De-Blooming tool

[Priami]

Hi,
I am a new Commercial user. I would like to know if there is some tools (available in the current version or under development) to solve blooming issues.

Thanks!

Regards,
Leonardo Priami

[vicent_peris]

Hi Leonardo,

You can solve the bloomings using shorter exposures and making a composition with the longer ones with the HDRComposition tool. I think Georg Viehoever a also wrote a tool to solve the same problem with gradient techniques, but in any case you're going to need the shorter exposures.


Regards,
Vicent.

[georg.viehoever]

Leonardo,
have a look at thread http://pixinsight.com/forum/index.php?topic=5023.msg34770#msg34770.

In general, deblooming in the traditional way "paints" data into the spikes where simply not data exists, and therefore is not considered good practice. You can avoid them without "painting" by observational techniques, such as HDR exposures or rotated cameras.

Georg

[mschuster]

Georg,

Just thinking about a deblooming integration with a rotated camera: Suppose sensor is square and frames are from two camera rotations, 0 and 90 degrees, all frames dithered.

Align all frames and create two integrations, one for each rotation. Compare integrations pixel-wise, marking bright pixels on one integration with dim counterparts on the other as "bloomed pixels".

Use these bloomed pixel maps as rejection maps in a new integration with all frames. In other words, integration does normal rejection as usual, but it also respects the bloomed maps as additional pixels to reject in the stacks.

The resulting SNR in the bloomed areas will be a factor of square root two less that elsewhere, assuming about equal number of frames in each orientation.

Run a noise reduction on the integration, using some sort of a merging of the bloomed pixel maps as a mask to slightly denoise only the bloomed areas.

Would this work?

Thanks,
Mike

[georg.viehoever]

Your method would probably work. But I think simple integration with with rejection should also work if you have at least 3 rotation angles. In this case, 2 rotations will always overrule the bloomed pixels in the third one. I am not sure if it is possible to tune rejection in ImageIntegration such that it does the same with only 2 rotation angles in the source set.
Georg

[mschuster]

I agree 3 rotations or more should work fine with the existing ImageIntegration, and likely only 2 is asking for trouble.

But more than 2 implies that larger areas have lower SNR, which would be nice to avoid.

Also another thought: maybe the existing II rejection map is useful as a denoise mask, that is, it identifies pixels that have lower SNR?

Thanks,
Mike

[georg.viehoever]

If you do n rotations in n shots, the different SNR will be barely noticable (and significant only close to the star, where brightness is high anyway). Large n is probably unrealistic, since you also need n master flats, but n around 5 should be within reach....

Why dont you use HDRCombination (with a couple of short shots to fill in the bloomed areas) instead of rotated cameras? That also takes care of burned out stars. It probably has a similar SNR issue as 3 rotations, but if you dont have a rotator....

Georg

[mschuster]

Worried that a couple of short shots will leave bloomed areas with poor SNR, especially when blooms cover dimmer nebulosity that require more time.
Mike

[pfile]

Also another thought: maybe the existing II rejection map is useful as a denoise mask, that is, it identifies pixels that have lower SNR?

!! great idea. i think you'd have to crank the rejection parameters way down to get something that looks more like your image (for me a good rejection map is only rejecting obvious hot pixels, cosmic rays, airplanes and the like). i guess then maybe smooth the rejection image and use as mask during TGV or similar.

rob

[Priami]

Thanks for reply to everyone.
One question: I have an Apogee Alta F9 (KAF6303), so this is NOT a square sensor. If I use rotation solution I will lose the 35% of area of the sensor. Or not?
Thanks
Leonardo

[georg.viehoever]

Yes, you would loose some effective sensor area. You can reduce the loss by doing rotations<90 degree.
Georg

[dgbarar]

HDR does work to eliminate the blooms but it does present another problem.  The HDR images are 64 bit and when attempting to display them in the linear state they can be heavily posterized.  If one wants to use TGVDenoise, decovolution, et.al (which need to be done while the image is linear) it can be very difficult to optimize the parameters as it is difficult to see what was done through the posterization.  To optimize, one must iteratively apply the tool, perform a non-linear stretch, evaluate the results and repeat over and over again.  This can be very time consuming.

All of us in the user community anxiously await a release of Pixisight that provides for more than 16 bit resolution for the STF to significantly reduce the posterization of 64 bit images and hence improve our processing.

Cheers,

Don Barar

[pfile]

hang in there

[vicent_peris]

It's coming, now working fine in my computer.

V.

[dgbarar]

Hi Vicent,

Thanks for letting us in on the secret.  Might I ask when you think it will be ready to release?

Cheers,

Don