Las first images of the James Webb such as the Carina Nebula or the Wagon Wheel Galaxy They are fantastic photographs with which we are dazzled. They show scenarios full of contrasts, depth, color and brightness.
But, Did you know that they don’t come from the telescope like this? The device delivers these images through the antennas that are on Earth in raw format known in astrophotography as FITSsimilar to what would be the format in digital photography RAW (contains all of the image data and can be exploited and explored in editing). These are heavier than the recognized JPG or PNG.
The final astronomical photographs published by NASA and spread around the world are thus the result of a photographic calibration that scientists dedicated to this work do. Professor León Jaime Restrepo Quirós, professor at the Faculty of Engineering of the University Institution of Envigado (IUE), explained that the Telescopes capture images in the filters provided by their technology.
The James Webb does it in the filters of the visible and infrared spectra and thus the images are obtained in both spectra with their different filters. The teacher explains that one of the photographic systems of the visible spectrum is the UBV photometric system, also known as the Harold Johnson System for stellar classification governed by the color of the star, in which there are ultraviolet, blue and visible spectrum colors. These colors are chosen by astronomers depending on what they want to highlight, but these they are not faithful to those of the cosmic landscapes.
“The images of each filter are monochrome photographs, that is, in gray scale. Some of them arrive dark and with low brightness because they had a short exposure time, that is how the images that are captured of the stars are generally, which tend to arrive very flat. While if the image was subjected to a high exposure time, very bright images will arrive. That is where the calibration of each of them is done”, assured Restrepo Quirós.
The compressed version of FITS is the .FITSFZ format (slightly lighter than the raw, original format). It is in this format that the images receive their final treatment and then, when calibrated image, with striking colors for human eyes and with better contrast, delivered in easy-to-disseminate formats.
“In the FIT format, what is done is that some points that appear in the raw photographs can be related to electrical coordinates and the brightness level can be measured,” added the teacher.
How is the calibration in the astronomical image?
They are rendered and calibrated in rendering programs other than commercial photo editors such as Photoshop or Lightroom. These images are processed in programs such as IRAF or MIDAS, what is the tool European Southern Observatory (IT’S).
The photos go through a process of “cleaning” the image, so that noise is removed and they are left with a balanced exposure of brightness and contrast. Bright colors are also chosen. There is a procedure called Masking and Bad PixelsIn this, all the “dirty” parts of the photograph are removed, such as the red dots that are seen in some digital images, the teacher said.
During processing, the following calibrations are performed
According to official page of the Observatory of Las Cumbres photographs, like those of the James Webb, must undergo these processes to be as striking as they are.
1. Bad Pixel Masking
2. Bias subtraction
3. Dark Subtraction
4. Flat field correction
5. Source code extraction (using SEP , the Python and C library for source code extraction and photometry )
6. Astrometric calibration (using astrometry.net )
7. The final data products are multi-extension FITS files with four extensions:
SCI: The Pixel Data Matrix (Science).
BPM: The Bad Pixel Mask.
ERR: the matrix of cumulative pixel uncertainties.
CAT: The catalog of sources detected by SEP in a FITS binary table. The catalog lists pixel positions (X, Y), semi-major and semi-minor axes (A, B), position angles (THETA), fluxes, and errors (FLUX, FLUXERR) for each source.
This is a little of the processing that the images undergo to be colorized and striking for you and anyone else.
The universe without the editing would look darker or brighter, but with astronomers dedicated to this technique, it is possible to see these astronomical landscapes as they are taught today.
