APOD: The Cosmic Web of the Tarantula Nebula (2014 Feb 17)

[Chris Peterson]

Looking at the blue channel alone the stars are spread out much larger than the green and red and detail has been lost in the central nebula where it has become pure white.

Edit: This is not to say that this is somehow wrong. I think it's fairly typical and I've done it a lot myself.

I wouldn't choose the word "overexposed" for this. But certainly, the blue channel has had its intensity stretched more than the other two channels, with the result that the bright stars in the blue channel have been bloated. This results in blue halos around the stars in the full color image.

I like to work in LAB or HSL color spaces when processing astronomical images, because it largely prevents this kind of distortion.

[rgendler]

The colors in this image are somewhat muted, and the blue channel has not been given a boost.

Blue is actually quite overexposed in this image. To me, this picture is quite colorful--the opposite of muted. I'm not sure how you could say that it's muted.

Strictly from an image processing perspective the entire image is shift towards red. Even the blue stars are shifted towards purple which confirms my suspicion. This was done I'm sure to maximally enhance the tendrils of emission nebulosity abundant throughout the field. I would bet that dropping the mid-level of the red channel using curves would improve the overall color balance tremendously.

I agree, it's very red. I would suggest some changes to be made using Photoshop's channel mixer rather than the curves. We can take the purple out of the blues by changing the red output. Modifying its input to take +30% from the green channel and -30% from the blue channel is sufficient. This will avoid sacrificing brightness. To reduce the pinkness of the nebula we can then adjust the green output by modifying its input to +10% red channel and +90% green channel. The result should look like this.

I should note that I don't find any fault with Damian's original work, personally. Purple is my favorite color, anyway. I may have done it differently if I had done it but I enjoy Damian's version a lot. I recognize that even though the stars appear purple absolutely, relatively they are bluer than the nebula and that is sufficient for my brain to interpret the stars as being bluer.

I like your version. The color balance is now much improved. BTW I wasn't trying to be critical of Damian's fine image. Anyone who does serious astronomical image processing knows the benefit of another pair of fresh eyes.

[geckzilla]

I like your version. The color balance is now much improved. BTW I wasn't trying to be critical of Damian's fine image. Anyone who does serious astronomical image processing knows the benefit of another pair of fresh eyes.

Too true... many times have I come back to an image after not looking at it for a week or at least a couple of days so I can look at it with fresh eyes, myself. I have nightmares about my vision somehow being reduced and having to rely on the color picker tool to see for me...I guess that would reduce that bias that forms after staring at an image for hours on end. Nothing like grabbing the color picker and realizing what you thought was one color was actually not that color at all.

[geckzilla]

Looking at the blue channel alone the stars are spread out much larger than the green and red and detail has been lost in the central nebula where it has become pure white.

Edit: This is not to say that this is somehow wrong. I think it's fairly typical and I've done it a lot myself.

I wouldn't choose the word "overexposed" for this. But certainly, the blue channel has had its intensity stretched more than the other two channels, with the result that the bright stars in the blue channel have been bloated. This results in blue halos around the stars in the full color image.

I like to work in LAB or HSL color spaces when processing astronomical images, because it largely prevents this kind of distortion.

Lab confuses me. I use HSL (It is called HSB in PS) for my color sliders, though. That is a very sensible way to represent color. Munsell called it hue, chroma, and value. Apparently chroma and saturation aren't the same thing, though... I guess I have failed at making such a distinction for a long time.

[Chris Peterson]

Lab confuses me. I use HSL (It is called HSB in PS) for my color sliders, though. That is a very sensible way to represent color. Munsell called it hue, chroma, and value. Apparently chroma and saturation aren't the same thing, though... I guess I have failed at making such a distinction for a long time.

LAB can be confusing, but it's nearly ideal for working with astronomical images. It allows you to apply transfer functions (curves) without changing the size of stars across RGB channels, and to use filters like sharpening and blurring without creating colored halos. Try playing around with it. Convert to LAB to apply any filters and curves, then shift back to RGB to work more naturally with color balance (which should be subtle at that point).

[Ron-Astro Pharmacist]

Is the mechanism that causes star formation from a supernova known?

One might think that energy being released from a supernova explosion would drive the gravitationally attracted material apart rather than causing it to aggregate more vigorously.

[Chris Peterson]

Is the mechanism that causes star formation from a supernova known?

One might think that energy being released from a supernova explosion would drive the gravitationally attracted material apart rather than causing it to aggregate more vigorously. :?:

Most of the parent material is driven apart (but not all). But where fast material interacts with other material, you get shock fronts, where gas and dust pile up. Those concentrations are one of the things that can seed new star formation.

[RJN]

The colors in this image are somewhat muted, and the blue channel has not been given a boost. NGC 2070 is located nearly dead center of the image. Anyone looking for blue stars on the right of this picture will look in vain.

Thanks Ann! Fixed it. - RJN

[Elpatriarcasandokan]

In Spanish : Al acercarme se ven algunos discos con puntos en la mitad ?????
???????? ........ ?




?

[Beyond]

In Spanish : Al acercarme se ven algunos discos con puntos en la mitad ?????
???????? ........ ?




?

BING Translator= To bring me some discs are points in half
I say... ??????????????

[geckzilla]

They're wondering about the black dots in the centers of stars. If anyone can translate this to Spanish say it's just where the CCD is saturated. It got so bright that it turned black.

[Beyond]

They're wondering about the black dots in the centers of stars. If anyone can translate this to Spanish say it's just where the CCD is saturated. It got so bright that it turned black.

For what it's worth... here's the BING translation into Spanish = Si alguien puede traducir esto al español decir es sólo donde el CCD está saturado. Fue tan brillante que resultó ser negro.

And here is the translation of that translation, back into English = If someone can translate this to the Spanish say is only where the CCD is saturated. It was so bright that it turned out to be black.

So it looks like BING did a decent job of translating.

[geckzilla]

I wouldn't trust a machine translator to convey something like this that can be easily confused or I would have done it myself.

[Beyond]

Yeah, i was wondering about that. Guess we'll have to wait till someone who actually knows Spanish can say how good the machine translation is.