Emphasizing Red in M27

[LX200]

New to PixInsight... and to my QSI 683 imager... so I am used to DSLR work, working LRGB is new to me.

Anyway.. I am having trouble figuring out how to emphasize the red structures in the interior of M27.

My LRGB combine has nice detail in there, I can see it, but I just don't know how to bring out that red... it is very dull... a lot of G and B color mutes the red.

How can I emphasize red?  What should I do to combine

1. Combine R,G,B as linear images with LRGB
2. Use Histogram Stretch to make RGB look balanced, as well as L histogram stretched to look balanced
3. Combine them

Or...

1. Stretch R, G and B separately
2. Emphasize R... stretch it more
3. Combine stretched R,G,B to get RGB
4. Add stretched L

I am using Astrodon LRGB filters.... don't know, maybe it's known that Astrodon filters create brighter B and G

I need a hint here....

[Geoff]

You could try the ColorSaturation process.  See attachment.  Experiment with the range and width of the peak.  I used Hue Shift to bring the red part of the spectrum to the centre of the window. Make sure you have used ColorCalibration in the earlier stages. I wouldn't advise differential stretching of the colour masters. You won't get good colour this way.
Geoff

[RickS]

Geoff's suggestion is a good one.

Another option for emphasising existing red areas in the image is to create a mask with ColorMask (http://pixinsight.com/forum/index.php?topic=7751.0), apply the mask to your colour image and then use CurvesTransformation to adjust (e.g. boost R, reduce G, boost saturation, adjust a* and b* curves, etc.)

If you want to boost areas of strong R signal including ones that aren't actually red because of even stronger G and B signal you could make a mask by stretching and black clipping your R master.  You may want to apply some noise reduction or a little Convolution blur to clean up the mask as well.  Apply the mask to your colour image and then use CurvesTransformation to boost the red (or reduce green, or ...)

Cheers,
Rick.

[LX200]

Hum... I guess I am going to have to figure out how to make a mask of just the nebula.... I don't want to saturate the stars.... I guess I make a star mask, and then invert it??  Is that right?  Then everything would be selected EXCEPT the stars, since I inverted a star mask?

Gotta figure out how to invert mask....  I guess pixel math or something to do that?  Or is there an invert mask command ??

[pfile]

you can invert any mask that's been applied to an image - right click on the masked image, Mask > Invert Mask.

you probably want to make a luminance mask from the image, then subtract a star mask from it. that will expose the nebula but protect the stars. you can use pixel math: lum_mask - star_mask.

rob

[LX200]

I tried all sorts of setting on Star Mask, and it seems to only pick up the larger stars from M27.... unless I stretch the image, then I see more stars... so, is it typical to do a star mask, and then having to stretch the image to bring out the smaller stars, before applying it as a mask.

[Greg Schwimer]

I'm still figuring out how to consistently create good star masks, but I'll share what's been working for me.


1. Create a luminance copy of your image.
2. Remove the large scale objects with MultiscaleLinearTranformation. Open the tool, reset to defaults, and double click the residual (R) layer. Apply to a preview. I'll add layers and move down from R until I get most of the nebula, etc off.
3. With StarMask tool, start with the defaults. If you're not seeing enough small stars, increase the noise threshold. I've had to go pretty high to get the little ones included.
4. Increase the scale such that larger stars become more well represented
5. In cases where you can't get them all into a single mask you can combine the masks with PixelMath using the formula max(mask1, mask2, ....)

If necessary, clean up any remnant non-star objects with CloneStamp using a black reference image. To create the black reference, use pixelmath formula of 0 (yes, zero), set to create a new image, and drop the triangle on your working mask. This will create a new image with pure black (pixels = 0). Click on the mask to start the tool, then move over to the black reference to set it as the reference.

[Greg Schwimer]

Here is a more thorough tutorial of what I outlined above:

http://trappedphotons.com/blog/?p=731

This also covers a similar process:

http://pixinsight.com/examples/M81M82/index.html