HaRGB

[papaf]

Hi all,
I'm approaching the ending of my 30 days trial, and this is something that still escapes me. How's the best method of handling an HaRGB image composition in PI?
What I'm trying to do is replicate Starizona's method of blending Ha into the red channel before composing the final RGB image. I just can't find the way to blend the two image together.
Or maybe is there another way altogether to do this in PI?

Thanks!

[vicent_peris]

Hi,

just do it in PixelMath. Put the right formula: red+h_alpha*k, where k is a number that multiplies the h-alpha channel to blend it into the redd one with the desiredd proportion. "red" and "h_alpha" are the identifiers of your red channel and h-alpha images, respectively.

Activate the "Rescale" option.


V.

[Juan Conejero]

Vicent has described the correct way to achieve this when you want to work with the red and Ha separate (that is, grayscale) images.

You can also mix your Ha with the red channel of a RGB color image directly. This has the advantage that you immediately see the end result.

Assuming that your H-alpha image has the "Ha" identifier (double click on its vertical view selector to change, or select Image > Identifier), the whole procedure is as follows:

1. Open PixelMath.

2. If necessary, click the "Use a single RGB/K expression" option to disable it.

3. Enter the following expressions respectively for the red, green and blue channels:

(1 - k)*$T + k*Ha
$T
$T

Note that this will leave green and blue untouched.

4. Enter the following in the Symbols field:

k=0.75

0.75 is just an example here; replace it with your actual combination factor. The value of k must be in the [0,1] interval (zero means no Ha at all; 1 means no red at all and full Ha).

5. Disable the Rescale option. We don't need rescaling because we are mixing red and Ha to sum up to a maximum of one (see the expression for the red channel above).

6. Apply the PixelMath instance to your RGB image (for example, drag the blue triangle).

Let us know how this works for you.

[Harry page]

Hi Fabio

Welcome to PI

I hope you are staying   


Harry

[mmirot]

Juan,

It would be nice if we had a module for this.
I generally blend some Ha into the blue channel also to avoid the dreded salmon pink color.
It gets tricky with all those Pixel math expressions to remember.

Right now is still find it easier to do in PS 

Max

[Simon Hicks]

I agree with Max on this.

Background neutralisation is easy in PixelMath, but when the BackgroundNeutralization and ColourCalibration processes came out it was a godsend.

Maybe a slider and a live preview so you can tune the blending ratio....plus the ability to bleed some into the blue channel to account for the H-beta like Max does would be really cool.

[Jack Harvey]

A year or two ago I started doig it this way and it still gives good results for me.
1.  Process the Mean Ha frame with decon, wavelets or what ever you deem to get a good Ha image.  Then mask the image and use ACDNR to smooth the periphery of the Ha nebula, somewhat aggressively.  Adjust mid point with Histogram (see step 2).

2.  Extract the Luminance from a processed RGB of the image using the extract channels, with L checked and a and b unchecked on the CIE button.  You can throw this away as you will not use it.  I did look at the Lum to adjust the histogram for the above Ha to be close to that of the Lum frame.

3.  Now extract the R,G, and B frames form the RGB using the Extract Channels but this time the RGB button.

4.  In LRGB Combination tool put the Ha frame in the Lum slot and the RGBs in the correct slot.  Add a slight amount of saturation (lower the sat slider 15-20%) and start with about 50% of Luminance contribution using the slider in the upper right.  You can run several diffferent percentages of the "Lum" which is really Ha and see how much is best by comparing the output images.

5.  Make final adjustments with histogram, etc

[Jack Harvey]

If you prefer to combine your Ha with the Red channel (80% ?) and a bit with the Blue (15% ?) then you can do this easily wit the LRGB tool.  Put the Ha in the Lum slot and the red in the Red slot - uncheck the Green and Blue slots, adjust the sliders to get the percentages you wish (this may take some trial and error) and execute.  Now you have an HaR frame.  Now Leave the Ha in the Lum slot uncheck the Red and Green slots and check the blue slot with the Blue frame inserted.  Again adjust sliders to get percentages, execute and you have a HAB frame.  Now you can put the HaR in the Red slot the Green in the Green slot and the HaB in the Blue slot (with R,G & B all checked).  I assume you have no Lum so leave Lum unchecked.  Execute and you have a HaR-G-HaB image in 32 bit, not the 16 bit PS gives<G>.

[Carlos Milovic]

Suggestions for a propper name? ChannelMixer? NarrowColorBlend? Something that sounds generic

I agree with Jack that this can be done with LRGBCombination... maybe a bit tricky, but not that hard. Anyway, writing a new process that just merges one gray image with any color channel, in a given ratio, is quite easy to implement, so it won't take more than a day (finger crossed)

[Harry page]

Hi Carlos

The Narrow Band mixer has been mentioned before, and would be of a great help, and ideally would like to

1) Have a way of blending the narrow band into either L R G B at the same time

2) Real time preview would be fantastic and nearly a must ( sorry did I just swear )

3) Adjustable sliders for the amount

This relatively simple tool would put PI way in front 

regards Harry

[Jack Harvey]

Carlos  It may not take more than a day, but it will only be in Windows:-((<G>.

By Jove Harry, you have hit all the salient points!  Tutorial to follow?

[twade]

Carlos, et al,

Oh, I'm looking so forward to this module.  I have great difficultly adding Ha to my wide-field shots.  If you find you need a tough test image, you may use my wide-field M45 files under the twade directory.  They include L, R, G, B, and Ha.  The color data is a little weak.  This was taken before I found out how long I really need to expose the target through the color filters.

Wade

[papaf]

Well, what can I say? It worked wonders! It came out better than before!
If you want, look at the result:
http://discoremoto.cheapnet.it/papaf/Astro/ngc6888_HaR_RGB.jpg

Thanks to all! I have a decision to make... 

Fabio

[Niall Saunders]

Isn't what we need a 'generic' 3-channel mixer, with a fourth channel 'overlay'

The user decides what goes into each R, G, B and Lu channel. The GUI allows a mix or blend of those channels (isn't this effectively the LRGB Combine tool?). Each channel can be an image that is being 'blended' from other images, with its own GUI. And all 'live'.

In haste,

[Jack Harvey]

Fabio  Glad this worked for you.  The image is coming along well.  You might try taking a bit of green out by using the SCNR tool with the default settings, then open the colorsaturation tool and add 0.15 to 0.20 saturation with no hue shift.  I f you want to go further some wavelets will bring out more detail.  But I think you are on the right tract.