Hubble’s photo editor, Zoltan Levay, explains how he captures the invisible colors of the cosmos.
Zoltan Levay is eager to clear up a misconception about his job. Yes, he edits photos from the Hubble Space Telescope, but his work is not about subjective aesthetics. He’s an astronomer, and he’s not editing the images so much as enhancing them to reflect what’s really going on in distant galaxies. Thing is, galaxies can look awfully dim by the time their light makes it to Earth. Our eyes, which are wonderfully attuned to sunlight, are just plain “crappy,” Levay says, at seeing space, even in photographic form. So to make a vivid image of what’s actually going on in space, he has to make the invisible, visible. How? Here he describes his editing process for the “Pillars of Creation,” NASA’s iconic photograph of three gaseous plumes, 50 trillion kilometers in height, rising from a cluster of newborn stars in the Eagle Nebula, some 6,500 light years from Earth.
The raw materials
Hubble’s raw images arrive as black-and-white photographs. Each photo is taken three times at varying exposures, and then it’s Levay’s task to blend and combine to get the most accurate result. A distinct advantage of having three versions of the same image: Cosmic rays pepper Hubble’s light detector with random flecks of light and make the resulting images look like someone shook salt on them. By laying the three images on top of one another, Levay can spot — and remove — the rogue specks.
Once the images have been cleaned and stitched together, Levay adjusts the brightness of the pixels, each of which is assigned a value from 1 (pitch black) up to 65,000 (brightest white). That’s more shades of light than the human eye could ever detect, and often gradations in the images are so subtle, Levay can only spot the differences in the backend data of an image. He can accentuate the differences, however, by “clipping” the values of the brightest whites. Any pixel above a given threshold (say, 15,000), is set to maximum brightness, and the other pixels are brightened proportionately. The result? The tips of the pillars now shine nearly as brightly as the stars. “A few stars in this image are much, much brighter than anything in the nebula,” Levay says. So he suppressed their harsh glare, throwing the object of interest, the plumes of gas, into relief.
The Pillars of Creation may initially appear as pale, white plumes, but the elemental gases that make them — oxygen, hydrogen and sulfur — are actually tinged with faint colors. So you might discern a touch of cyan from the oxygen, a hint of red from the sulfur and a slightly lighter shade of red from the hydrogen. But when Hubble captures these lights, the resulting image is a pale muddle. How does Levay differentiate the colors? Photoshop. “We’re really translating colors,” he says, replacing the clouds’ subtler hues with vivid, primary colors. The images above, for instance, show his overlay of blue, green and red to accentuate the oxygen, hydrogen and sulfur in the plumes. And with that revised palette, he can repaint the pillars in colors that our eyes can more easily differentiate. Yes, it’s slightly artificial, but the colors help us see details of the pillars that might otherwise get lost. “By looking at these different individual elements you can tease out the structure,” Levay says.
Unleash the inner art critic
Levay then uses Photoshop to layer the red, green and blue images together. The result is a technicolor rendition of the nebula. But Levay isn’t done yet. “This just looks flat and muddy,” he says, “and it has an overall green cast to it, while the stars have a very strong magenta cast to them. That’s actually an artifact of the way the Hubble filters are designed.” At this point, Levay allows himself a little creative freedom, toning down the green, accentuating shadows at the center of the pillars and adding a hint of brightness to the tips of the plumes. The adjustments are slight and sparing. “You want to adjust it so that you keep those, as a photographer would say, shadow details,” he says.
Ready for mass consumption
NASA released this final image to the public in January 2015. Levay hopes it will give the public a better sense of the strange, invisible forces of the cosmos. Even after two decades of overseeing Hubble’s eight-person imaging team, he still gets a thrill from the finished product. “There are winds blowing from stars at hundreds of miles a second,” he says. “There is an immense amount of very high energy radiation going on in these clouds and that’s what’s causing them to have these forms. I hope the image gives people some inkling of the size, complexity and the dynamism that’s happening in a region of space like this.”