4 ms·

Related question: to confirm, some of the additional detail we’re seeing in the JWST images is in fact IR that has been “hue clamped” into the visible spectrum?

soulofmischief 4y ago
It's all IR. It's color-mapped over RGB, but the sensors are IR.
- wlesieutre 4y ago
  NIRCam’s range starts at 0.6 microns (600 nm) so picks up a little bit of the red end of our visible range. But it definitely can’t differentiate a range of human visible colors.
- rkagerer 4y ago
  Didn't the observed light shift into IR wavelengths due to the expansion of space over the last billions of years while it traveled to us? Do the recolored images have any relation to what the original view would have looked like, or is it just arbitrary "artistic license"?
  - deleted 4y ago
    [deleted]
  - jhugo 4y ago
    Looked like from what perspective? A human eye on Earth?
    - arjvik 4y ago
      OP clearly means from an observer moving at (approximately) the same velocity as the object emitting the light.
      - 9991 4y ago
        The objects aren’t really moving in that sense. The expansion of space over time is what stretches the light.
        jhoechtl 4y ago
        Without a fixed point of reference, what is the difference?
        9991 4y ago
        The difference is the expansion of space is accelerating over time. And certain wavelengths of light will be blocked by gas in the intervening space, and which light is blocked changes over time based on how red-shifted it is. Special Relativity isn't enough to explain this.
  - supernova87a 4y ago
    Hey, that's an interesting and uncommon question that I had not seen elsewhere -- They did not release or talk in much technical detail of how the images were assembled, which I'm sure will be done at some point. I do not think the colors do correspond (at least not deliberately), for 2 reasons: First is that the image of the Deep Field ("SMACS") contains galaxies at a range of redshifts. For example there may be galaxies quite near us (redshift z = 0 or close to 0) while others are more distant (the arced galaxies in the image being lensed that this image is famous for, at redshift z = 0.39), where redshift is the measure (1+z) of how much the wavelength light has been multiplied. So regardless of what color mapping you chose, it would not be a perfect fit for all objects in the field of view. For the galaxies near us in the image (z=0), the wavelengths being converted to RGB don't correspond to what we would see in the optical. Secondly, if it were remapped especially for the galaxy cluster of interest in this image, I don't think the colors are specifically tuned for that either. In more detail: Consider the optical color spectrum we see, ROYGBIV, or let me reverse it in order of increasing wavelength VIBGYOR -- and take the "RGB" 3 colors that might make up an image, or BGR to use that ordering -- this spans a wavelength range of say 400nm, 600nm, 800nm. The imaging filters available on the NIRCam span 900nm to 4400nm (4.4 micron) and there are 29 of them [0]. Researchers choose which filters to use based on what they wish to study. And recall that the imaging sensor actually outputs grayscale only, it is the filters that give it a color view and individual images in each filter are assembled to create a color composite. According to an example science program designed to take such images[1], the filters selected to be imaged might be 900nm, 1150nm, 1500nm. If you applied the redshift of the galaxies (divide by 1.39 from the above info about the cluster of galaxies), the above sampled wavelengths in the image would still correspond to redder parts of the spectrum compared to what is visible if we were seeing the galaxies now: 647, 827, 1079nm. So, no I don't think the color mapping was chosen to be accurate in a scientific sense of seeing what you would see if the galaxies were brought to the "original" view. [0] https://jwst-docs.stsci.edu/jwst-near-infrared-camera/nircam-instrumentation/nircam-filters https://jwst-docs.stsci.edu/jwst-near-infrared-camera/nircam... [1] https://jwst-docs.stsci.edu/jwst-near-infrared-camera/nircam-example-science-programs/nircam-deep-field-imaging-with-miri-imaging-parallels https://jwst-docs.stsci.edu/jwst-near-infrared-camera/nircam... ("select filters")
    - 4y ago
drbw 4y ago
Astrophysicist YouTuber Dr Becky covered this last month: https://www.youtube.com/watch?v=sNJR3lenz1I https://www.youtube.com/watch?v=sNJR3lenz1I

soulofmischief 4y ago

It's all IR. It's color-mapped over RGB, but the sensors are IR.

