De-Blooming tool

[vicent_peris]

Well, it depends completely on Juan... I guess we'll have a new release in the next weeks. It will have 24-bit STF.


V.

[dgbarar]

24 bit STF!!!!!  That's even better than the 20 bit that Juan quoted a few threads back.  Yippee.

Don

[vicent_peris]

My Iris nebula (HDR from 1200s to 0.7s exposures) is still somewhat posterized at 24 bits ).

[dgbarar]

Hi Vicent

What are the limiting factors that prevent developing an STF resolution higher than 24 bit?

Cheers,

Don

[vicent_peris]

I think we don't need more bits than 24... The Iris is a very special case.

The limiting factor is the LUT table size and the time to calculate it. A 24-bit LUT table has a size of 16MB per color channel (this is independent from image size). A 28-bit LUT table would have a size of 256 MB per channel, so for each opened color image you would need an extra of 768 MB RAM space (even if the image is 1 mp size).

24 is a very good option IMO. It's a good compromise between visualization accuracy, LUT table size and calculation time.


Best regards,
Vicent.

[dgbarar]

Hi Vicent,

Thank you for the explanation.

I have studied your processing of the Iris Nebula (Dynamic Range and Local Contrast Tutorial), learned much, and have incorporated many of your concepts into my own image processing.

That said, what makes your Iris Nebula a special case that makes it more prone to posterization when applying the STF to the linear image.

Don Barar

[vicent_peris]

Imagine the bloomings of a 7th magnitude star with a 1.23 meter telescope and a CCD camera with a QE of 90%...

The shorter exposures were about 0.7 seconds while the long ones were 20 minutes.


V.

[dgbarar]

Hi V,

Would I be correct in saying that the amount of posterization is related to the ratio of long/short exposures for the HDR composition?  In your example the exposure ratio is approximately 1700.  I know each subject is going to be different depending on what one is attempting to accomplish.  Based on your experience what would you say is maximum HDR exposure ratio that one can use and have minimum posterization?  Or, am I being really naive and attempting to oversimplify?

Don Barar

[Juan Conejero]

Hi Don,

24-bit STFs are now working perfectly fine in the current development version of PixInsight 1.8.0. We are very close to the public release.

The specific case of NGC 7023 that Vicent has mentioned is a very extreme case. In this screenshot you can see how the image looks like with the traditional 16-bit STF (left) and the new 24-bit STF (right):

This image still shows a little bit of posterization in the darkest areas, even with 24-bit screen LUTs. To be completely free from posterization, this image would need a 28-bit STF, which is impractical for obvious reasons.

20-bit screen LUTs are sufficient for the vast majority of HDR linear images. In fact, we had implemented 20-bit STFs, which were working fine for all of our test HDR images, until Vicent uploaded this 7023 image for testing. This image "convinced" me of the necessity to reimplement STFs using 24-bit LUTs instead of 20-bit, but it is definitely a truly borderline case as I have said.

[dgbarar]

Hi Juan,

Thank you for posting Vicent's Iris Nebula.  It was good to see the impact of 16 vs 24 bit STF resolution.  It really does make a significant difference.  I have several 64 bit HDR images I holding up processing because I am having difficulty optimizing noise reduction parameters. We all are eagerly waiting the release.

Cheers,

Don Barar