Well, here is my first installment on how I am learning to digitally "enhance" images originally captured on film. In a word...S-L-O-W-L-Y. I'm afraid I will never be a "Generation-d"er. I've had PhotoShop installed on my Mac now for 3 years (I'm still running version 4 !) and feel I am just now getting the hang of it. It is a massive and, without concentrated effort to understand, confusing application to use. There are simpler ones, some designed especially for astroimagers, but none of these are yet available for my platform.
First of all I would like to share some of my thoughts on using this method to enhance astrophotos. I struggled greatly for years with the idea of doing so at all. To me it seemed that it was somehow not right to show things that "aren't there". NASA's public relations problems caused when it was revealed that Mars is not so "red" and Jupiter's clouds not as vibrantly hued as shown in NASA press releases; and the problems caused when Time Magazine digitally removed someone from behind someone else on one of their covers (who those "someones" where I don't even remember but perhaps you recall the brouhaha it caused in the mainstream press) only bolstered my resolve that this type of digital legerdemain was "from the devil!" Had I still continued in this naive conviction I don't know what I would have done recently about the flap caused when Rolling Stone Magazine was forced to quell rumors that they had digitally "de-enhanced" certain tender portions of our V.P.'s anatomy on one of their covers.
My conversion was not achieved in a "Damascus Road" experience or any single moment of clarity. The scales fell from my eyes slowly over at least a couple of years. My first moment of clarity came one night when I was shooting through a nebular filter and realized that what was going to show up on the film was not what was "really there". Gradually I came to understand that no picture I would shoot would ever show anything that was "really there". All images captured on film, especially celestial images, are "surreal" at best. They are all, at least, magnified (even when shot through a venerable 50mm, "sees-it-like-your-eyes-do" lens), sometimes filtered; always dependent on the chemical response of whatever film emulsion is being used and whatever conditions or chemicals with which that film is treated before exposure and as it is developed. Indeed the whole process of gathering photons in one place for minutes or hours at a time greatly skews the result of the final image away from anything resembling what is "really there". Our eyes will never see the universe the way other imaging chemistries or methods do even through the greatest telescopes. And to bring out or enhance what the eye will never see on its own--but which is "really there" nonetheless just waiting to be uncovered--is what the art of photography is all about. In fact what the art of astrophotography and astroimaging IS.
Armed with the fruits of this rationalization I embarked on the road to freedom. I began to use many more filters than just nebular and L.P. rejection ones. I began using black tape masks on my lenses, and swapping several color filters through the length of an exposure. I began purposely fogging lenses with the moisture from my breath to capture a diffuse effect and double exposing scenes through different filters. This all resulted in a great deal of wasted film. But also netted a few, really neat pictures! It was a short hop from this type of "pre-meddling" to the digital darkroom. To digitally enhance contrast or color after the exposure is made is easier than all that filter swapping and camera winding in the dark. It also saves a lot of time wasted crawling around groping in cow manure for dropped filters. An added bonus is that all that "wasted" film can sometimes be rescued to reveal respectable images thus redeeming many hours of my life that would have otherwise been for naught.
Thank you for indulging me and following along with this personal catharsis. Now, let's cut to the chase. What can be done with digital image enhancement? The first thing I learned about is the magic of simply enhancing the contrast. The first thing I do is scan the film into my Mac using a Minolta Dimage Negative/Slide scanner. I always scan at the largest pixel number available. With my scanner that is 3504 x 2336 pixels. This results in a whopping huge file of around 23 MB but when you're dealing with astroimages, the more info you have to work with, the better. I normally then save the scanned image as a TIFF file. Also resulting in a large file. But for the purposes of sending this correspondence to you via the internet I will be saving them as medium/small sized JPEGs so I can send it--and you can open and read it--in somewhat less than 5 or 6 hours.
I then open the image in PhotoShop (click on any of the images to get a larger version).
As you can see the raw image of M51 leaves a lot to the imagination. The next thing I do is crop the image to center the subject a little better
This action reduces the file size. It also removes any dark edges from the
original scan. Even though you can't see them because the sky background is
pretty dark, they're there. Those dark pixels around the edge of the picture
would "confuse" the program when I go to the next command under the Image
menu; Image>Adjust>Auto-Levels. This command averages color/contrast levels
across the entire image. Sometimes this command works wonders...sometimes
not. So I wait and see what I get. If I don't like it then I don't save the
changes (Edit>Undo) and will resign myself to going in and monkeying with the
color/contrasts as individual items.
In this case, the results were O.K. so I decided to apply the Auto-Levels and "massage" them a little. The next "tweak" was to go into the Brightness/Contrast command;
Image>Adjust>Brightness/Contrast, and adjust the Brightness setting to around
-25 or -30, and the Contrast setting to about +30.
To my eyes the color is still just a bit off so I enter Levels;
Image>Adjust>Levels and manually move the the left hand arrow to the right
until the input level under RGB (Red Green Blue) is around 10.
Finally I apply a little bit of a Gaussian Blur to soften the edges of the
stars; Filter>Blur>Gaussian Blur..., setting the Radius to around 2.0 pixels.
I would then save the final result as a TIFF file on a ZIP disk for possible later conversion to a 35mm slide at Sukulski-Brunelle or similar purveyor of digital imaging services. There are many permutations on the steps and procedures I used in processing the image of M51. Any can be explored and used to achieve satisfactory results. As I said PhotoShop offers almost unlimited possibilities as do, I'm certain, most other image processing software applications. In the end, the astroimager must decide what is appropriate. What was done above I consider to be a low level of manipulation that highlights the subject rather well and is still true to the "spirit" of the original film image. Thanks for reading. Please feel free to ask questions.