wlesieutre 4y ago
NIRCam’s range starts at 0.6 microns (600 nm) so picks up a little bit of the red end of our visible range. But it definitely can’t differentiate a range of human visible colors.
rkagerer 4y ago
Didn't the observed light shift into IR wavelengths due to the expansion of space over the last billions of years while it traveled to us? Do the recolored images have any relation to what the original view would have looked like, or is it just arbitrary "artistic license"?
- deleted 4y ago
  [deleted]
- jhugo 4y ago
  Looked like from what perspective? A human eye on Earth?
  - arjvik 4y ago
    OP clearly means from an observer moving at (approximately) the same velocity as the object emitting the light.
    - 9991 4y ago
      The objects aren’t really moving in that sense. The expansion of space over time is what stretches the light.
      - jhoechtl 4y ago
        Without a fixed point of reference, what is the difference?
        9991 4y ago
        The difference is the expansion of space is accelerating over time. And certain wavelengths of light will be blocked by gas in the intervening space, and which light is blocked changes over time based on how red-shifted it is. Special Relativity isn't enough to explain this.
- supernova87a 4y ago
  Hey, that's an interesting and uncommon question that I had not seen elsewhere -- They did not release or talk in much technical detail of how the images were assembled, which I'm sure will be done at some point. I do not think the colors do correspond (at least not deliberately), for 2 reasons: First is that the image of the Deep Field ("SMACS") contains galaxies at a range of redshifts. For example there may be galaxies quite near us (redshift z = 0 or close to 0) while others are more distant (the arced galaxies in the image being lensed that this image is famous for, at redshift z = 0.39), where redshift is the measure (1+z) of how much the wavelength light has been multiplied. So regardless of what color mapping you chose, it would not be a perfect fit for all objects in the field of view. For the galaxies near us in the image (z=0), the wavelengths being converted to RGB don't correspond to what we would see in the optical. Secondly, if it were remapped especially for the galaxy cluster of interest in this image, I don't think the colors are specifically tuned for that either. In more detail: Consider the optical color spectrum we see, ROYGBIV, or let me reverse it in order of increasing wavelength VIBGYOR -- and take the "RGB" 3 colors that might make up an image, or BGR to use that ordering -- this spans a wavelength range of say 400nm, 600nm, 800nm. The imaging filters available on the NIRCam span 900nm to 4400nm (4.4 micron) and there are 29 of them [0]. Researchers choose which filters to use based on what they wish to study. And recall that the imaging sensor actually outputs grayscale only, it is the filters that give it a color view and individual images in each filter are assembled to create a color composite. According to an example science program designed to take such images[1], the filters selected to be imaged might be 900nm, 1150nm, 1500nm. If you applied the redshift of the galaxies (divide by 1.39 from the above info about the cluster of galaxies), the above sampled wavelengths in the image would still correspond to redder parts of the spectrum compared to what is visible if we were seeing the galaxies now: 647, 827, 1079nm. So, no I don't think the color mapping was chosen to be accurate in a scientific sense of seeing what you would see if the galaxies were brought to the "original" view. [0] https://jwst-docs.stsci.edu/jwst-near-infrared-camera/nircam-instrumentation/nircam-filters https://jwst-docs.stsci.edu/jwst-near-infrared-camera/nircam... [1] https://jwst-docs.stsci.edu/jwst-near-infrared-camera/nircam-example-science-programs/nircam-deep-field-imaging-with-miri-imaging-parallels https://jwst-docs.stsci.edu/jwst-near-infrared-camera/nircam... ("select filters")
  - 4y ago

drbw 4y ago

Astrophysicist YouTuber Dr Becky covered this last month: https://www.youtube.com/watch?v=sNJR3lenz1I https://www.youtube.com/watch?v=sNJR3lenz1I