NGC 253 - now with added Ha

pvelez (Pete) · #1 08-09-2012, 04:06 PM

I collected about 1 hour of Ha for NGC 253 last week. Just for fun, I thought I'd play with an existing LRGB image. Its my first serious attempt at adding Ha and I'm pretty happy with it.

For comparison, here is the original LRGB image posted a few weeks back as well.

Of course there is too much red - I'll need some more RGB data to tone it down.

Comments welcome

Pete

strongmanmike (Michael) · #2 08-09-2012, 05:00 PM

Not too much red at all, looks great Pete

Mike

pvelez (Pete) · #3 08-09-2012, 05:57 PM

Thanks Mike

The Ha does make it easier to get a better colour balance - and so much easier to collect in suburban Sydney

Pete

RobF (Rob) · #4 08-09-2012, 06:17 PM

Hi Pete

This is fascinating to see the final product. I hope you don't mind me linking, but I've been comparing to the red that came out on a pure LRGB image of mine - always wondered what added Ha might do.
https://picasaweb.google.com/UserRob...15896803809666

I don't think you've overdone the red either (and its easy to do, upsetting the purists in the process!)

tilbrook@rbe.ne (Justin Tilbrook) · #5 08-09-2012, 06:23 PM

Great silver coin Pete!

It's great to see where the red is supposed to be on this galaxy. Mikes right, the amount of red looks fine.

Cheers,

Justin.

alpal · #6 08-09-2012, 07:20 PM

That's great - the Ha is bringing out the red nebulas inside the galaxy.
Still - it's a tough target from the suburbs.

pvelez (Pete) · #7 09-09-2012, 10:41 AM

Quote:

Originally Posted by RobF

Hi Pete

This is fascinating to see the final product. I hope you don't mind me linking, but I've been comparing to the red that came out on a pure LRGB image of mine - always wondered what added Ha might do.
https://picasaweb.google.com/UserRob...15896803809666

I don't think you've overdone the red either (and its easy to do, upsetting the purists in the process!)

Rob

very happy to have a link to your image. Its always instructive for me to see what others are doing with their data. I'm finding processing is harder than imaging now.

I find with the Ha that the knots of star forming regions really stand out but if I'n a bit light on RGB, it can be overwhelming. I've been playing with NGC 300 which is a more challenging target. The Ha regions really impact on the overall colour of the galaxy.

Pete

pvelez (Pete) · #8 09-09-2012, 10:42 AM

Quote:

Originally Posted by tilbrook@rbe.ne

Great silver coin Pete!

It's great to see where the red is supposed to be on this galaxy. Mikes right, the amount of red looks fine.

Cheers,

Justin.

Thanks Justin

Pete

pvelez (Pete) · #9 09-09-2012, 10:43 AM

Quote:

Originally Posted by alpal

That's great - the Ha is bringing out the red nebulas inside the galaxy.
Still - it's a tough target from the suburbs.

Cheers. I'm only now appreciating how tough it can be get good data from the 'burbs.

Pete

naskies (Dave) · #10 09-09-2012, 12:58 PM

Very nice, Pete. I love those little red nebulae patches sprinkled throughout the galaxy.

RobF (Rob) · #11 09-09-2012, 04:18 PM

Quote:

Originally Posted by pvelez

Rob

very happy to have a link to your image. Its always instructive for me to see what others are doing with their data. I'm finding processing is harder than imaging now.

I find with the Ha that the knots of star forming regions really stand out but if I'n a bit light on RGB, it can be overwhelming. I've been playing with NGC 300 which is a more challenging target. The Ha regions really impact on the overall colour of the galaxy.

Pete

Thanks Pete - almost took it down later thinking I'd been rude.
Would be interested to hear what software and Ha blend technique you used. I've only even tried a Ha galaxy blend once, and it wasn't pretty

pvelez (Pete) · #12 10-09-2012, 07:52 AM

Quote:

Originally Posted by RobF

Would be interested to hear what software and Ha blend technique you used. I've only even tried a Ha galaxy blend once, and it wasn't pretty

Rob

I've been using Pixinsight. The Ha blending technique is detailed in the Harry's Astroshed video tutorials.

The process is a bit convoluted and I don't pretend to understand it fully. Initially, you combine your RGB images andfix up any gradients. You then extract the R, G and B channels. Using a funky Pixelmath formula, you use the R channel to tone down the Ha image. The aim is to reduce the Ha in the body of the galaxy and any closer stars in the frame - otherwise you end up with bloated stars. If you do this correctly, you can isolate those sections of the star forming regions in the galaxy that you want to highlight.

This adjusted Ha frame is then combined with R to create a new R frame. Another Pixelmath formula achieves this. This new R frame is then combined with the G and B frames and you travel on from there.

The beauty of the technique is both instances of Pixelmath can be altered depending on the weighting you want to achieve. In theory the bandpass of your R and Ha filters will dictate the weightings but I found that I needed to drop the Ha component significantly so it doesn't overwhelm the image. I suspect that its a function of the low level of signal in R - I combined 1 hour of Ha with 1 1/2 hours R.

Here's the link if you want to see how it works in practice:

http://www.harrysastroshed.com/Hagalaxy.html

Pete

RobF (Rob) · #13 12-09-2012, 10:47 PM

Thanks Pete.
Yes, the Ha combination in PI (and other software) can be very much a feeling thing more than science. Appreciate the link and description.

gregbradley · #14 13-09-2012, 09:29 AM

Ha version looks best. The red is a bit too dominant and takes over the image too much in my opinion. Pulling it back a bit would make the image more balanced.

Greg.

Ross G · #15 14-09-2012, 10:33 PM

Great looking galaxy photo Pete.

Ross.

Larryp (Laurie) · #16 14-09-2012, 10:52 PM

Very nice!