Learning Skyris: Drawing Color Out of Black and White
January 11, 2015
During his last flight, Commander William McCool described the view of the Earth below him, “The colors are stunning. In a single view, I see, looking out at the edge of the earth: red at the horizon line, blending to orange and yellow, followed by a thin white line, then light blue, gradually turning to dark blue and various gradually darker shades of gray, then black and a million stars above. It's breathtaking.” Monochrome cameras create stunning views of the universe in black and white, but the addition of three filters can release the hues of nature.
As Jupiter begins to climb into the night sky, it is the perfect time to begin imaging in color. With a monochrome Skyris camera, an LRGB filter set, and a Skyris filter wheel, beautiful color photographs capture details that single monochrome shots miss. Whole landscapes made by color elude the camera without LRGB photography; the Great Red Spot is no longer red and the ice caps of Mars don’t contrast with its orange desserts.
To begin your initial step into the realm of color photography, let’s look over some basic terminology used in the field. Advanced astrophotographers use LRGB, or “luminance, red, green, and blue,” photography to create stunning color images. By recording through each filter, specific details are emphasized. While this takes four times the processing of a singular monochrome shot, the LRGB method captures extreme detail and color.
A filter wheel can be attached to the camera, making the process magnitudes easier. This allows astronomers to simply flick the wheel and image through another spectrum of light. Parfocal filters also provide identical focuses for each filter, halting the need to refocus.
Jupiter is a fantastic planet to begin LRGB photography—large enough to show extensive detail, while also fostering strong, easily seen color contrast. As a first step, I strongly recommend downloading WinJupos, a freeware designed to stack LRGB Jupiter images into one color photo and show the user how Jupiter’s surface will appear at any given time. Once WinJupos is setup, you can plan your first attempt at a colorful Jupiter capture.
On WinJupos, under the “tools” menu, select “Ephemerides.” After customizing your own settings: latitude, longitude, year, and month, you can see how Jupiter will appear at any time or day. The most interesting photos of the planet display the four Jovian moons, their shadows, or the famous Great Red Spot (GRS).
You should also consider weather conditions before imaging; astronomical forecasts are excellent resources for determining sky qualities. Planning ahead when imaging will provide time to find a clear, crisp night; put together your filters, filter wheel, and camera; and cool your telescope to the outside temperature.
Once you are outside with Jupiter centered and focused in the live view box, it is time to image!
Histogram, a useful tool in iCap, is available under “View.” The tool allows you to track surface luminosity and, therefore, keep steady brightness between your four LRGB videos. For example, the blue channel (another name for the light passed through a blue filter) is darker than the green and red channels of Jupiter. Histogram will help you maintain prime brightness throughout your videos.
Another tip concerning settings in iCap is to set the gain as low as possible. A careful balance must be maintained, though. If gain is made too low and your image is darker, cursed onion rings are likely to form on processed images. One indicator of a perfect balance is your histogram; if it is at about 50% or more, no rings should appear.
Jupiter moves quite fast, as discussed in past blogs. To achieve a clear color photograph, you need to image and change your filters fast—this is why filter wheels come in handy. Each video capture: L, R, G, and B, shouldn’t be longer than a minute and transition time about ten seconds.
Once each channel is recorded, the final step begins: processing. As discussed in my last blog, AutoStakkert!2 accomplishes the best stacking of large files. It may be necessary, though, to first re-save the videos in Virtual Dub. After being stacked, load each image into Registax for final editing.
There are two different programs I have used to compress four monochrome images into a multi-colored image: Photoshop and WinJupos. Below are step-by-step instructions for each system.
WinJupos LRGB Combining:
- On WinJupos you first need to create image measurements using the “Image measurement” tool under “Recording.” To align your image with the Jupiter outline, use the arrow, “p,” and “n” keys. Save a measurement for each channel.
- Under “Tools,” select “De-rotation of R/G/B frames,” and plug in each measurement file. Not only will this combine the images, but it will also de-rotate them, providing even clearer photographs. If a blue ring appears on Jupiter’s surface, lower the LD value then compile the image again.
Photoshop RGB Combining:
- Open your RGB images with Photoshop in their own separate tabs; don’t copy and paste them on top of each other.
- With each tab select “Image,” “Mode,” and “Grayscale.”
- After all images have been converted to gray scales, select “channels” on the far right of the screen.
- Click the list icon, and select “Merge Channels.” A small box will appear with several options; choose RGB. Assign each image with R, G, or B, and a beautiful color Jupiter will be forged.
Photoshop luminance addition:
- Open the luminance image on another tab. Press “Select” then “All.” This will place an outline around your luminance photo.
- Copy this image: “Edit,” “Copy,” and paste it on the RGB photograph: “Edit,” “Paste;” the luminance layer should fully cover the previous photo.
- On the panel on the right side, select “Normal,” and scroll down to the last option, “Luminance.” This will merge the RGB image with the luminance layer, brightening the planet’s surface. To lower the effect, slide the opacity bar on the extreme right.
Note: Adding a luminance layer to the RGB image is only beneficial if it contains more detail than any other capture.
One final, crucial step after either Photoshop or WinJupos purifies the color balance of the image.
Registax color alignment:
- Open your LRGB image in Registax; the program will immediately prompt you to the Wavelets section.
- In the “Functions” tool group on the top right of Registax, click “RGB Align.” A small, green box will appear on the center of your image. Enlarge this box to envelop the entire planet: not the outlining moons, though. Press estimate on the popup box, and Registax will determine the color histogram of your image.
- Next select “RGB Balance” in functions, and a colorful chart will appear. Click “Auto Balance” to finish the entire processing stage.
While all of this work seems challenging and lengthy, the product is well worth the effort; highly detailed storms, colorful bands, and contrasting moons saturate LRGB Jupiter images. Single color images lack 66 percent of each channel when compared with LRGB photographs. Color channels also provide significant scientific data such as the chemical makeup of the planet’s surface. With a basic understanding of LRGB photography, the hues of nature are in your grasp.
Clear Skies, Happy Holidays,
Getting started with LRGB filter sets and filter wheels:
Parfocal LRGB Filter Sets: