ron Wodaski.
With those preliminaries taken care of, let's try and get a reasonable looking image using the image processing power of PhotoShop and Noel Carboni's PhotoShop actions http://actions.home.att.net/Astronomy_Tools.html alone. I recommend you save the image file you are working with after every step as you proceed with the processing so that you can easily backtrack, or take different routes at any stage to see what happens.
Open up the original Pleiades file in PhotoShop, and click on Image/ Adjustments/Curves. Drag the curve into the Magic Curve shape shown in Figure 10.5 and note as you do so that the nebulosity brightens up without losing control over the star brightness. Make sure you also have the all-channels histogram open, Window/Histogram/RGB so that you can keep an eye on the luminance channel as well as the individual RGB channels. Remember the Golden Rules at the beginning, we don't want clip the black or white ends of the histogram data, clipping loses you information, and you will see clipping if your dark data ends in a sheer vertical wall rather than a steeply falling curve.
Next we are going to carefully adjust the levels. Go to Image/Adjustments/Levels and note that you get a luminance histogram in this window too (it's that important!). Adjust the black level by moving the left hand pointer slightly to the right to where the data is about to rise steeply, keep a close eye on the histogram to make sure you do not "clip" any data. Do not touch the right hand (white point) pointer, but instead move the centre (gamma) pointer slightly to the left to brighten up the whole image a touch. When you are happy with your level (linear stretching) changes, click o.k. and save the file again.
The colour looks a little washed out. Go to Image/Adjustments/Hue/Saturation and increase the saturation by 20% and click o.k.
You will see some lens flare and a few hot pixels (maybe the odd green star too) in the image that you wish to "clone out". Click on the Clone Tool (the one that looks like a rubber stamp) with mode normal, opacity 100% and flow 100% and with a brush size to suit the object you wish to remove. At this point it is worth zooming in a couple of times [View/Zoom In] so you can see what you're doing. To grab a piece of the background that you want to place over the defect, hit the Alt button and simultaneously left-click - this will "pick up" what's behind the cursor. Now move the cursor over the defect you wish to remove and left click - the defect is now buried beneath the piece of background you picked up elsewhere. It clearly makes sense to pick up the background in a region as close as possible to the defect so that it all merges in nicely afterwards. Proceeding in this way, clone out all the defects that you find detract from the image - remember, this is not scientific work, this is creating a pretty picture, and you cannot use this image for "scientific" purposes.
We like to be able to concentrate on nebulosity and not have stars overpowering the image - time to use some of Noel Carboni's actions. Simply click on Make Stars Smaller, and then click on Make Stars Smaller again.
The curves process has brightened things up, but also shows us quite a bit of noise in the image. Click on Space Noise Reduction followed by Deep Space Noise Reduction. Next click on Enhance DSO and Reduce Stars.
I now want to darken things down a little in a controlled way, so first apply the "lazy S" curve as shown in Figure 10.6. Now go back into levels and move the gamma point slightly to the right making sure, once again, that you don't clip the black point at all.
Finally apply the "downward curving bow" curve as shown in Figure 10.7 to finish off processing this image. Your image should look something like that shown in Figure 10.8 which I hope you find reasonably satisfactory.
Remember, this is all very basic stuff and over time you will refine these basic steps to fulfil your own needs. We haven't removed light pollution, or colour gradients from this image, but using Noel's Tools these are simple one, or two-step operations anyway.
Please find here http://img141.imageshack.us/my.php?image=ngc1977both datasetssdmaut6.jpg some rather nice data for the Running Man nebula (NGC1977) in Orion taken with the Hyperstar and the SXV-H9C one-shot colour camera. Use a combination of PhotoShop and Noel's actions to see if you can turn Figure 10.9 into Figure 10.10. I took 28 steps to get this result - happy processing.
Was this article helpful?