Applying Luminance destroys my RGB images

[mstriebeck]

Hi,

I have two images that I took where applying the Luminance image (using LRGBCombination) destroys the RGB image (it darkens the RGB image A LOT and when I stretch it all details and colors are completely destroyed). Both, Luminance and RGB image are stretched and processed.

If somebody wants to help me figuring out what's going on:
Luminance: https://drive.google.com/open?id=1b02DanLyLIHUBkFzEu-1sR8nfuFlLMlH
RGB: https://drive.google.com/open?id=1vSmuL5xVOV749z41miC93iSGGPTfBEx_

I played with the Lightness setting in the LRGBCombination process as I thought that this might fix it - but to no avail.

Any ideas???

    Mark

[msmythers]

Mark

The images on the Google Drive were already stretched. All I did was apply the Luminance image to the RGB with the LRGBCombo tool. Here is my result. I cloned the RGB image to see the difference. No stretching, nothing other then the tool at default settings.


Mike

[mstriebeck]

That was weird that it just worked for you. I tried it again, and it didn't work.

... but after I restarted Pixinsight, I got the same results as you!

I have been using Pixinsight A LOT in the last 2 weeks (returned from a 5 night trip where I took a lot of images). Maybe some internal memory was corrupted or such...

Thanks!

[stevek]

I sometimes (often actually) find that combining the luminance to a colourful RGB bleaches out the RGB colors and makes them much whiter.
What's going on when that happens???

[msmythers]

Mark

Glad things worked out. Not that many years ago I would have been leaving my computers on, leaving programs running and never rebooting. With SSD drives as fast as they are now I no longer leave anything running these days. I don't have to worry about the old mechanical failures that hard drives created.

Mike

[niteman1946]

Hi Mark,

I’ve seen this same behavior a few times.  When it happens, a reboot clears up the problem.

Mark

[msmythers]

Steve

What generally causes the bleached out look is from the luminance image having a much larger median level then the RGB image. You want to start off with the 2 images being similar in level. Use the Statistics tool to be sure. The images don't have to be exactly the same just close for the best results. Here is an example where I just doubled the value of the median and the result is that washed out look. Once that happens it's hard to get things corrected.


Mike

[stevek]

Hi Mike, so how do you get the Luminance into the ballpark of the RGB image?  With Linear fit?
Steve

[msmythers]

Steve

You can't directly use linear fit with an RGB image and a grayscale image. You'll get a geometry error because of the different number of image channels. I don't shoot mono filter images so I'm not the best one to tell you how to prepare your images for the LRGB Combo tool for use with a luminance image other then the 2 images need to be similar in levels to avoid the washout effect. You can see the same effect using Curves and applying an aggressive Luminance curve.


Mike

[RickS]

how do you get the Luminance into the ballpark of the RGB image?  With Linear fit?

I find that roughly matching the stretch on the Lum and RGB is usually sufficient.  You can also adjust the balance between lightness and colour using the LRGBCombination Lightness and Saturation sliders.  Another option is to extract the Lightness from the RGB image then use it as a reference and apply LinearFit to the Lum.

Cheers,
Rick.

[chris.bailey]

If you head over to The Astro Imaging Channel, Adam Block has done a nice session on combining L with RGB.

[stevek]

Thanks Chris, I will check that out.

EDIT:  Wahren goes through this in Pixinsight Foundations Series 2, part 9.  He extracts the luminance from the RGB then uses that as the target for Linear fit from the master Luminance before combining the just extracted Luminance back into the RGB to ensure the RGB and Luminance are equalised.  THEN he uses LRGB combination to combine the Master Luminance and the RGB.  I have been struggling with this for ages and the penny has dropped!

[ngc1535]

Since my name was invoked...

It so happens I made the section on LRGB (a long section/demo) available for free/public. This is because during the AstroChannel live spot, I really messed up my presentation. Such is the case sometimes with live demonstrations. So you are welcome to visit this page:

https://www.adamblockstudios.com/articles/Fundamentals_LRGB

The YouTube session I did for the AstroImagingChannel is here:

https://www.adamblockstudios.com/articles/Astro_Imaging_Channel

You will find additional information on the page concerning some of what I presented.

If it is appropriate- perhaps someone would repost this to the tutorial thread if it deemed appropriate.
Thanks,
Adam Block

[stevek]

I was very impressed with Adam's session on The Astro Imaging channel and his method, I actually watched it with a whiskey a few weeks ago .  I have also watched the two free sessions on Adam's website and they show some very useful DBE techniques and a RGB spot removal technique that is completely new to me. So I think I am going to pay for his PixInsight Foundations series. 

When you consider the vast sums we have invested in our HW, a few bucks extra to acquire knowledge and techniques to process the acquired data sets seems pretty sensible really.  Otherwise one has a pile of unfulfilled data (like I have)!  Tons of high quality subs and I find I am just banging it together without much understanding.  I need more structure and understanding, personally speaking, about how to construct this data into higher quality pictures.

I also like Wahrens's videos too on IP4AP.
Steve

[Ron Kramer]

I experience this as well.  I use LRGB combine and I combine  NB this way.  I also wanted to include some LUM. When I do (even one) it seems to over power my other filters and they're really dark? I figured I can't do that. But now I read someone else is getting same with LUM and RGB.