{"id":37281,"date":"2022-10-20T00:00:00","date_gmt":"2022-10-20T00:00:00","guid":{"rendered":"https:\/\/c01.purpledshub.com\/bbcskyatnight\/?post_type=purple_issue&p=37281"},"modified":"2023-03-30T09:07:13","modified_gmt":"2023-03-30T09:07:13","slug":"processing-making-your-own-images-from-jwst-data","status":"publish","type":"post","link":"https:\/\/c01.purpledshub.com\/bbcskyatnight\/2022\/10\/20\/processing-making-your-own-images-from-jwst-data\/","title":{"rendered":"Processing: Making your own images from JWST data"},"content":{"rendered":"\n
PROCESSING<\/span><\/h5>\n\n

Making your own images from JWST data<\/span><\/h2>\n\n

Download and put your own spin on observations from the world\u2019s largest space telescope <\/p>\n\n

\"\"
The author\u2019s rendition of NGC 3132, the Southern Ring Nebula, processed from freely-available JWST data <\/figcaption><\/figure><\/div>\n\n

We live in rather amazing times, with private citizens travelling to space and citizen scientists contributing to the knowledge base of professional astronomy. Now, just as it did with Hubble, NASA has made data from the James Webb Space Telescope (JWST) available for download, for anyone to process for themselves. Here we walk you through, step by step, how to do it. <\/p>\n\n

Start by searching for \u2018MAST Portal\u2019 in your web browser or visit mast.stsci.edu\/portal\/Mashup\/Clients\/Mast\/Portal.html<\/a>, an archive named after Barbara Mikulski, a retired US senator and staunch supporter of space exploration. Clicking on \u2018Advanced search\u2019 at the top of the page opens a new window. On the far right, type \u2018JWST\u2019 in the \u2018Mission\u2019 box and press \u2018Enter\u2019. At far left, under \u2018Columns\u2019, select \u2018Release date\u2019 and scroll down to the box of the same name. Type \u20182022-07-13 14:00:00\u2019 as the beginning date and time \u2013 13 July 2022 being the day on which the first observations were released to the public.<\/span><\/p>\n\n

With the end date at default (the year 2050), note the number of \u2018Records found\u2019 at the top of the page. At the time of writing, there were already over 120,000 in the archive. As NGC 3132 is our target and was one of the first data sets released, entering an end date of \u20182022-07-13 16:00:00\u2019 displays a manageable 2,325 records. Clicking \u2018Search\u2019 at top left reveals the individual file folders and you\u2019ll need to narrow the field yet again. <\/p>\n\n

Under \u2018Instrument\u2019 in the \u2018Filters\u2019 box at left, choose the near-infrared data by checking \u2018NIRCAM\u2019. Depending on the width of your monitor and browser window, you may need to use the scroll bar at the bottom to slide over to the \u2018Target name\u2019 column. Also note the \u2018Filters\u2019 column. I found F187N, F356W and F444W to be the most useful filters. Click on the floppy disc icons of records 13, 15 and 18 to download the zipped folders to your computer (see Figure 1). <\/p>\n\n

\"\"
Figure 1: Once you\u2019ve homed in on the data you need, download the desired folders by clicking the little green icons <\/figcaption><\/figure><\/div>\n\n
Colour choices <\/strong><\/h5>\n\n

Unzip the folder to a suitable location on your computer then open the parent folder, then a second folder with the same name and, finally, the JWST directory. Next, open the \u2018Nircam\u2019 folder, discarding all but the FITS file ending in \u2018i2d.\u2019 Double-clicking that file will open seven individual files in your program of choice, mine being PixInsight. <\/p>\n\n

Of these, the seventh and last to open has a _SCI suffix and is the only file that you\u2019ll need. When finished, you will be left with three files to post-process, each ending in \u2018i2d.fits\u2019, with the filter names f444w_f470n, f356w and f187n. <\/p>\n\n

Those of us who process narrowband images will understand the concept of \u2018mapping\u2019 data that\u2019s invisible to the human eye to colours that we can perceive. The same is true here. Rather than the emission lines of the Hubble palette, we\u2019re now dealing with Webb\u2019s near-infrared information. <\/p>\n\n

\"\"
Figure 2: NIRCam filter names and the colours associated with them. Use this to help you choose the colours to assign to JWST\u2019s near-infrared data channels <\/figcaption><\/figure><\/div>\n\n

How best to assign these filters? For guidance, search online for \u2018NIRCam Filters \u2013 JWST User Documentation\u2019 or visit jwst-docs.stsci.edu\/jwst-near-infrared-camera\/nircam-instrumentation\/nircam-filters<\/a>. There you will find a full-colour graph illustrating the transmission lines of each filter from short to long wavelengths. <\/p>\n\n

While there\u2019s no single, correct way to proceed, it made sense to me to assign the shortest wavelength data (F187N) to the blue channel, as blue is on the shorter end of the visible spectrum. Conversely, I mapped the long wavelength F470N data to red and the medium F356W to green. I found this to be the most aesthetically pleasing colour blend for this particular object, and strikingly similar to the Hubble SHO palette (see Figure 2). <\/p>\n\n

After marrying the channels with PixInsight\u2019s \u2018Channel combination\u2019 process, the images were cropped of edge artefacts and stretched with \u2018Histogram transformation\u2019 (HT). Transferring a \u2018Boosted autostretch\u2019 from the STF (Screen transfer function) to HT with the RGB channels unlinked provided a great start to good colour. <\/p>\n\n

\"\"
Figure 3: SCNR in PixInsight was used to remove an overly green cast from the stars. The odd diffraction spikes are a result of JWST\u2019s segmented mirror <\/figcaption><\/figure><\/div>\n\n

PixInsight\u2019s SCNR (Subtractive chromatic noise reduction) was then applied to reduce an undesirable green cast in the stars (see Figure 3). From there, a range mask was applied, so that contrast, sharpness and colour saturation could be boosted in the nebula only. <\/p>\n\n

As the data was so clean, no noise reduction was needed for our final image, which you can see at the top of the page. If you\u2019re a Photoshop-based processor, be sure to view Nico Carver\u2019s excellent tutorial, \u2018Can I process the JWST data better than NASA?\u2019 on his \u2018Nebula Photos\u2019 YouTube channel (www.youtube.com\/watch?v=DVuonz26P0w<\/a>). <\/p>\n\n

<\/div>
\n
3 QUICK TIPS <\/h5>\n\n\n\n

1. <\/strong>Knowing the release date of a particular data set will help narrow your records search considerably. <\/p>\n\n\n\n

2. <\/strong>Note that the strength of the NIRCam\u2019s infrared signal may render noise reduction unnecessary. <\/p>\n\n\n\n

3. <\/strong>While gathering the data is a rather tedious process, the end result is well worth the effort! <\/p>\n<\/div><\/section>\n\n

\"\"<\/figure><\/div>\n\n

Warren Keller is an astrophotographer and image-processing educator. See www.mastersofpixinsight.com<\/a><\/p>\n\n

<\/p>\n\n

<\/div>\n\n

ALL PICTURES: WARREN KELLER\/NASA\/ESA\/CSA\/STSCI, NIRCAM FILTERS CHART COURTESY OF THE SPACE TELESCOPE SCIENCE INSTITUTE<\/p>\n","protected":false},"excerpt":{"rendered":"

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